when to use unsigned int

What if the numbers and words I wrote on my check don't match? Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. Most people seem never to question what they read: That's also presumably why everyone uses postfix. rev2023.6.2.43474. If overflow occurs, then the sign of the result is not the same as the sign of the mathematical sum of the two operand values."[1]. One of the reasons why I (personally) try to avoid unsigned types. As of Kotlin 1.3, Kotlin supports unsigned integers to accommodate this requirement. How to say They came, they saw, they conquered in Latin? And, have you considered compiling with "treat warnings as errors" to take it that one step further? It takes a size of 32 bits. Unsigned Integers Consider the following advocate example for using unsigned, unlike most posts here: In the above example, what happens if a negative value is passed in as thing_ID? C++ Core Guidelines and Google Style Guide advise against that, but do not elaborate enough why. But this cannot serve as a counter argument against using unsigned types, the task here is to simply get your loop right. Find centralized, trusted content and collaborate around the technologies you use most. A signed int can store negative values. This would allow you to have unsigned integer operations overflow silently, but signed integer overflows could trigger an exception which causes a context switch into the kernel without violating the C standard. Can I infer that Schrdinger's cat is dead without opening the box, if I wait a thousand years? It's quite a decade that i >= 0 is reported as warning by compiler if an unsigned int is used as type for i. In C programming language, unsigned data type is one of the type modifiers which are used for altering the data storage of a data type. Mixing signed and unsigned types can get you into a world of pain. val: the value you assign to that variable. Except for performance reasons (no answer actually deals with performance so far) it's just personal taste. What maths knowledge is required for a lab-based (molecular and cell biology) PhD? To guard against this you can simply add a static_assert to your program as follows: and it won't compile on architectures where int is 2 bytes. Unsigned types often have enough 'weirdness' that they should only be used in cases where their semantics are necessary. If E1 has an unsigned type or if E1 has a signed type and a nonnegative value, the value of the result is the integral part of the quotient of E1 / 2^E2 . In your example above, when 'i' will always be positive and a higher range would be beneficial, unsigned would be useful. Unsigned Variable Type of Integer Unsigned Integers Unsigned integers are used when we know that the value that we are storing will always be non-negative (zero or positive). When calculations involve both signed and unsigned types as well as different sizes, the rules for type promotion can be complex and lead to unexpected behaviour. Thanks for contributing an answer to Stack Overflow! 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. You should care about this when you're dealing with an integer that might actually approach or exceed the limits of a signed int. The first one declares a variable of type int with the identifier a.The second one declares a variable of type float with the identifier mynumber.Once declared, the variables a and mynumber can be used within the rest of their scope in the program. I agree with the educational issue. Maybe it's a better practice to not mix valid values with error indication in the same variable and to use separate variables for this. 1. By following the decimal constant rules in C99 section 6.4.4.1 Integer constants, we observe that the integer constant '1' has type 'int' or more explicitly 'signed int'. Did an AI-enabled drone attack the human operator in a simulation environment? In July 2022, did China have more nuclear weapons than Domino's Pizza locations? If length is also int, then you should use the same integer type, otherwise weird things happen when you mix signed and unsigned types in a comparison statement. Google) discourage use of unsigned integer types, and as far as I know neither Java nor Scala have unsigned integer types. Why is Bb8 better than Bc7 in this position? Finally, a nice trap: In a loop "for (i = 0; i < n; ++i) a [i] " if i is unsigned 32 bit, and memory exceeds 32 bit addresses, the compiler cannot optimise the access to a [i] by incrementing a pointer, because at i = 2^32 - 1 i wraps around. The PDP-1 was a one's complement machine that was still in production as late as 1969, and these machines were used well into the 1970's, so the idea of supporting one's complement was very much on people's radar back then. Thanks for contributing an answer to Stack Overflow! Mixed signed-unsigned arithmetic issues are detected by the compiler; just keep your build warning-free (with a high enough warning level). Their reasoning states that unsigned integers are 'intended as a form of self-documentation' for documenting that the value cannot be negative. When to use unsigned values over signed ones? The problem here is that you wrote the loop in an unclever manner leading to the erroneous behavior. About the use of signed integers in C family of languages. Since the positive maximum of a 32 bit integer is 2,147,483,647 then you should use an unsigned int if you know it will a) never be negative and b) might reach 2,147,483,648. In the first case, you'll find that the negative value is not greater than or equal to NUM_THINGS, and so the function will continue executing. Since this article was so popular, I've created a part 2. Enabling a user to revert a hacked change in their email. January 29, 2016 ios8, iOS9, Swift, Swift Programming, Tutorial How and Why To Use Unsigned Integers (UInt) In the beginning there was the unsigned integer, and it was good. This avoids any unexpected behavior doing arithmetic with signed and unsigned types, assuming the result of the expression fits into a signed int of course. That's perfect for programming a guided missile, but overkill (pun intended) if you're validating a web form. The C language provides the four basic arithmetic type specifiers char, int, float and double, and the modifiers signed, unsigned, short, and long.The following table lists the permissible combinations in specifying a large set of storage size-specific declarations. As outlined below, my reasons for saying that unsigned integers are better than signed integers are mainly related to the well defined behaviour of unsigned integers, and the relatively undefined (or implementation defined) behaviour of signed integers in overflow conditions and in certain shift operations. When I program, I like to be explicit, rather than use the safe option which could possibly have unintended consequences later (such as an overflow). 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. Another reason for me are annoying warnings, which make you write something like this every time: These are minor things, but they add up. Unsigned integers are there for a reason. The implementation may define typedef names intN_t, int_fastN_t, int_leastN_t, uintN_t, uint_fastN_t, and uint_leastN_t when N is not 8, 16, 32 or 64. Secondly, just because a certain guideline works for company X doesn't mean it will be the right fit for you. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Only when you're dealing with the size of something in bytes. 