Conflicting types with char*

Question

I have a small program to test passing char* pointers in and out of functions. When I compile with cc, I get warning and errors saying I have conflicting types even though all my variables are char* . Please enlighten

#include <stdio.h>

main()
{
    char* p = NULL;

    foo1(p);
    foo2();
}

void foo1(char* p1)
{
}

char* foo2(void)
{
    char* p2 = NULL;

    return p2;
}

p.c:11: warning: conflicting types for ‘foo1’
p.c:7: warning: previous implicit declaration of ‘foo1’ was here
p.c:15: error: conflicting types for ‘foo2’
p.c:8: error: previous implicit declaration of ‘foo2’ was here

Answer 1

You need to prototype your functions before the main() function.

example:

void foo1(char *p1);
char* foo2(void);

int main(.......

Or just put the bodies for those functions above the main function.

Answer 2

As ghills said, to fix the error, move the function definitions above main() or put function prototypes there.

The reason for the error is that when the compiler sees:

foo1(p);
foo2();

before it sees either a declaration or definition of foo1() and foo2(), it assumes the return type of those functions is int. In the early days of C, int was considered to be a reasonable default return type (there was no void type in the earliest versions of C). Nowadays, omitting the return type is considered bad practice and compilers complain about it.