C++ Shared library: Creation and usage

Question

I am trying to build a shared object to later use a function DoSomethingUseful() from the shared object in other projects. It uses external libraries as well as a bunch of headers that I am using across multiple projects.

Using CMake, I created a project MySharedLib with a header file called library.h:

#ifndef MYSHAREDLIB_LIBRARY_H
#define MYSHAREDLIB_LIBRARY_H



#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <cstdio>

// own header files
#include <header1.h>
#include <header2.h>

#define PI 3.14159265

//tesseract
#include <tesseract/baseapi.h>
#include <leptonica/allheaders.h>


//openCV 
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>

//face detection
#include "opencv2/objdetect.hpp"
#include "opencv2/imgproc.hpp"

void DoSomethingUseul(int[] inparray);


#endif

With library.cpp as

#include "library.h"
void DoSomethingUseful(int[] inparray){...}

My CMake file is as such:

cmake_minimum_required(VERSION 3.10)
project(MYSHAREDLIB)

find_package( OpenCV REQUIRED )

set(CMAKE_CXX_STANDARD 11)

set(MY_INCLUDE_DIR ../source/)
set(MY_OPENCV_CASCADES /opencvpath/openCV34/opencv/sources/data/haarcascades/)
include_directories(${MY_INCLUDE_DIR} ${MY_OPENCV_CASCADES} /usr/include)

link_directories(${MY_INCLUDE_DIR})

add_library(MYSHAREDLIB SHARED library.cpp library.h
        ${MY_INCLUDE_DIR}header1.cpp
        ${MY_INCLUDE_DIR}header1.h
        ${MY_INCLUDE_DIR}header2.cpp
        ${MY_INCLUDE_DIR}header2.h
        )

set_target_properties(MYSHAREDLIB PROPERTIES VERSION 3.10)
set_target_properties(MYSHAREDLIB PROPERTIES SOVERSION 1)

target_link_libraries(MYSHAREDLIB lept tesseract ${OpenCV_LIBS})

The *.so file is created sucessfully, i. e. using Clion, no errors are thrown and the file libMySharedLib.so is there.

However, when I want to use the function DoSomethingUseful() in another file DoSomething.cpp:

#include <iostream>
#include "library.h"

using namespace std;

int main()
{

    int[2] myarray; myarray[0]=1; myarray[1] =2;

    DoSomethingUseful(myarray);

    return 0;
}

And

 g++ -g -Wall -o DoSomething DoSomething.cpp -I ../source/ -L. libMYSHAREDLIB.so 

When I execute

./DoSomething

I get:

./DoSomething: error while loading shared libraries: libMYSHAREDLIB.so: cannot open shared object file: No such file or directory

Before, I compiled without -I ../source/ yielding:

In file included from DoSomething.cpp:8:0:
library.h:19:10: fatal error: header1.h: No such file or directory
 #include <header1.h>

I find many threads dealing with this issue in general, and I gathered already a lot of knowledge about shared objects from those issues, also suceeding in getting examples from various tutorials running. However, I do not suceed with my own project.

This is just one of many questions, but I hope I can get help here and maybe also general hints. Thank you a lot for any help.

Answer 1

Assuming Linux (amend question if wrong). When running an executable, shared libraries are loaded from paths listed in /etc/ld.so.conf only. If you want to load from somewhere else (.) , you have to set the LD_LIBRARY_PATH environment variable, e.g. LD_LIBRARY_PATH=. ./DoSomething