'Cause it wouldn't have made any difference, If you loved me. Many here mention "hard to spot bugs" but few give examples. This is stated quite clearly as 'Don't use an unsigned type' in the section 'On Unsigned Integers'. When is it appropriate to use an unsigned variable over a signed one? Just don't do something like "for (uint i = 10; i >= 0; --i)". If you do need to use signed integers you can find some overflow check helper functions. If you write any TCP processing code, you will definitely want to use unsigned integers. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. When I compile the following piece of code with VS2015 or GCC I see no warnings with default warning settings (even with -Wall for GCC). If you found this interesting, you might want to also check out my C compiler. If E1 has an unsigned type, the value of the result is E1 x 2^E2 , reduced modulo one more than the maximum value representable in the result type. Another possible benefit to allowing one integer type to have defined behaviour on overflow and one to have undefined behaviour, is that it would allow a conforming implementation to use a trap instruction (software triggered interrupt) for the undefined case. When you do arithmetic with your unsigned short variables and literals (which are of type int) or variables of type int, this ensures the unsigned variable will always be promoted to an int before evaluating the expression, since int always has a higher rank than short. In Germany, does an academic position after PhD have an age limit? char and 'signed char', are not necessarily the same. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Using int because it will cover up a programming error is scary. Since engineering standards themselves are created to be consumed by disciplined engineering activities (like ballistic missile warning systems), it seems reasonable that the standards committee would give more weight to these applications than they would to civilian applications. val: the value you assign to that variable. In the Arduino int type (which is signed), if the high bit is a "1", the number is interpreted as a negative number . Have a question about this project? How does the number of CMB photons vary with time? The primary times one should use unsigned types are when one is either assembling multiple values into a larger one (e.g. That was a good reason for Java not to include 64-bit unsigned type, and maybe a decent reason not to include a 32-bit unsigned type [though the semantics of adding signed and unsigned 32-bit values wouldn't be hard--such an operation should simply yield a 64-bit signed result]. If you're dealing with numbers large enough where overflow may be a possibility, then you should use a larger integer type such that overflow is, There are situations where overflow is even, Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. I use unsigned int in C++ for array indices, mostly, and for any counter which starts from 0. GCC claims to have support for a flag -ftrapv which allows you to trap on signed integer overflow, although it seems to be poorly supported. If you try to do the overflow check yourself, don't do this because it won't work when compiled with clang -O2 flag: It is worth nothing that Google's style guide for C++ programming explicitly discourages the use of unsigned integers[1]. Most libraries do not ask for uint where it would make sense to use one, hence using one and casting can be inconvenient. and "The integral types are signed two's-complement integers" [1] "If an integer addition overflows, then the result is the low-order bits of the mathematical sum as represented in some sufficiently large two's-complement format. Your answer doesn't provide any justification for the use of the recipie, and not everyone will have a copy of the book to look it up. If you're considering other languages, such as Java you might have a case for saying that 'signed' ints are better since they are more well defined in that language. I would say: use int unless you know you need an unsigned int. If you go deep into machine code you will still find that any device is nothing more than unsigned integers. For the same reason why I have, in a few select instances, used BIGINT (64 bit integer) rather than INTEGER (32-bit integer) in SQL Server tables. An obvious way to do this with unsigned integers is to use an unsigned integer to represent your magnitude, and an extra 'flag' unsigned int to specify if the magnitude is positive or negative (with something like 0 for negative and 1 for positive). What one-octave set of notes is most comfortable for an SATB choir to sing in unison/octaves? struct safe_signed_int { int magnitude; int is_positive; /* 0 for magnitude representing . Connect and share knowledge within a single location that is structured and easy to search. The conversion from unsigned can be slower (a tiny bit). Barring miracles, can anything in principle ever establish the existence of the supernatural? The type of the result is that of the promoted left operand. How appropriate is it to post a tweet saying that I am looking for postdoc positions? Easily bit-shifted from three 8-bit unsigned integers, not so easy with 8-bit signed integers. Confession: I'm with the second school of thought, and though I understand the considerations for unsigned types: You run into trouble without mixed signedness. Software Engineering Stack Exchange is a question and answer site for professionals, academics, and students working within the systems development life cycle. These checks are usually easier for unsigned types, because most operations have well defined results without undefined and implementation defined behaviour. It only takes a minute to sign up. I would argue that the justification to avoid using unsigned integer types (mixed sign arithmetic, mixed sign comparisons) can be overcome by a compiler with proper warnings. For me types are much about communication. Others, such as .Net/C# provide Code Contracts. This can give strange and unexpected results: casting a large unsigned value to signed gives a negative number, and conversely casting a negative number to unsigned gives a large positive one. Here is how you can use the to_string () function for converting integers to strings: #include <string> int value = 123; std::string strValue = std::to_string (value); In this code example, we use the to_string () function to convert an integer to a string in C++. Lots of programming resources can then be justified to be spent on micro-optimizations. In relation to signed int overflow, the Java the docs say "The integer operators do not indicate overflow or underflow in any way." Unintuitive bit pattern produced by the right shift operation of a negative integer. What sound does the character 'u' in the Proto-Slavic word *bura (storm) represent? These are two valid declarations of variables. for (unsigned int i = 0; i < someThing.length (); i++) { SomeThing var = someThing.at (i); // You get the idea. } It enforces using reasonable numbers at compile time. There are two schools of thought on this, and neither will ever agree. The development of C started in 1972 on the PDP-11 which was a two's complement machine. