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Code Reviews

Welcome to Software Development on Codidact!

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Posts tagged c

13 child tags

Use this tag for questions concerning use of the C programming language and for questions containing code in the C language. Avoid using it together with the C++ tag unless your question is explicitly about code compatibility or differences between C and C++.

Unless the question explicitly mentions which version of the C standard that is uses, the current active version of ISO 9899 is assumed (C17/C18).

When applicable, always include information about which compiler and target system you are using.
Tag Wiki

The C language is a general-purpose programming language developed by Dennis Ritche at Bell Labs in the early 1970s. The original purpose was kernel- and application programming for the UNIX operative system, which is why many of the standard functions and libraries in C originate from UNIX.

In the 70s and 80s, there was no formal standardization of C. The closest thing to a canonical source was the book The C Programming Language, written by Brian Kernighan and Dennis Ritchie. The book is referred to as "K&R" (Kernighan & Ritchie) and everything before standardization is therefore usually called "K&R C".

The first standardization of the language was carried out in USA, by ANSI in the year 1989. This first version is therefore widely known as "ANSI C". One year later in 1990, the ANSI standard was adopted internationally by ISO, why this version of the language is also often called "C90". Technically, "ANSI C", "C89" and "C90" are identical.

The language standard has since then been revised several times:

  • a minor revision in 1995 ("C95")
  • a major revision in 1999 ("C99")
  • a major revision in 2011 ("C11")
  • a minor revision in 2017 ("C17" or "C18", since it was released by the committee in 2017 but published by ISO in 2018).

These revisions are typically backwards compatible, but modern C code will not run on older compilers. C17 is the current standard. The C language is technically owned by ISO and it is maintained by the ISO committee JTC1/SC22/WG14.

The formal name for the standard is ISO/IEC 9899 - Information technology - Programming languages - C. Draft versions of the C standard are usually available free of charge, such as draft N1548 of C11.

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Q&A Testing an opaque type's internals

First: What is an opaque pointer in C? Now when it comes to testing such a type, I know of 3 ways: Include the source file (the one containing the definition of the type and the functions tha...

2 answers  ·  posted 5d ago by Melkor-1‭  ·  last activity 4d ago by John C‭

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Q&A How can I manage multiple consecutive strings in a buffer (and add more later)?

This question is inspired by If I have a char array containing strings with a null byte (\0) terminating each string, how would I add another string onto the end? on Stack Overflow. Suppose I have...

2 answers  ·  posted 2mo ago by Karl Knechtel‭  ·  last activity 18d ago by Lundin‭

Question c string
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Q&A Can I access an array element from a pointer to an object contiguous with but outside the array?

C prohibits accessing an array out of bounds even if measures were taken to ensure that what should lie outside those bounds were known: struct MyStruct { int x[2]; int y, z; }; static...

1 answer  ·  posted 2mo ago by CPlus‭  ·  last activity 1mo ago by Lundin‭

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Code Reviews Pattern / architecture for interfacing with components in C

I'm working on the architecture, where the assumption is to easily extend the options in the system and also to provide some kind of encapsulation (from the main we could only access the type1 / ty...

1 answer  ·  posted 2mo ago by patriko8520‭  ·  last activity 2mo ago by Lundin‭

Question c architecture
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Q&A Is strcpy dangerous and what should be used instead?

I heard rumours that the strcpy function is dangerous and shouldn't be used. Supposedly it can be exploited to create buffer overflows somehow. And indeed when I compile my C code in the admittedl...

2 answers  ·  posted 3y ago by Lundin‭  ·  last activity 2mo ago by Lundin‭

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Code Reviews A small header-only input output library

The library (inspired by stb libraries) attempts to provide some commonly used functions (reading a file into memory, determining the size of a file) that are missing from the C standard library po...

0 answers  ·  posted 3mo ago by Melkor-1‭  ·  edited 2mo ago by Melkor-1‭

Question c string input output
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Q&A Are there technical reasons to pick one struct coding style over the other?

C offers two different styles when it comes to structs (and union/enum too). Either declare them using a struct tag only ("struct tag style"): struct my_type { ... }; struct my_type x; Or ...

1 answer  ·  posted 3mo ago by Lundin‭  ·  last activity 3mo ago by Lundin‭

Question c code-style struct
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Code Reviews Trie Implementation, Graph Visualization and Auto-Completion in C

Given a list of strings (say a text file containing some C symbols: c-symbols.txt), the program can: Generate a graph of the underlying trie (-p/--prefix can be specified to inspect a specific ...

1 answer  ·  posted 3mo ago by Melkor-1‭  ·  last activity 3mo ago by Lundin‭

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Q&A What is the purpose of having underscored names and then defining a non-underscored alias to it?

