- Create an .so file and run that file, link the .so from the same path to the executable.
Program:
Program file 1 Header file (foo.h):
/* Shared Libraries with GCC on linux
* Check : http://velrajcoding.blogspot.in
*/
#ifndef foo_h__
#define foo_h__
extern void foo(void);
#endif // foo_h__
Program file 2 foo.c:
/* Shared Libraries with GCC on linux
* Check : http://velrajcoding.blogspot.in
*/
#include <stdio.h>
void foo(void)
{
printf("Hello, I am a shared library");
}
Program file 3 Main file (main.h):
/* Shared Libraries with GCC on linux
* Check : http://velrajcoding.blogspot.in
*/
#include <stdio.h>
#include "foo.h"
int main(void)
{
puts("This is a shared library test...");
foo();
return 0;
}
Compile & execute:
Step 1: Compiling with Position Independent Code
[so_crete]$ ls
foo.c foo.h main.c
[so_crete]$
[so_crete]$ gcc -c -Wall -Werror -fpic foo.c
[so_crete]$ ls
foo.c foo.h foo.o main.c
[so_crete]$
Step 2: Creating a shared library from an object file
[so_crete]$ gcc -shared -o libfoo.so foo.o
[so_crete]$ ls
foo.c foo.h foo.o libfoo.so main.c
[so_crete]$
Step 3: Linking with a shared library
[so_crete]$ gcc -Wall -o test main.c -lfoo
/bin/ld: cannot find -lfoo
collect2: error: ld returned 1 exit status
[so_crete]$
Tell GCC where to find the shared library
[so_crete]$ pwd
/users/vkutrala/vel/sample/so_crete
[so_crete]$ gcc -L /users/vkutrala/vel/sample/so_crete -Wall -o test main.c -lfoo
[so_crete]$ ls
foo.c foo.h foo.o libfoo.so main.c test
[so_crete]$
Step 4: Making the library available at runtime
[so_crete]$ ./test
./test: error while loading shared libraries: libfoo.so: cannot open shared object file: No such file or directory
[so_crete]$
Using LD_LIBRARY_PATH
[so_crete]$ echo $LD_LIBRARY_PATH
[so_crete]$ LD_LIBRARY_PATH=/users/vkutrala/vel/sample/so_crete:$LD_LIBRARY_PATH
[so_crete]$ ./test
./test: error while loading shared libraries: libfoo.so: cannot open shared object file: No such file or directory
[so_crete]$
[so_crete]$
[so_crete]$
What happened? Our directory is in LD_LIBRARY_PATH, but we did not export it. In Linux, if you do not export the changes to an environment variable, they will not be inherited by the child processes
[so_crete]$ export LD_LIBRARY_PATH=/users/vkutrala/vel/sample/so_crete:$LD_LIBRARY_PATH
[so_crete]$ ./test
This is a shared library test...
Hello, I am a shared library
[so_crete]$
Reference:
https://www.cprogramming.com/tutorial/shared-libraries-linux-gcc.html
