Compile a C program in Linux using shared library [duplicate]

Question

I am trying to compile a simple C program in Linux with a shared library.

I have all together in the same folder the following files:

mymain.c

 #include "myclib.h"
 int main() {
   func();
   return 0;
}

myclib.h

 void func();

myclib.c

#include <stdio.h>
void func() {

   printf("hello world!!!!!!!!!!!!\n");

} 

Then I followed these steps:

• gcc -c fPIC myclib.c (create memoryaddress independent objectfile)

  which produces: myclib.o

• gcc -shared -fPIC -o libmyclib.so myclib.o (create shared library)

• gcc -c mymain.c (creates an object file out of main.c)

So far so good - then I have the following files ready:

• main.o
• libmyclib.so

So I try to create a program out of this syntax:

gcc -o program -lmyclib -L. mymain.o

(I guess the prefix lib from libmyclib should be replaced with an l?)

But I get the error message from the gc-compiler:

 *mymain.o: In function `main':
 mymain.c:(.text+0xa): undefined reference to `func'
 collect2: error: ld returned 1 exit status*

I have also tested this syntax:

gcc -o program mymain.c -L -lmyclib -Wl,-rpath,.

Then I get the following error:

 /usr/bin/ld: cannot find -lmyclib.so
 collect2: error: ld returned 1 exit status

What am I doing wrong in these two implementations? How do I compile this program to an executable using shared library?

Answer 1

You need to place -l options on the end of linker invocation command line:

gcc -o program -L. mymain.o -lmyclib