Creating statically linkable C "packages"

gistfile1.txt

#define PACKAGE_PRIVATE __attribute__((__visibility__("hidden")))
#define PACKAGE_PUBLIC __attribute__((__visibility__("default")))

/* -------- a.c -------- */

static int the_thing = 42;

PACKAGE_PRIVATE int compute_thing(void) {
	return the_thing;
}

/* -------- b.c -------- */

#include <stdio.h>

PACKAGE_PRIVATE print_thing(int x) {
	printf("thing: %d\n", x);
}

/* -------- api.c -------- */

PACKAGE_PUBLIC void do_thing(void) {
	print_thing(compute_thing());
}

/* -------- main.c -------- */

int main(void) {
	do_thing();
	return 0;
}

/* -------- build.sh -------- */

#!/bin/sh

# quit on error
set -e

rm -f *.o
rm -f check

printf 'building and linking package:\n'

gcc $CFLAGS -o a.o -c a.c
gcc $CFLAGS -o b.o -c b.c
gcc $CFLAGS -o api.o -c api.c
ld -r -o package.o a.o b.o api.o
objcopy --localize-hidden package.o

printf '\npackage public (extern) symbols:\n'
nm -g package.o

printf '\nbuilding and running test program:\n'
gcc $CFLAGS -o check main.c package.o && ./check