In a C implementation in <stdio.h> on Linux I saw something like: extern FILE *__stdinp; extern FILE *__stdoutp; extern FILE *__stderrp; And then: #define stdin __stdinp #define stdou...

1 answer  ·  posted 6mo ago by 90 98‭  ·  last activity 6mo ago by aghast‭

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Q&A What is do { } while(0) in macros and should we use it?

Background I can see the need to use { } when implementing a function-like macro such as this one: #define HCF(code) fprintf(stderr, "halt and catch fire"); exit(code); Because if we use the f...

2 answers  ·  posted 3y ago by Lundin‭  ·  last activity 6mo ago by Karl Knechtel‭

Question c code-style macros
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Q&A When should I parenthesize macro arguments in C?

I've seen macros use parentheses to enclose its arguments. Most of these make sense, as in #define sum(a, b) ((a) + (b)) The outer prevents the following: #define sum_bad(a, b) (a) + (b) ...

2 answers  ·  posted 6mo ago by alx‭  ·  last activity 6mo ago by Lundin‭

Question c macros
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Q&A What is the meaning of "short circuit" operators?

When reading about various operators used by programming languages, the term "short circuit behavior" is often used. For example in this C code: int a = 0; a && b++ Someone explained t...

2 answers  ·  posted 8mo ago by Lundin‭  ·  last activity 8mo ago by matthewsnyder‭

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Q&A How to declare variable-length arrays correctly?

This is meant as a FAQ Q&A regarding variable-length arrays (VLA). The two bugs described below are surprisingly common. I'm trying to use the variable-length arrays feature of C99 (and newe...

1 answer  ·  posted 3y ago by Lundin‭  ·  last activity 9mo ago by Lundin‭

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Q&A Why does calloc accept 2 arguments, and with what arguments should one call it?

According to the standard (C17 draft, 7.22.3.2) The function calloc void *calloc(size_t nmemb, size_t size); "allocates space for an array of nmemb objects, each of whose size is size [and] i...

1 answer  ·  posted 9mo ago by Lover of Structure‭  ·  last activity 9mo ago by Lundin‭

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Q&A What is C23 and why should I care?

The C language has gone through many iterations and the latest one not yet released is informally called "C23", supposedly because they hoped to release it in 2023. The latest draft version N3096 i...

1 answer  ·  posted 9mo ago by Lundin‭  ·  last activity 9mo ago by Lundin‭

Question c c23
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Q&A How to properly use malloc?

I have seen this construct quite a lot: int *p = (int*) malloc(n * sizeof(int)); Is this how it should be? What is the proper way to use malloc? I have also seen this: int *p = malloc(n * size...

3 answers  ·  posted 2y ago by klutt‭  ·  last activity 9mo ago by Lundin‭

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Q&A What are disadvantages of static functions (ie functions with internal linkage) in C?

Functions in C have external linkage by default. In other words, the storage class specifier extern is applied to functions by default, with the effect that they are visible to all translation unit...

3 answers  ·  posted 11mo ago by Lover of Structure‭  ·  last activity 10mo ago by Dirk Herrmann‭

Question c linkage
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Q&A constructor in C

#include<stdio.h> struct Book { char title[20]; char author[20]; int pages; }; void init_Book_types(struct Book* aTitle,struct Book* aAuthor,struct Book* aPages){ aTitle->ti...

2 answers  ·  posted 3y ago by deleted user  ·  last activity 11mo ago by __blackjack__‭

Question c constructor
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Q&A Are there references in C?

When reading posts at programming sites such as this one, I frequently encounter people saying things like: "There is no pass-by-reference in C, everything is passed by value." People claiming su...

3 answers  ·  posted 2y ago by Lundin‭  ·  last activity 11mo ago by Alexei‭

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Q&A Storing more bytes than a union member has, but less than the union size, with memcpy(3)

Let's say we have an object, we store it in a union (into some other narrower type, but with memcpy(3), so it's allowed --I guess--), and then read it from the union via it's original type (so no a...

2 answers  ·  posted 12mo ago by alx‭  ·  last activity 11mo ago by Lundin‭

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Q&A What does the static keyword do in C?

What exactly does the static keyword do in C? I have seen it used in several diverse contexts: 1) As a variable outside a function: #include <stdio.h> static int x = 5; int main (void) ...

1 answer  ·  posted 2y ago by Lundin‭  ·  last activity 12mo ago by Lundin‭

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Q&A Can freed pointers undergo lvalue conversion?

char *p, *q; p = malloc(1); free(p); q = p; // lvalue conversion Is the last lvalue conversion (= p;) Undefined Behavior or not? We didn't take the address of the local p. C11::6.3.2.1...

