Simple C language separate compilation example

foo.c

#include "foo.h"

int fooSum(struct foo* pFoo) {
  return pFoo->a + pFoo->b;
}

foo.h

struct foo {
   int a;
   int b;
};

main.c

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

int main(int argc, char* argv[]) {
  struct foo f;
  f.a = 1;
  f.b = 2;
  int s = fooSum(&f);
}

makefile

CC = gcc
CFLAGS = -g -Wall
TARGET = foo.exe
OFILES = main.o foo.o
LIBS = -lm

all: $(TARGET)

foo.o: foo.c foo.h
main.o: main.c foo.h
foo.exe: $(OFILES)
	$(CC) $(CFLAGS) -o foo.exe $(OFILES) $(LIBS)

clean:
	$(RM) foo.exe *.o

Directions to create an executable

create foo.o

gcc -c foo.c

create main.o

gcc -c main.c

link foo.o and main.o into foo.exe

gcc -o foo.exe main.o foo.o

compile in link as single command:

gcc -o foo.exe main.c foo.c

or use "make" to do this all for you

make