Posts tagged 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) ...
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...
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...
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...
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...
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) {...
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) ...
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...
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...
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...
Is it undefined behaviour to cast an uninitialized variable to (void)? Example: int main() { int x; (void)x; return 0; }
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...
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. ...
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...
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...
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...
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...
#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...
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...
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...
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...
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...
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...
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...
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...
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 ...
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...
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); /...
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 ...
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...
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...
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...
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....
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 ...
I get the concept of the heap sort algorithm and its like first you have a heap(ordered binary tree) then we have the Max heap which has the highest element value in the array at the top of the tre...
How to clear the contents of a file using C?
Could someone explain this part of the coding for data structures & linked list? I actually got this code from a textbook but no matter how I read the textbook, I still don't get the concept &a...
I would like to delete a book from the collection by a particular title from my library if the user enters 2 as input for my switch statement. How can I do that with my current code? #include<...
Is there any way where I can modify the original server code so that it accepts any port number instead of the predefined one (i.e., port number 8989)? Port number will be entered in the command li...
Question: There is a list of integers in an array (3,2,1,5,6,4), sort this list in both ASCENDING & DESCENDING order. Create a sort function. #include<stdio.h> #include<stdlib.h> ...
Hey, regarding a question on returning pointers as functions, why does my code produce this error & won't print out the sum = 6? #include<stdio.h> #include<stdlib.h> int *A...
Preface: This is a self-answered Q&A meant as a C string handling FAQ. It will ask several question at once which isn't ideal, but they are all closely related and I'd rather not fragment the p...
What exactly must a C compiler do when it finds a compile-time error? The most obvious kind of errors are language syntax errors, but the C standard also speaks of constraints, which are rules tha...
When reading questions about C programming from beginners, I very often see them describing peculiar run-time errors and crashes, segmentation faults and similar. They have spent a lot of time chas...
No, I'm not trying to get the full program written completely in C by you guys. I only need some way to implement the functionalities of each function I found confusing. In this challenge in Code ...
I'm writing a function that counts the number of assignments for a fscanf format string. I studied the documentation in C standard 7.21.6.2 It looks like it works. It passes all test cases I have w...
#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...
Hello folks, can someone resolve this seg fault with me please, i can't find the error where it occur. Thank you. #include <stdlib.h> #include <stdio.h> int ft_ultimate_range(int *...
I'm writing some functions in C that parses a part of a XML file (using libxml), but instead of extracting the content of the XML node that has a specific name, it outputs a string that's not in UT...
Last year, I started working on a language I named SuperCode but then decided BMPL (Builder's Multi-Purpose Language) as the final name. The language would be written using C and up until now, the ...