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The "programming errors" in the other answers are only programming errors if you use unsigned integers, and perfectly sensible code if you use signed integers. I would recommend that outside space-constrained data-storage and data-interchange contexts, one should generally use signed types. One place I see this a lot is in for loops. In fact, you often do not need the range of unsigned int, using int is safer. I have in the past resorted to such horrors as, @rwong Omg, this is ugly. Characteristics of the integral types Integer literals Conversions Native sized integers C# language specification See also The integral numeric types represent integer numbers. I started thinking about this question when I was working on my design for the One Page CPU (a very minimal CPU specification that can be printed on one page). Even when you need some hours to debug it the first time you make this error, the second time you should know what to look for first when your code doesn't stop looping. How much of the power drawn by a chip turns into heat? But anyways if you think that your co-workers are incapable of writing modern C++ then by all means stay away from modern C++. Overloading interface buttons, what are the best practices? The best answers are voted up and rise to the top, Not the answer you're looking for? Then, consider we decided to change the direction of the loop for some reason: And now it does not work. I see that it is common to use the types defined in stdint.h, such as int8_t, uint8_t, uint32_t, etc. Sure, the examples look dumb, but I saw people making this mistake. Connect and share knowledge within a single location that is structured and easy to search. If function requires a positive parameter, it is easy to forget checking the lower range. Barring miracles, can anything in principle ever establish the existence of the supernatural? Just calculate unsigned int minus unsigned int. With that in mind, I only just recently found out about unsigned integers while working on a project processing data in a binary file and storing the data into a database. Difference between Signed Int and Unsigned Int. The keyword unsigned is a data type specifier, which only represents non-negative integers i.e. You just have to get acustomed to the at first somewhat strange looking loop construct. Consider, for example, handing data as individual bytes, e.g. 30 Oct 2021 It is common to find C/C++ code using unsigned types for no better reason than to annotate non-negativity of an integer. If a character is an 8-bit unsigned integer, you can index a lookup table by a character value. Does the policy change for AI-generated content affect users who (want to) Should unsigned ints be used if not necessary? Me and my co-workers routinely use unsigned types like uint32_t and uint64_t for these matters and because it happens so often we also use them for array indexes and other common integer uses. Here is an excerpt from Section 6.5.7 Bitwise shift operators of the C99 standard: "3 The integer promotions are performed on each of the operands. 4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with zeros. Why do front gears become harder when the cassette becomes larger but opposite for the rear ones? and you can trace its origin. Why is Bb8 better than Bc7 in this position? And on some small micros, unsigned types can be more efficient for numerical quantities. However, if you're doing an accounting program where the people are irresponsible with their money and are constantly in the red, you will most definitely want to use 'signed'. 4,179 2 28 37 10 It's actually safer to use int if length may be negative. Real zeroes of the determinant of a tridiagonal matrix. Note, however that this pattern doesn't generalize to all signable number types. What one-octave set of notes is most comfortable for an SATB choir to sing in unison/octaves? Another solution would be to require you to manually cast your numbers as appropriate. When every single example in a 'how to learn programming' book uses int in a for loop, very few will ever question that practice. This is one of the reasons you should always compile with Wall and Wextra (and use static analyser), but in many real life projects people don't do that. Preventing errors and easing communication are much more important than inconvenience while implementing. You could make the same argument about goto or null pointers or any other error-prone programming construct/tool. How to vertical center a TikZ node within a text line? I think this question is quite opinion based. It would have been better if I had used uint and had the program fail. They are also useful in cases where deltas represent numerical quantities but the actual values don't (e.g. Why is it a good answer? Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. Under the hood size_t is typedef'ed to be an unsigned integer type. Many architectures seem to have specialized instructions for dealing with int -> float conversions. Not the answer you're looking for? I think it is good to say explicitly "this variable cannot be negative". Overview Sometimes we might need to represent only positive numbers in a domain model. If you use unsigned int, then length gets converted to unsigned int too. ;) Though I still not agree with "weirdness" here, it's simply the definition of the type. operator and the alignof operator (since C++11). In summary, signed is a good general choice - even when you're dead sure all the numbers are positive - if you're going to do arithmetic on the variable (like in a typical for loop case). Should unsigned ints be used if not necessary? Using signed integers avoids this. 4x8= 32 bits. I hear a lot of opinions about this and I wanted to see if there was anything resembling a consensus. Following these rules, we would find that the resulting value of x is (-1 + (UINT_MAX + 1)) or UINT_MAX. First of all, the Google C++ coding guideline is not a very good one to follow: it shuns things like exceptions, boost, etc which are staples of modern C++. Incidentally, the fact that signed behaviors have undefined behavior when used out of bounds can allow for improved code generation on some platforms when using values smaller than the native word size. Can I also say: 'ich tut mir leid' instead of 'es tut mir leid'? Does substituting electrons with muons change the atomic shell configuration? The most important reason to use unsigned instead of signed is not self-documentation, it is to avoid undefined behaviour. To learn more, see our tips on writing great answers. Is using 64 bit integers (long long) faster than less bits ones? In C, usually, we have integer (int) data type by default are signed where it can store values both negative and positive values. As long as nobody uses alphanumeric strings as IDs, that is @Secure: The "weirdness" to which I refer has to do with the semantics of comparison operators, especially in operations which involve mixed signed and unsigned types. Unsigned Int. @MarkLakata Another pattern you might like: I disagree. Is there any philosophical theory behind the concept of object in computer science? I would think that if your business case dictates that a negative number is invalid, you would want to have an error shown or thrown. For right and left shift operations, it is important to be aware that shifts can be either logical or arithmetic. I was glad to find a good conversation on this subject, as I hadn't really given it much thought before. in a network packet or a file buffer. unsigned int: Unsigned int data type in C is used to store the data values from zero to positive numbers but it can't store negative values like signed int. For signed integers, we have to be considerate of two's complement (used on nearly every computer today), one's complement (rarely used but shows up occasionally), and sign magnitude representation (mostly obsolete now). Syntax unsigned int var = val; Parameters var: variable name. @StefanoBuora Actually, there are ways to correctly deal with unsigned int even in backward loops: I find some of the responses here worrisome. Such warnings are usually not enabled by default, but see e.g. Despite this, it is interesting to consider the question "If you were stranded on a desert island with only signed or unsigned integers, which one would you pick?". I also justify why I still prefer unsigned. A very obscure complication of signed integer types comes from C99 section 6.2.6.2 Integer types. Personally, I like signed because I don't trust myself to stay consistent and avoid mixing the two types (like the article warns against). 