func1.h

#ifndef _FUNC1_H_
#define _FUNC1_H_
void func1print();
#endif

func1.c

#include<stdio.h>
#include "func1.h"

void func1print(){
    printf("This is func1 print!\n");
}

func2.h

#ifndef _FUNC2_H_
#define _FUNC2_H_

void func2print();
#endif

func2.c

#include<stdio.h>
#include "func1.h"
#include "func2.h"

void func2print(){
    printf("In func2, first, call func1:");
    func1print();

    printf("This is func2 print!\n");
}

main.c

#include "func1.h"
#include "func2.h"

int main(){
    func1print();
    func2print();
    return 0;

}

makefile

#Makefile
.PHONY:clean
myapp:	main.o func1.o func2.o
	gcc -o myapp main.o func1.o func2.o
main.o:	main.c func1.h func2.h
	gcc -c main.c
func1.o:func1.c func1.h
	gcc -c func1.c
func2.o:func2.c func1.h func2.h
	gcc -c func2.c
clean:
	$(RM) *.o myapp

執行

>make
gcc -c main.c
gcc -c func1.c
gcc -c func2.c
gcc -o myapp main.o func1.o func2.o

驗證

>./myapp 
This is func1 print!
In func2, first, call func1:This is func1 print!
This is func2 print!

解除make

>make clean
rm -f *.o myapp