Creating a Shared and Static Library Using Gnu Compiler

Sample steps to create static and shared Library using gcc.

Program for which Library is created

Library Contains code to multiply two integers.

Header file contains Function Declaration.

find_mul.h

int multiply(int, int);

Source file contains Function Definition

find_mul.c

int multiply(int a, int b)
{
return (a * b);
}

Creating Static Library

A static library is a set of object files that were copied into a single file. This single file is the static library. Executable contains static Libraries at compile time itself. The static file is created with the archiver (ar).

we create object file for find_mul.cpp

gcc -c find_mul.c -o find_mul.o

and Static Library is

ar  rcs libmul.a find_mul.o

Note: the library must start with the three letters lib and have the suffix .a

Creating a Shared Library

Shared Libaries need position independent code which is done by -fPIC

gcc -c -fPIC find_mul.c -o find_mul.o

and Shared Library is

gcc -shared -o libmul.so  find_mul.o

Sample Program Using Library

main.c

#include
#include "find_mul.h"
int main()
{
int a = 20;
int b = 30;
printf("Multplication is %d\n", multiply(a, b));
return 0;
}

Linking against static Library

gcc -static main.c -L. -lmul -o statically_linked

For Running

$ ./statically_linked

Linking against static Library

gcc main.c -o dynamically_linked -L. -lmul

For Running,

$ LD_LIBRARY_PATH=.

$ ./dynamically_linked

Thanks to web.


@kova