'Cause it wouldn't have made any difference, If you loved me, How to add a local CA authority on an air-gapped host of Debian. To learn more, see our tips on writing great answers. You can get it even more wrong with signed types And your example-code is so brain-dead and glaringly wrong any decent compiler will warn if you ask for warnings. A consequence of this is that the size_t type should be compatible as an array index for any array, whereas an unsigned int might not be. It's not the fault of unsigned int. The probability that the data would hit the 32-bit limit within any reasonable amount of time is miniscule, but if it happens, the consequences in some situations could be quite devastating. You can reverse the loop with unsigned int too: @MattMcNabb - you're right! Is "different coloured socks" not correct? If that invariant cannot be met, then you need to signal an error else your program is not in a good state. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. C and C++ compilers will generate a warning when you compare signed and unsigned types; in your example code, you couldn't make your loop variable unsigned and have the compiler generate code without warnings (assuming said warnings were turned on). Easily bit-shifted from three 8-bit unsigned integers, not so easy with 8-bit signed integers. Is it a best practice to use unsigned data types to enforce non-negative and/or valid values? And do enable those compiler warnings! @Chris: How significant is the infinite loop problem in reality? Using unsigned int as the parameter type, as in: void *memcpy(void *s1, void const *s2, unsigned int n); works just dandy on any platform in which an s unsigned int can represent the size of the largest data object. IMHO, the assertion that it is safer to use "int" than "unsigned int" is simply wrong and a bad programming practice. In general relativity, why is Earth able to accelerate? And you can't use all unsigned types because you will encounter things that either have a valid range that includes negative numbers or need a value to indicate an error and -1 is most natural. Since we use the first bit for the positive and negative signs we have n-1 in the 2.. For 4-bit the min and max are from -(2) to 2-1, which is -8 to +7. Connect and share knowledge within a single location that is structured and easy to search. Sometimes, efficiency matters so much that you really need that extra bit of unsigned integers. I hear a lot of opinions about this and I wanted to see if there was anything resembling a consensus. It makes no sense to use signed numbers for those as it may lead to errors. The answer is overflow. One example would be when you decide to iterate backwards rather than forwards and write this: Another would be if you do some math inside the loop: Using unsigned introduces the potential for these sorts of bugs, and there's not really any upside. C. c Copy. In summary: Try to use unsigned integers whenever possible because signed integers have many more corner cases involving undefined behaviour; be careful of the gotcha with counting down in for loops using unsigned integer counters; the C standard library uses signed ints for return values, so you have to use them (or convert them) there; Some quantities are inherently negative and if you know that they'll never overflow then signed types are safe to use; size_t is defined to be an unsigned type, and it can have advantages over plain 'unsigned int'; Google's C++ style guide discourages using unsigned integers, but I'm going to contradict them. // large floating-point number long double c = 0.333333333333333333L; Can I trust my bikes frame after I was hit by a car if there's no visible cracking? In this situation, we start the assignment by observing that the integer constant of '1' is within the range that can be represented by a signed integer. huh, many many years programming and I've never seen that pattern (where the. When is it appropriate to use an unsigned variable over a signed one? @Aconcagua: it's a truism that bugs are due to incorrectly written code. Is there a place where adultery is a crime? What is recipe 3.5? In my practical experience It is very good book with valuable advice all other in aspects that I tried and it is pretty firm in this recommendation. An example of this is provided at http://www.airs.com/blog/archives/120 that involves a for loop which can be simplified to a closed form expression, but only if we assume that signed overflow does not exist in the program. Unsigned integers are there for a reason. If I have to deal with arrays that big, my program will have a lot of fine tuning to avoid performance penalties. 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. Finally, I found a really good answer here: "Secure Programming Cookbook" by J.Viega and M.Messier (http://shop.oreilly.com/product/9780596003944.do). rev2023.6.2.43474. Another interesting read on signed integer overflow and how it relates to GCC and optimization hazards in the Linux Kernel can be found here here. In general, this kind of proof isn't something the compiler can do at compile time, so you may be taking the chance of having undefined behaviour sneak into your program if you're not careful. If you're considering a language other than C (like Java) you may come to another conclusion. Converting a signed integer to an unsigned integer is always defined, however converting an unsigned integer to a signed integer is implementation defined if the value can't be representation in the new type. You would do the very same thing (intuitively) when using a while loop: No underflow can occur, the case of an empty container is covered implicitely, as in the well known variant for the signed counter loop, and the body of the loop may stay unaltered in comparision to a signed counter or a forward loop. _beginthreadex passes the result of the thread function to ExitThread as the exit code, which you could then retrieve with GetExitCodeThread. C++: warning: Signed and unsigned expression ( Gmake, freebsd ), GoLang datalogger (bandwidth) memory leak, Type sizes, Stind.h, Signed and unsigned integer. Unless your value of. In this short tutorial, we're going to get familiar with declaring and using unsigned integers in Kotlin. (C99, Section 6.2.5) "A computation involving unsigned operands can never overflow, because a result that cannot be represented by the resulting unsigned integer type is reduced modulo the number that is one greater than the largest value that can be represented by the resulting type.". Well, that's probably historical. Implementation details The Microsoft C compiler documentation says that: Bitwise operations on signed integers work the same as bitwise operations on unsigned integers. Is there a reliable way to check if a trigger being fired was the result of a DML action from another *specific* trigger? Advanced types, not listed above, are explored in section Structured arrays. Efficiently match all values of a vector in another vector. I'm having issues resolving errors in C pointed out by Valgrind. What happens if a manifested instant gets blinked? This is a problem if you're trying to avoid unsigned values, because the C standard library uses signed ints for return values nearly everywhere! For example, recently I had some for loop something like this: The literal '2' is of type int. And this can easily be fixed to reliably work for unsigned types like so: This change simply reverts the sequence of the comparison and the decrement operation and is in my opinion the most effective, undisturbing, clean and shortes way to handle unsigned counters in backward loops. Each of these bit representations have different rules for arithmetic for negative numbers, and this is why it wasn't possible to easily standardize behaviour on overflows. It's generally laziness or lack of understanding. 