Allocate global pointer inside function

Asked Apr 26 '17 at 10:59

Active Apr 26 '17 at 10:59

Viewed 27 times

I am trying to initialize a global pointer inside a function. This is an example that shows the same issue:

#include <stdlib.h>
#include <assert.h>

int* global = NULL;

void alloc(int* p) {
  p = (int*)malloc(sizeof(int));
  *p = 42;
}

int main() {
  alloc(global);
  assert(global);
}

After the call to alloc global is still NULL. It works if I don't pass global to the function but just use it since it's global.

I would rather keep the function call this way to make it more clear. Is there a way to achieve this? Thanks.

Btw. I'm using gcc 6.3.1

asked Apr 26 '17 at 10:59

sv90

`int *alloc() { p = (int*)malloc(sizeof(int)); *p = 42; return p; }` – Jean-François Fabre Apr 26 '17 at 11:01
3

You should read your C text book again. Focus on passing function parameters by value or by reference. You only change a copy of global within your function. – Gerhardh Apr 26 '17 at 11:01
there's a ton of duplicates of that one. – Jean-François Fabre Apr 26 '17 at 11:02
@Gerhardh: Thanks, that solved my problem. – sv90 Apr 26 '17 at 11:07
[Please see this discussion on why not to cast the return value of `malloc()` and family in `C`.](http://stackoverflow.com/q/605845/2173917). – Sourav Ghosh Apr 26 '17 at 11:55
@SouravGhosh: Thanks for the advice – sv90 Apr 27 '17 at 15:30

Allocate global pointer inside function

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