How to run c program with .so file

Question

I have gone through all the solutions on StackOverflow as well as Ask Ubuntu.

I have a Go program:

package main

import "C"

//export Getint
func Getint() int {
        return  2
}

func main() {}

and I have generated .so file for the same with name t.so and header filet.h`

Now I would like to use this function in my C program.
I have written the code but I don't know how to execute it.

#include <stdio.h>
#include <t.h>
int main()
{
int a;
a=Getint();
printf("number : %d",a);
return 0;
}

When I execute it with

gcc c.c t.so

it generates a.out file

but at the time of running a.out with ./a.out it gives an error:

./a.out
Error while loading shared libraries: t.so: can not open shared object file: no such file or directory exists.

then I tried with:

gcc -c c.c -l t.so

So it generates c.o file and it is not executable.

Solution 1

Most probably your loader cannot find the library. Try to put the path to the directory where the libarry is located to LD_LIBRARY_PATH prior to run your binary.

export LD_LIBRARY_PATH=/path/to/my/library
./a.out

Solution 2

You should use the linker option -rpath, which tells the linker to add information in the executable program where to find runtime libraries like your .so file.

This can be done using the GCC option -Wl which instructs the GCC frontend program to pass an option to the linker:

$ gcc c.c t.so -Wl,-rpath=$(pwd)

This will pass -rpath=$(pwd) to the linker, and $(pwd) causes the shell to call the pwd command to return the current directory.

As long as you don't move the library the program should work.

---

You can use the environment variable LD_LIBRARY_PATH too, but it's not recommended.

Solution 3

.so files are shared object, meaning object that are available to all applications that need them.. that is, shared. Due to this characteristics, they need to be stored in a well known place. Also, they need to be indexed by the dynamic linker.

In linux for instance you typically have a file /etc/ld.so.conf where all directories where shared object are automatically read from are stored

So your options are:

• Put your shared object file in a well known place
• Put your shared object file in a place of your choice and let the dynamic linker know about it: in linux you can modify ld.so.conf and run ldconfig to update ld indexes
• As other suggested write the path of your .so in the env variable LD_LIBRARY_PATH (since dynamic linker reads it before running your application). This must be done at each environment creation
• As other suggested use -rpath when compiling. Note that in this way you cannot move your .so file after the compilation

Personally I prefer installing the .so file in a system library path

Solution 4

You should use LD_LIBRARY_PATH to let the dynamic linker find your shared library in the list. Syntax is similar to PATH a list of directories separted by :.

On OSX this environment variable is called DYLD_LIBRARY_PATH.

View more solutions