2 answers  ·  posted 1y ago by alx‭  ·  last activity 1y ago by Dirk Herrmann‭

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Q&A memcmp(3) memory containing invalid values

What does it mean that we can use memcmp(3) on invalid values? ISO C allows comparing an invalid value through memcmp(3), because it doesn't read the value, but rather its representation, and "rea...

2 answers  ·  posted 1y ago by alx‭  ·  last activity 1y ago by Lundin‭

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Q&A Is partial allocation of an object Undefined Behavior?

Is it valid to partly allocate an object, as long as you only use the allocated part of it? #include <stdio.h> #include <stdlib.h> struct s { int i[100]; }; int main(void) {...

1 answer  ·  posted 1y ago by alx‭  ·  last activity 1y ago by Lundin‭

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Q&A Strict aliasing rules and function boundaries

Let's analyze this code, assuming an architecture where the alignment of int64_t is the same as that of double: void bar(double *f, int64_t *j) { *(int64_t *)f = *j; } void foo(void) ...

1 answer  ·  posted 1y ago by alx‭  ·  edited 1y ago by Lundin‭

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Code Reviews stpecpy(): Design a better string copy function that truncates

I was directed a few days ago to a post about a string copy function, which IMO improves the commonly known string copy functions, including strlcpy(3BSD), strlcat(3BSD), and strscpy(9). It define...

2 answers  ·  posted 2y ago by alx‭  ·  last activity 1y ago by alx‭

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Q&A How to write a macro that discards the const qualifier, for any type?

How to write a macro that discards the const qualifier, for any type? I hope some combination of typeof and a cast will do, but haven't found the combination. I tried this, without luck: #define...

2 answers  ·  posted 2y ago by alx‭  ·  last activity 1y ago by alx‭

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Q&A C naming convention, module trigrams?

For my company, I'm writing naming conventions for embedded code in C language. Function names must be named in lowerCamelCase() and start with a verb. Global variables are in Maj_started_lowe...

3 answers  ·  posted 1y ago by AdriZ‭  ·  last activity 1y ago by Dirk Herrmann‭

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Q&A Cast uninitialized variable to (void)

Is it undefined behaviour to cast an uninitialized variable to (void)? Example: int main() { int x; (void)x; return 0; }

4 answers  ·  posted 1y ago by Estela‭  ·  last activity 1y ago by Ethan‭

Question c casting
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Q&A How to do private encapsulation in C?

I'm using an object-oriented design for my C project and trying to implement classes with private encapsulation. How do I do this? Some things I've tried that are problematic: Using a struct f...

1 answer  ·  posted 2y ago by Lundin‭  ·  last activity 1y ago by Lundin‭

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Q&A How to efficiently remove every occurrence of one string inside another

I have two strings and want to remove every occurrence of the second string inside the first one starting from the beginning of the first string and as if each occurrence was removed immediately. ...

1 answer  ·  posted 2y ago by dumplings‭  ·  edited 2y ago by __blackjack__‭

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Q&A Assert that some code is not present in the final binary, at compile or link time.

I'd like to assert that some code can be optimized out, and is not present in the final binary object. #define CONSTANT 0 #if (!CONSTANT) [[landmine_A]] #endif static int foo(void); void...

1 answer  ·  posted 2y ago by alx‭  ·  last activity 2y ago by alx‭

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Q&A Regarding the implementation of data structures.

I'm attempting a question to do with data structures, file streams & linked lists. The code isn't complete yet as I am still halfway working on it. I am required to use data structures in the d...

1 answer  ·  posted 2y ago by dumplings‭  ·  edited 2y ago by Alexei‭

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Q&A How can I modify the code above to accept string as user input and use strcmp to compare with the contents of the text file & then delete that line?

I want to enter a string to compare with the text file, and if that word matches, then I want to delete that line containing that string. How can I modify the code below, since the code below take...

1 answer  ·  posted 2y ago by dumplings‭  ·  edited 2y ago by Alexei‭

Question c file-handling
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Q&A Problems with data structures and filestreams.

So I just started learning how to use file-streams in C & decided to attempt a question which is to do with library management in C, however I am currently encountering some problems and feel l...

2 answers  ·  posted 2y ago by dumplings‭  ·  edited 2y ago by Alexei‭

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Q&A Why does fopen return NULL?

#include<stdio.h> #include<stdlib.h> int main (void){ FILE *cfPtr; char name[15]; int ID; if ((cfPtr = fopen("draft.txt","w")) == NULL){ printf("File could n...

2 answers  ·  posted 2y ago by dumplings‭  ·  edited 2y ago by dumplings‭

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Q&A array of arrays vs array of pointers to store array of string literals

Let's consider the following code: const char a[][4] = {"aa", "aaa"}; const char *b[] = {"bb", "bbb"}; const char *const c[] = {"cc", "ccc"}; For shared libraries, both b and c arrays require...