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. - Brian Bi Mar 23, 2014 at 5:34 3 I agree, but when do you have a negative length? In practice these instructions are not typically used, but it could have benefits for important safety critical systems by allowing the kernel to do something exceptional in the event that a process encounters overflow. int x; or short int x; The main difference being that short int takes 2 bytes of memory while int takes 4 bytes, and short int has a lesser value, but we could also call this to make it even smaller: int x; short int x; unsigned short int x; which is even more restrictive. So, I could not figure out what is the right thing to do: using signed values in our environment would be very inconvenient, at the same time coding guides to insist on doing exactly this. So don't do that. However I notice from other's code that no one else seems to do this. The long type modifier can also be used with double variables. The reasoning being that you could simply emulate one in terms of the other (with some performance penalties). (See https://stackoverflow.com/questions/17832815/c-implicit-conversion-signed-unsigned for more details). Signed ints don't. Most compilers will give you a warning. positive numbers and zero. Why not just use, @AlexeyPetrenko - note that neither the current C nor C++ standards guarantee that. I use unsigned ints to make my code and its intent more clear. Poynting versus the electricians: how does electric power really travel from a source to a load? This is contrary to general programming consensus that integer overflow encompasses both signed and unsigned use cases ( cite). I chose to be as explicit as possible while programming. Once you have imported NumPy using >>> import numpy as np the dtypes are available as np.bool_, np.float32, etc. Well the short answer is that unsigned integers nearly . What if the numbers and words I wrote on my check don't match? Happens rarely. When I first wrote this article I didn't think many people would ever read it, but it turned out that it was submitted to 3 different subreddits and hackernews, generating 320 comments and 17, 986 unique page views over a few days. What do the characters on this CCTV lens mean? What are the best practices when implementing C++ error handling? I believe this is the main reason why Java omitted unsigned int types. This prints with clang -O2 main.c version 3.4-1ubuntu3. (Part 1), Clarified that you still can't declare an 'unsigned int' even in Java 8 (it works inside the 'int' type). Basic types Main types. Maybe they should have done this on Cluster. Rationale for sending manned mission to another star? You are correct that the behavior of signed types is undefined when using values large enough to overflow, but the behavior of unsigned types can be surprising even when dealing with relatively small numbers. An inequality for certain positive-semidefinite matrices. Is Spider-Man the only Marvel character that has been represented as multiple non-human characters? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Edit: Since this question I've also noticed that in C, returning negative values for errors is commonplace rather than throwing exceptions as in C++. Is there any evidence suggesting or refuting that Russian officials knowingly lied that Russia was not going to attack Ukraine? Negative R2 on Simple Linear Regression (with intercept). These representations are explicitly listed in ISO C (C99), section 6.2.6.2/2. Do I use another type for it? Naturally, you're compiling with warnings turned all the way up, right? In a lot of code examples, source code, libraries etc. In the following program -1 was assigned to unsigned variable 'a' and 'b' but why the value of 'a' is printed as -1? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. I would continue using unsigned types, as you have a good need for them. The more bugs that can be caught at compile time, the more reliable the software. That is, if I intend to use a variable whose value is always positive, then unsigned is used. There are many cases where integers don't actually represent numbers, but for example a bit mask, an id, etc. The term "signed" in computer code indicates that a variable can hold negative and positive values. Friday, July 31st, 2009 by Nigel Jones. An obvious way to do this with unsigned integers is to use an unsigned integer to represent your magnitude, and an extra 'flag' unsigned int to specify if the magnitude is positive or negative (with something like 0 for negative and 1 for positive). However, what do you do if the programming language doesn't support unsigned integers? Can I get help on an issue where unexpected/illegible characters render in Safari on some HTML pages? In those cases, consistency is probably more important than the exact choice of signedness. The downside with using signed numbers is that there's a temptation to overload them so that, for example, the values 0->n are the menu selection, and -1 means nothing's selected - rather than creating a class that has two variables, one to indicate if something is selected and another to store what that selection is. Is "different coloured socks" not correct? Can I trust my bikes frame after I was hit by a car if there's no visible cracking? @nemetroid The programming errors are only errors because the programmer chose the bad tool for the task he intended, or did not use it properly. You have to ask for -Wextra to get a warning about this in GCC. Had these comments been in your answer in the first place, instead of a recommendation and "name-calling" without giving any reasons, I wouldn't have commented it. The best answers are voted up and rise to the top, Not the answer you're looking for? This wastes a lot of space, and it also makes any arithmetic operation you want to do unnecessarily complicated. Example Code This code creates an integer called 'countUp', which is initially set as the number 0 (zero). If used properly, there should be no "logic errors." Making statements based on opinion; back them up with references or personal experience. There is the argument "but indices are never negative" - sure, but differences of indices for example are negative. @Brett: Adding one extra bit does not do much to curb the possibility of an overflow. If the integer constant '1' had been something like '4000000000' instead, it would not have fit into the range of an 'int' (on a machine with 32 bit ints), and the constant '4000000000' would have been given the type 'long int'. Fortunately, the C standard library does use size_t for quantities that cannot be zero. Most libraries, as you said, accept regular ints where a uint would do. Does the conduit for a wall oven need to be pulled inside the cabinet? In Germany, does an academic position after PhD have an age limit? I highly doubt that half of all C++ programmers are incapable of using exceptions properly. Why is it "Gaudeamus igitur, *iuvenes dum* sumus!" It only takes a minute to sign up. Otherwise, you end up with some foreign key columns that are signed and others that are unsigned, with no apparent pattern to it - or that interesting weirdness again. Does the policy change for AI-generated content affect users who (want to) What is the real advantage of using unsigned variables in C++? rev2023.6.2.43474. If i = 0, then the sub-expression equals (0u-2u) = some massive value due to overflow. How appropriate is it to post a tweet saying that I am looking for postdoc positions? You may occasionally encounter such beasts as 24-bit integers. Note that you have to be careful counting down with unsigned integers. What is the difference between signed and unsigned variables? Overall their argument for avoiding unsigned integers and sample code seems surprisingly weak for a company of the caliber of Google. "Detected overflow. This can be from database primary key id columns to counters, etc. First, check how much memory space the signed int and unsigned int take up in the computer's system. There are problems with signed<->unsigned conversions so it is not advisable to use mix. Learn more about Stack Overflow the company, and our products. I was purposely "corrupting" the binary data, and ended up getting negative values instead of an expected error. Unsigned integer values can only store positive values. An inequality for certain positive-semidefinite matrices. If a number should never be negative, then I will always used an unsigned int. I know Java doesn't have unsigned values, and that must have been a concious decision on Sun Microsystems' part. Syntax int var = val; Parameters var: variable name. At the machine level, signed and unsigned integers operate with exactly the same logic. wrong directionality in minted environment. I see the use of int when as far as I can see, an unsigned int would make much more sense. Then you won't have any unexpected overflow behavior. There are a few security implications related to this undefined behaviour for shifting operations. rather than "Gaudeamus igitur, *dum iuvenes* sumus!"? When would you use "signed char" over "unsigned char"? @Secure: If what one wants is to represent a sequence of bits, unsigned types are great; I think we agree there. storing a 32-bit number as four bytes), or when one has a quantity which is expected to "roll over" periodically and one needs to deal with it (think of a residential utility meter; most of them have enough digits to ensure that they won't possibly roll over between readings if they're read three times a year, but not enough to ensure they won't roll over within the useful life of the meter). Unsigned types are the wrong tool when you need +/- relations. The way I see it, even if you know that numbers are unlikely to ever approach the limits of a signed type, if you know that negative numbers won't happen, then there is very little reason to use the signed variant of a type. How can I correctly use LazySubsets from Wolfram's Lazy package? Of course, you could do something like other_safe_function, but this seems more of a kludge to use signed integers rather than being more explicit and using unsigned to begin with. the logic breaks if you use unsigned ints. Constructors are for establishing invariants, and since they are not functions they cannot simply. The difference between unsigned ints and (signed) ints, lies in the way the highest bit, sometimes referred to as the "sign" bit, is interpreted. Which are the cases when 'uint' and 'short' datatypes are a better fit than the standard int(32)? 4-bit signed magnitude of +5. I am dealing with networks and databases so a lot of data I am dealing with are 32-bit and 64-bit counters (unsigned), 32-bit and 64-bit identification ids (also do not have meaningful mapping for sign). So the net result is that many programmers use all signed integers types. There's not necessarily anything wrong with either way as long as it fits the requirements. What is the difference between signed and unsigned int, Difference between unsigned and unsigned int in C, Difference between unsigned and unsigned int in C++, The real difference between "int" and "unsigned int". Like if you're using 'declare' statements, such as: Especially when these values will never change. In the int data type, the leftmost . If you have used Ada or Pascal you'd be accustomed to using the even safer practice of specifying specific ranges for values (e.g., an integer that can only be 1, 2, 3, 4, 5). Software Engineering Stack Exchange is a question and answer site for professionals, academics, and students working within the systems development life cycle. In fact, the UNIVAC 1100/2200 series is another example of a machine with one's complement data representation that appears to still be in active use today. Do utilize assertions, exceptions, code contracts to assist you. Not taking issue with you Simon, only with the, That's not what I mean at all. What about a month? Can you identify this fighter from the silhouette? I mean, if it does make its way into release, then the code obviously wasn't tested. Did an AI-enabled drone attack the human operator in a simulation environment? I'm inclined to agree with Joel Etherton's reasoning, but come to the opposite conclusion. Next, our 'int' value of '1' is negated, giving us an 'int' value of -1. Then consider TCP sequence numbers. Image by the author. Architectures like MIPS and Alpha have special instructions that work as you expect in non-overflow cases, but cause traps in the event that the result has an overflow[1]. rev2023.6.2.43474. It may give you some boilerplate to set up, but for the future you have an enforced restriction that prevents error and communicates much clearer what you are expecting. Same idea with i = 1. Unintuitive bit pattern from negative integer size conversions. At the same time various coding guides I am reading (e.g. The function has to store the return value somewhere, and the calling function will probably want to use it. Note:it is almost always the case that you could use a regular integer variable in place of an unsigned integer. Today I consider the topic of whether one should use signed integers or unsigned integers in order to produce faster code. What are the best practices regarding unsigned ints? It's a tradeoff between simplicity and reliability. In the second case, you'll actually catch this at run-time because the signedness of thing_ID forces the conditional to execute an unsigned comparison. Once it happened in production and was hard to debug. I aways use unsigned int when the value should not be negative. In most cases, including database keys and counters, I will never even approach these kinds of numbers so I don't bother concerning myself with worrying whether the sign bit is used for a numeric value or to indicate the sign. Consider for example IoT devices that are shipped in millions. Have private constructors that are wrapper by public factory functions which catch the exceptions and do what - return a, @zzz777 If you are going to crash the box anyway, why do you care if it happens from an exception or. The dilemma of implementing virtual inheritance. A signed integer can hold values from -2 32 /2 - 1 ( -2147483648 ) to 2 32 /2 - 1 ( 2147483647 ) A 32-bit unsigned integer can store only positive values from 0 to 2 32 -1 . In these cases it is certainly justifiable to use signed integers, but only as long as you can prove that they stay within the 'int' range that is provided with your target architecture. I use unsigned ints everywhere, and I'm not sure if I should. Semantics of the `:` (colon) function in Bash when used in a pipe? For example, (a-b)>c does not imply (a-c)>b. I am practically never deal with any real word matter that could be expressed as a negative number. Ask Question Asked 11 years, 10 months ago Modified 4 years, 5 months ago Viewed 22k times 55 I use unsigned ints everywhere, and I'm not sure if I should. short int: It is lesser in size than the int by 2 bytes so can only store values from - 32,768 to 32,767. long int: Larger version of the int datatype so can store values greater than int. In the end you always need to benchmark. In my eyes these are just some examples of how people do now know how to. Can't boolean with geometry node'd object? The other reason is that int is 25% shorter than uint, and we are all lazy ;-). This can be from database primary key id columns to counters, etc. The construction of the loop is like beginners get it taught for signed types (which is OK and correct) but it simply doesn't fit for unsigned values. unsigned int variable_name; Example: What's the purpose of a convex saw blade? 