CODEWITHSUNDEEP
cfunctioncastingintegervoid
user2662982
user2662982

Reputation: 367

warning: return makes pointer from integer without a cast but returns integer as desired

I'm trying to find out the proper way to return an integer from a void * function call within C.

ie .. 

#include <stdio.h>

void *myfunction() {
 int x = 5;
 return x;
}

int main() {
  printf("%d\n", myfunction());
  return 0;
}

But I keep getting:

warning: return makes pointer from integer without a cast

Is there a cast I need to do to make this work? It seems to return x without problem, the real myfunction returns pointers to structs and character strings as well which all work as expected.

Upvotes: 10

Views: 68626

Answers (4)

Valeriy
Valeriy

Reputation: 1435

I compiled this source with gcc -pedantic:

 #include <stdio.h>

 void *myfunction() {
   size_t x = 5;  
   return (void*)x;
 }

 int main() {
   printf("%d\n", *(int*)myfunction());
   return 0;
 }

There is no warnings

Upvotes: 0

1&#39;&#39;
1&#39;&#39;

Reputation: 27105

Although you'd think the easiest way to do this would be:

void *myfunction() {
  int x = 5;
  return &x; // wrong
}

this is actually undefined behaviour, since x is allocated on the stack, and the stack frame is "rolled up" when the function returns. The silly but correct way is:

void *myfunction() {
  int *x = malloc(sizeof(int));
  *x = 5;
  return x;
}

Please never, ever write code like this, though.

Upvotes: 0

user2663103
user2663103

Reputation: 121

It's not obvious what you're trying to accomplish here, but I'll assume you're trying to do some pointer arithmetic with x, and would like x to be an integer for this arithmetic but a void pointer on return. Without getting into why this does or doesn't make sense, you can eliminate the warning by explicitly casting x to a void pointer.

void *myfunction() {
 int x = 5;
 return (void *)x;
}

This will most likely raise another warning, depending on how your system implements pointers. You may need to use a long instead of an int.

void *myfunction() {
 long x = 5;
 return (void *)x;
}

Upvotes: 9

aaronman
aaronman

Reputation: 18750

A void * is a pointer to anything, you need to return an address. 

void * myfunction() {
  int * x = malloc(sizeof(int));
  *x=5;
  return x;
}

That being said you shouldn't need to return a void * for an int, you should return int * or even better just int

Upvotes: 2

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