0 answers  ·  posted 2y ago by alx‭  ·  edited 2y ago by alx‭

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Q&A Child process works only once after the parent's two calls to scanf

This program creates a child process and shares two integers (base and height) through the shared memory. The parent process asks four times to insert two integers and wait for the child process t...

1 answer  ·  posted 2y ago by Luca_Impellizzeri‭  ·  last activity 2y ago by Alexei‭

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Q&A Is `-isystem` a POSIX cc option?

Is -isystem/path/to/sys/includes a standard compiler option, or is it a compiler extension implemented by gcc, clang, and maybe other compilers? Can I rely on its availability? I couldn't find th...

1 answer  ·  posted 2y ago by alx‭  ·  last activity 2y ago by deleted user

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Q&A Should I check if pointer parameters are null pointers?

When writing any form of custom function such as this: void func (int* a, int* b) Should I add code to check if a and b are null pointers or not? if(a == NULL) /* error handling */ When po...

4 answers  ·  posted 2y ago by Lundin‭  ·  last activity 2y ago by Dirk Herrmann‭

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Q&A Which functions in the C standard library must always be avoided?

It would seem that the C standard library is a collection of diverse functions that pretty much just ended up in the standard by tradition or "accident", rather than through some careful plan or ra...

1 answer  ·  posted 2y ago by Lundin‭  ·  last activity 2y ago by Lundin‭

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Q&A What does a variable followed by parentheses ("ptr()") mean?

What does ptr() mean in this code? #include<stdio.h> #include<stdlib.h> void PrintHello() { printf("Hello\n"); } int Add(int a, int b) { return a+b; } int main...

2 answers  ·  posted 2y ago by dumplings‭  ·  last activity 2y ago by Martin Bonner‭

Question c pointers
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Q&A noreturn function with non-void return type

Is it legal ISO C to declare a function as noreturn with a non-void return type (but of course not actually returning)? As far as I can read from the standard, it seems legal. Example: noreturn ...

1 answer  ·  posted 2y ago by alx‭  ·  edited 2y ago by alx‭

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Q&A Is it OK to use scanf with a void pointer?

I've created a function that calls scanf passing a void pointer as argument: void read(const char *format, void *p) { scanf(format, p); } And tested it with different types: int n; read...

2 answers  ·  posted 2y ago by hkotsubo‭  ·  last activity 2y ago by Lundin‭

Question c pointers scanf
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Q&A When does it not work to dereference the pointer for sizeof during malloc?

Background This is kind of a subquestion to How to properly use malloc? When allocating, there are basically two common ways of using the sizeof operator: int *p; p = malloc(n * sizeof *p); /...

1 answer  ·  posted 2y ago by klutt‭  ·  edited 2y ago by hkotsubo‭

Question c pointers malloc
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Q&A Are static pointers implicitly initialized to NULL?

Consider this code: #include <stdio.h> int main(void) { static void *ptr; if(ptr == NULL) puts("It's NULL!"); } I wonder if this is guaranteed to print "It's NULL!" I know ...

1 answer  ·  posted 2y ago by klutt‭  ·  last activity 2y ago by Lundin‭

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Q&A C Language Standard Linking Specifications

What (if anything) does the C standard have to say about linking objects? My guess is that, because C only defines language->behavior rules, it completely ignores any potential intermediate form...

1 answer  ·  posted 2y ago by Josh Hyatt‭  ·  edited 2y ago by Josh Hyatt‭

Question c standard
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Q&A Question regarding an error message in my compiler to do with my code on linked list.

Can anyone help me, I'm currently learning pointers, this is the code I wrote to try and insert a node at the beginning of the list. However at the part where I included the comment of "error at th...

1 answer  ·  posted 2y ago by hamburgersarecool‭  ·  edited 2y ago by hamburgersarecool‭

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Q&A What is malloc's standard-defined behavior with respect to the amount of memory it allocates?

I recently told a friend that malloc(n) allocates and returns a pointer to a block of at least N bytes of memory, as opposed to exactly N; that it is allowed to allocate 'extra' memory to meet e.g....

2 answers  ·  posted 2y ago by ajv‭  ·  last activity 2y ago by bta‭

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Q&A Behavior of Pointer Arithmetic on the Stack

Consider the following code: #include <stdio.h> int main() { int a = 5; int b; ++*(&b + 1); printf("%d\n", a); return 0; } The output is as expected: 6 ...

4 answers  ·  posted 2y ago by Josh Hyatt‭  ·  last activity 2y ago by Alexei‭