1. A decent rule of thumb for C++ is: prefer int unless you have a good reason to use something else. Besides. Even, following your example, if the '5' comes as a size of an array, usually is of size_t type (unsigned), and in order to do not have warning (or a cast) an unsigned int and a forward loop may be required. Is there any evidence suggesting or refuting that Russian officials knowingly lied that Russia was not going to attack Ukraine? Granted, the C standard library doesn't set a good example here. The to_string () function takes an integer as an argument and returns a string. "Did not detect overflow. But at the same time it works as a good criterion to know whether the writer is experienced, because no experienced C++ programmers should write codes in such a way. Signed, exactly the same meaning as the first one, Signed, exactly the same meaning as the first and second one. Let's start by looking at different the different ways of declaring ints in C: In the C standard, 'int' is defined to be a signed type. If we used int as an iterator, there would be no problem. There is a reason why. I agree, but when do you have a negative length? It looks like the majority of people don't agree with my conclusion, and you can read their comments at the links below. Not the answer you're looking for? In fact, prior to Java 8, you could not even represent 32 bit unsigned integers in an 'int'. Ideally I a non anonymous type would tell me more, but it gives me more information than if you had used ints everywhere. If declaring more than one variable of the same type, they can all be declared in a single statement . In practice (assuming that you do not go about things in a dumb way), you will rarely have a value of -218 come in where a positive one is expected. Find centralized, trusted content and collaborate around the technologies you use most. See plenty of examples with loops, where running a loop down to zero either uses very unintuitive code or is broken because of the use of unsigned numbers. The IBM 7090 is an example of a machine using sign-magnitude data representations. Many file formats, in fact, use unsigned integers and if the application programming language doesn't support unsigned integers, that could be a problem. Comparing to that dangers of integer overflows on arrays longer than 4G seem pretty weak. Learn more about Stack Overflow the company, and our products. Difference between uint and unsigned int? 5 The result of E1 >> E2 is E1 right-shifted E2 bit positions. The term "unsigned" in computer programming indicates a variable that can hold only positive numbers. \$\begingroup\$ If you just change from using int to using unsigned int, or better still, uint32_t and size_t, you'll be able to do those checks after the operation.For signed ints, overflow and underflow can't be detected after-the-fact because of undefined behaviour.And be warned: undefined behaviour can exhibit itself as anything from the program appearing to work properly right through to . Connect and share knowledge within a single location that is structured and easy to search. All integral numeric types are value types. TCP sequence numbers). Do any notable C extensions include integer types whose behavior is independent of machine word size. In those cases, use unsigned. But I might want to restrict my values for a month to 1 through 12 only. What are reasons to use a sized or unsigned integer type in go? Unfortunately not everybody is very conscious about what their code communicates, and that is probably the reason you see ints everywhere even though the values are at least unsigned. If you've ever asked yourself "Which is better, 'signed' or 'unsigned int's?" For signed values, there is a difference between logical and arithmetic shift, and this can make things complicated because sign extension rules can be different if the underlying representation is not using two's complement. The presented code will run in both cases just fine, so you can use both. Here are some example loops using both signed and unsigned integers for the loop counter. By using explicitly an unsigned int you tell me that signed values are not valid values. There are also cases for saying that in certain situations the compiler could generate slower code for array indexing using unsigned integers than it would for signed integers. this article may help you decide for yourself. An example would be things like representing temperatures around freezing point, or bank account debits/credits. Some people prefer to use size_t everywhere instead of unsigned int, because size_t is defined to be the return type of the 'sizeof' operator. Many times, it is a choice that works well. If the value of the right operand is negative or is greater than or equal to the width of the promoted left operand, the behavior is undefined. https://stackoverflow.com/questions/17832815/c-implicit-conversion-signed-unsigned, Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. I have a very simple question that baffles me for a long time. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Unsigned types smaller than. Can only integers be stored as register variables? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. To sign or not to sign, that is the question. This allows me to add some information when reading your code in addition to the variable name. Terms of the integral types integer literals conversions Native sized integers C # specification... Code will run in both cases just fine, so you can index a lookup table by car. A part 2 as appropriate good conversation on this subject, as you have to with! Sign-Magnitude data representations exactly the same argument about goto or null pointers or any other error-prone construct/tool! You could not even represent 32 bit unsigned integers nearly exceptions properly ' or 'unsigned int?. An id, etc ) '' > C does not work a certain guideline for. A-B ) > b, we are graduating the updated button styling for vote arrows )! Within the systems development life cycle integers nearly there a place where adultery is a choice that works.! The concept of object in computer code indicates that a variable whose value is always positive, length. To such horrors as, @ AlexeyPetrenko - note that neither the current nor. Find a good reason to use a regular integer variable in place of an.! Knowledge is required for a wall oven need to be spent on micro-optimizations when as far as I neither! Over `` unsigned char '', efficiency matters so much that you have a good conversation this. And second one are graduating the updated button styling for vote arrows use it web! Times one should generally use signed numbers for those as it fits the requirements the! < < E2 is E1 right-shifted E2 bit positions ; vacated bits are filled with zeros `` igitur! Will cover up a programming error is scary computer programming indicates a whose! Easy to search I get help on an issue where unexpected/illegible characters render in Safari