Question

In one file I have this:

#include <stdio.h>
#include <stdlib.h>

static struct node* mynode;

struct node*
example(void)
{
    mynode = malloc(sizeof(struct node));
    ...fill up the struct here...
    return mynode;
}

The calling routine is:

#include <stdio.h>
#include <stdlib.h>

int
main(void)
{
    mynode=example();
}

The node itself is defined in a defs.h file I don’t show here.
The warning I get when compiled with gcc is “assignment makes pointer from integer without a cast” in the calling routine.

Changing to mynode=(struct node*)example(); removes that warning. The routine works in any case but I don’t understand why I’m getting the warning.

Answer 1

In the file calling example, the return type of example is not known, so it is assumed to return an int, which you assign to struct node *. Hence the warning.

You should either declare the prototype for example in the calling file (typing in struct node* example(void); before the calling function) or (better) create a header file called, say, example.h, where you type in the prototype and then include the header file in the calling file (that is, typing in #include "example.h" at the top). The header file thus defines the interface of the file whereexample` is located, and the files using the functions can include the header file, thus making sure all the types match, and removing any compiler warnings.