Questions tagged [c]
C is a general-purpose programming language used for system programming (OS and embedded), libraries, games, and cross-platform. This tag should be used with general questions concerning the C language, as defined in the ISO 9899 standard (the latest version, 9899:2018, unless otherwise specified — also tag version-specific requests with c89, c99, c11, etc.). C is distinct from C++, and it should not be combined with the C++ tag without a specific reason.
44,743
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Should I cast the result of malloc (in C)?
In this question, someone suggested in a comment that I should not cast the result of malloc. i.e., I should do this:
int *sieve = malloc(sizeof(*sieve) * length);
rather than:
int *sieve = (int *) ...
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680
votes
6
answers
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views
Why is “while( !feof(file) )” always wrong?
What is wrong with using feof() to control a read loop? For example:
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char **argv)
{
char *path = "stdin";
FILE ...
- 210k
661
votes
10
answers
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views
Undefined, unspecified and implementation-defined behavior
What is undefined behavior (UB) in C and C++? What about unspecified behavior and implementation-defined behavior? What is the difference between them?
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answers
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Why are these constructs using pre and post-increment undefined behavior?
#include <stdio.h>
int main(void)
{
int i = 0;
i = i++ + ++i;
printf("%d\n", i); // 3
i = 1;
i = (i++);
printf("%d\n", i); // 2 Should be 1, no ?
volatile int u = 0;
u ...
- 9,845
315
votes
13
answers
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views
Why is the gets function so dangerous that it should not be used?
When I try to compile C code that uses the gets() function with GCC, I get this warning:
(.text+0x34): warning: the `gets' function is dangerous and should not be used.
I remember this has ...
- 6,944
135
votes
7
answers
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views
scanf() leaves the newline character in the buffer
I have the following program:
int main(int argc, char *argv[])
{
int a, b;
char c1, c2;
printf("Enter something: ");
scanf("%d", &a); // line 1
printf("...
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495
votes
11
answers
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views
What is array-to-pointer conversion aka. decay?
What is array-to-pointer conversion aka. decay? Is there any relation to array pointers?
- 5,963
1001
votes
11
answers
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views
What is the strict aliasing rule?
When asking about common undefined behavior in C, people sometimes refer to the strict aliasing rule.
What are they talking about?
- 38.8k
398
votes
1
answer
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views
The Definitive C Book Guide and List
This question attempts to collect a community-maintained list of quality books on the c programming language, targeted at various skill levels.
C is a complex programming language that is difficult ...
844
votes
19
answers
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views
What should main() return in C and C++?
What is the correct (most efficient) way to define the main() function in C and C++ — int main() or void main() — and why? And how about the arguments?
If int main() then return 1 or return 0?
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votes
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Why do I get a segmentation fault when writing to a "char *s" initialized with a string literal, but not "char s[]"?
The following code receives seg fault on line 2:
char *str = "string";
str[0] = 'z'; // could be also written as *str = 'z'
printf("%s\n", str);
While this works perfectly well:
char str[] = "...
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358
votes
15
answers
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views
Removing trailing newline character from fgets() input
I am trying to get some data from the user and send it to another function in gcc. The code is something like this.
printf("Enter your Name: ");
if (!(fgets(Name, sizeof Name, stdin) != NULL)) {
...
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867
votes
13
answers
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Why isn't sizeof for a struct equal to the sum of sizeof of each member?
Why does the sizeof operator return a size larger for a structure than the total sizes of the structure's members?
- 25.8k
398
votes
17
answers
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How to find the size of an array (from a pointer pointing to the first element array)?
First off, here is some code:
int main()
{
int days[] = {1,2,3,4,5};
int *ptr = days;
printf("%u\n", sizeof(days));
printf("%u\n", sizeof(ptr));
return 0;
}
Is there a way to ...
- 4,539
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votes
19
answers
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views
How do I use extern to share variables between source files?
I know that global variables in C sometimes have the extern keyword. What is an extern variable? What is the declaration like? What is its scope?
This is related to sharing variables across source ...
shilpa