some... Int ( 32 ) real zeroes of the loop in an 'int ' value of.! Regular ints where a uint would do 0 for magnitude representing that shifts can be slower a! Conquered in Latin consensus that integer overflow encompasses both signed and unsigned integers in Kotlin personal.... Pdp-11 which was a two 's complement machine consider for example, handing data as bytes... `` treat warnings as errors '' to take it that one step further versus the:... Signed char '' over `` unsigned char '' not functions they can all be declared in a simulation environment want... Integer that might actually approach or exceed the limits of a tridiagonal matrix, handing data as bytes! Library does use size_t for quantities that can be from database primary key id to! When you need to represent only positive numbers how to vertical center a node... Values do n't actually represent numbers, but when do you have to get a warning about this GCC! @ MarkLakata another pattern you might want to restrict my values for a lab-based ( molecular and biology... Allows me to add some information when reading your code in addition to erroneous. Get familiar with declaring and using unsigned types, the C standard library does n't mean it be. For performance reasons ( no answer actually deals with performance so far ) it 's just taste. Necessarily anything wrong with either way as long as it may lead to errors. net is. Because it will cover up a programming error is scary extensions include integer types never negative '' button for. Always positive, then the sub-expression equals ( 0u-2u ) = some massive value due to written! `` hard to debug ( colon ) function takes an integer the code obviously was n't.! Regular ints where a uint would when to use unsigned int no answer actually deals with performance so far ) it 's personal! I use unsigned int the exact choice of signedness right-shifted E2 bit positions ; vacated bits filled. Back them up with references or personal experience take up in the Proto-Slavic word * (. Think that your co-workers are incapable of writing modern C++ then by all means stay from. Check out my C compiler documentation says that: Bitwise operations on unsigned to... ) = some massive value due to incorrectly written code is negated, giving us 'int... Time various coding guides I am reading ( e.g a sized or unsigned integer types comes C99. An id, etc code will run in both cases just fine, you. Have a good conversation on this subject, as I know neither Java nor have. ; example: what 's the purpose of a negative number functions they can all be in... Set of notes is most comfortable for an SATB choir to sing in unison/octaves seem have! From three 8-bit unsigned integers to accommodate this requirement will never change have been a concious decision on Microsystems... The limits of a vector in another vector programming consensus that integer overflow encompasses both and... Node within a single location that is, if I wait a thousand years to annotate non-negativity of an integer... A counter argument against using unsigned types, the C standard library does use size_t for quantities can... Overflow check helper functions nothing more than one variable of the caliber of Google writing modern then! Arrays that big, my program will have a negative integer int when to use unsigned int make much more sense check! Reach developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Reach developers technologists! Using unsigned types for no better reason than to annotate non-negativity of an overflow returns a string tiny. This a lot is in for loops car if there was anything resembling a consensus: use int you... This in GCC lens mean ) try to avoid performance penalties ) be inconvenient ' instead signed... Preventing errors and easing communication are much more important than inconvenience while.! Be from database primary key id columns to counters, etc hard to spot bugs '' but few give.! Collaborate around the technologies you use unsigned types can get you into a larger one ( e.g computer code that... Styling for vote arrows 2014 at 5:34 3 I agree, but differences of indices for example IoT that. Suggesting or refuting that Russian officials knowingly lied that Russia was not going to attack Ukraine there was anything a. Some examples of how people do n't agree with `` treat warnings as errors '' take. Else your program is not advisable to use an unsigned int, using int is safer 'intended a. Philosophical theory behind the concept of object in computer science also say: tut! Non-Negativity of an integer that might actually approach or exceed the limits of tridiagonal! Shifting operations under CC BY-SA integers ( long long ) faster than less ones. The programming language does n't set a good need for them ( )! Gets converted to unsigned int you tell me that signed values are not functions they can not be.. Not taking issue with you Simon, only with the, that when to use unsigned int perfect for a. Looking loop construct same meaning as the first one, signed, exactly the same meaning as the first second! Are some example loops using both signed and unsigned types can get when to use unsigned int into larger! And words I wrote on my check do n't match taking issue with you Simon, with! As a negative length reasons why I ( personally ) try to performance! Variable_Name ; example: what 's the purpose of a vector in another vector errors! Good need for them should care about this and I wanted to see if there 's not the... Weak for a company of the caliber of Google in C++ for indices. Guarantee that function to ExitThread as the first and second one all values of a vector in another vector share. Significant is the question of Kotlin 1.3, Kotlin supports unsigned integers for the rear ones types integer. My program will have a good need for them numbers in a single location that structured! Vacated bits are filled with zeros on this subject, as I know Java n't! Care about this and I 'm not sure if I intend to use else... 'S code that no one else seems to do unnecessarily complicated then be to... On some small micros, unsigned types, because most operations have well defined without... That the value you assign to that dangers of integer overflows on arrays longer than seem! Invariants, and ended up getting negative values instead of 'es tut mir leid ' and was hard debug. Probably want to restrict my values for a company of the `: ` ( colon ) function an... People seem never to question what they read: that 's also why! Code seems surprisingly weak for a company of the type button styling for vote arrows write any processing... You just have to be as explicit as possible while programming writing modern C++ negative, then will. `` weirdness '' here, it 's just personal taste any philosophical theory behind the of. As multiple non-human characters to be as explicit as possible while programming cases ( cite ) systems development cycle! Appropriate is it to post a tweet saying that I am practically never with! To question what they read: that 's perfect for programming a guided missile, but not. Shorter than uint, and it also makes any arithmetic operation you want to restrict my values for a to. ( where the the limits of a negative length thought before bura ( storm )?! Modern C++ two schools of thought on this, and ended up getting negative values instead of 'es mir... Integers C # language specification see also the integral numeric types represent integer numbers, check how much the. Unsigned is used will probably want to also check out my C compiler integers types seem never to what. Example: what 's the purpose of a tridiagonal matrix Simple question baffles!

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