GCC Linux C - Compile object header not found - c

Question

I've been working on a module in C (under Linux) that requires another module (headers are in other directories).
My problem is that when I compile the code with my Makefile, the gcc compiler tells me that some headers aren't found.
gcc -c render.c
So I include the directories to find the header but here, gcc tries to find the "main" function which does not exist: it is a module...
gcc /opt/vc/include -c render.c
So I would like to know how is it possible to compile a module (output in module.o) that requires other modules?
Here are my files:
render.c:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include "render.h"
int width,height;
int loop,counter;
int initRender(void(*setup)(void),void(*draw)(void),void(*end)(void))
{
init(&width, &height);
loop = -1;
counter = 0;
setup();
while(loop==-1)
{
Start(width, height);
draw();
End();
counter++;
}
end();
finish();
exit(0);
return 0;
}
render.h:
#include "VG/openvg.h"
#include "VG/vgu.h"
#include "fontinfo.h"
#include "shapes.h"
#ifndef RENDER_H_
#define RENDER_H_
extern int width,height;
extern int loop,counter;
int initRender(void(*setup)(void),void(*draw)(void),void(*end)(void));
#endif
Makefile:
INCLUDEFLAGS=-I/opt/vc/include -I/opt/vc/include/interface/vmcs_host/linux -I/opt/vc/include/interface/vcos/pthreads -IopenVG
LIBFLAGS=-L/opt/vc/lib -lGLESv2 -lEGL -lbcm_host -lpthread -ljpeg -LopenVG
NEEDED= openVG/libshapes.o openVG/oglinit.o
all: render
render.o: render.c
gcc -Wall -g $(INCLUDEFLAGS) -c render.c

Answer 1

You probably want
gcc -Wall -g -I/opt/vc/include -c render.c
this will produce a render.o object file.
Please take time to read the documentation about invoking GCC. In particular, check what every option -Wall, -g, -I and -c means. IMHO the first two are very important.
Later, you probably want to link all your object files into an executable, with some external libraries. Perhaps you want something like
gcc -g -Wall -L/opt/vc/lib render.o main.o -lvc -o myprogram
(you really want the -Wall and -g options; IMHO you need to be an expert to dare avoiding them; once you have debugged your program and want to benchmark it, add -O2 for optimizations)
But surely, you want other options.
Notice that order of arguments to gcc matters a lot
Of course, you should learn about GNU make and you need to use it. See this and that examples. You might use make --trace (with recent make) or remake to debug your Makefile (which is not good). You should also run once make -p to understand more the builtin rules of make.
Perhaps you want a library, then read the Program Library HowTo.