How do I remove “incompatible implicit declaration” warning

Question

gcc -o hellomake hellomake.c hellofunc.c -I.

How do I remove the following warnings (on ubuntu 12.04), without putting all the code in one file?

hellofunc.c: In function 'myPrintHelloMake': hellofunc.c:6:3: warning: incompatible implicit declaration of built-in function 'printf' [enabled by default]

The three files are as follows:

hellomake.c

#include<stdio.h>   
int main() 
{   // call a function in another file   myPrintHelloMake();   
return(0); 
}

hellofunc.c

#include<hellomake.h> 

void myPrintHelloMake(void) {

printf("Hello makefiles!\n");

return;
}

hellomake.h /* example include file */

void myPrintHelloMake(void);

Answer 1

Since hellofunc.c calls printf you need to #include <stdio.h> there.

If hellomake.c calls your myPrintHelloMake function, it should #include "hellomake.h"

hellomake.h should also have include guards , eg

#ifndef HELLOMAKE_H_
#define HELLOMAKE_H_

void myPrintHelloMake(void);

#endif

Answer 2

#inclde<stdio.h>应该在公共头文件中，或者hellofunc.c包含在hellofunc.c 。