No source available error in accessing shared library - c++

Question

I have two project in my Eclipse IDE. My OS is Ubuntu. One is application project and another one is shared lib project. I have linked all paths and libs requirement as discussed in the link. But when I debug, I got error as No source available for "0x0". The error happened at iOCR* pOCR = (iOCR*)create(); when I access the shared library object. What is wrong with my linking?
My shared library codes and application codes are attached.
Shared library header file
#ifndef OCR_DLL_H_
#define OCR_DLL_H_
#include <opencv/cv.h>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <tesseract/baseapi.h>
#include <iostream>
#include "Define.h"
using namespace cv;
namespace VIDEOANALYTICS_PLATFORM {
class iOCR{
public:
virtual ~iOCR(){}
virtual int preProcessing(Mat &img) = 0;
virtual int textExtraction(Mat &img) = 0;
};
class OCR : public iOCR{
public:
OCR(){}
~OCR(){ ; }
int preProcessing(Mat &img);
int textExtraction(Mat &img);
private:
};
}
#endif /* OCR_DLL_H_ */
Shared library cpp
#include "OCR_dll.h"
namespace VIDEOANALYTICS_PLATFORM {
extern "C" iOCR* create_object(){
iOCR *p = new OCR();
return p;
}
extern "C" void destroy_object( iOCR* object )
{
delete object;
}
int OCR::preProcessing(Mat &img){
return SUCCESS;
}
int OCR::textExtraction(Mat &img){
return SUCCESS;
}
}
Application main.cpp
#include <stdio.h>
#include "OCR_dll.h"
#define SUCCESS 0
#define FILE_ERROR 1
#define HTTP_ERROR 2
#define THREAD_ERROR 3
using namespace VIDEOANALYTICS_PLATFORM;
using namespace cv;
void *readImage(void *ptr);
void *postHTTP(void *ptr);
int main(int argc, char *argv[])
{
// on Linux, use "./myclass.so"
void* handle = dlopen("OCR.so", RTLD_LAZY);
iOCR* (*create)();
void (*destroy)(iOCR*);
create = (iOCR* (*)())dlsym(handle, "create_object");
destroy = (void (*)(iOCR*))dlsym(handle, "destroy_object");
iOCR* pOCR = (iOCR*)create();
if(pOCR){
destroy( pOCR );
}//if(pOCR)
dlclose(handle);
return 0;
}
I checked with objdumb and the output is as follow
cdc#cdc-desktop:~/workspace/OCR/Debug$ objdump -TC libOCR.so
libOCR.so: file format elf32-i386
DYNAMIC SYMBOL TABLE:
00000000 DF *UND* 00000000 GLIBC_2.1.3 __cxa_atexit
00000000 w D *UND* 00000000 __gmon_start__
00000000 w D *UND* 00000000 _Jv_RegisterClasses
00000000 DF *UND* 00000000 GLIBCXX_3.4 operator delete(void*)
00000000 DF *UND* 00000000 GLIBCXX_3.4 std::ios_base::Init::Init()
00000000 DF *UND* 00000000 GLIBCXX_3.4 std::ios_base::Init::~Init()
00000000 w D *UND* 00000000 _ITM_deregisterTMCloneTable
00000000 w D *UND* 00000000 _ITM_registerTMCloneTable
00000000 DO *UND* 00000000 CXXABI_1.3 vtable for __cxxabiv1::__class_type_info
00000000 DF *UND* 00000000 CXXABI_1.3 __cxa_pure_virtual
00000000 DF *UND* 00000000 GLIBCXX_3.4 operator new(unsigned int)
00000000 DO *UND* 00000000 CXXABI_1.3 vtable for __cxxabiv1::__si_class_type_info
00000000 w DF *UND* 00000000 GLIBC_2.1.3 __cxa_finalize
00000c95 g DF .text 00000020 Base destroy_object
00000dc4 w DF .text 0000001e Base VIDEOANALYTICS_PLATFORM::OCR::~OCR()
00000de4 g DF .fini 00000000 Base _fini
00000d94 w DF .text 00000030 Base VIDEOANALYTICS_PLATFORM::OCR::~OCR()
00000d94 w DF .text 00000030 Base VIDEOANALYTICS_PLATFORM::OCR::~OCR()
00000d4c w DF .text 0000001e Base VIDEOANALYTICS_PLATFORM::iOCR::~iOCR()
00000cc0 g DF .text 0000000a Base VIDEOANALYTICS_PLATFORM::OCR::textExtraction(cv::Mat&)
00000d78 w DF .text 0000001c Base VIDEOANALYTICS_PLATFORM::OCR::OCR()
00000aec g DF .init 00000000 Base _init
00000e40 w DO .rodata 00000020 Base typeinfo name for VIDEOANALYTICS_PLATFORM::OCR
00000d78 w DF .text 0000001c Base VIDEOANALYTICS_PLATFORM::OCR::OCR()
00003018 g D .bss 00000000 Base __bss_start
00000d26 w DF .text 00000025 Base VIDEOANALYTICS_PLATFORM::iOCR::~iOCR()
00000d6a w DF .text 0000000e Base VIDEOANALYTICS_PLATFORM::iOCR::iOCR()
00000d26 w DF .text 00000025 Base VIDEOANALYTICS_PLATFORM::iOCR::~iOCR()
0000301c g D .bss 00000000 Base _end
00000e18 w DO .rodata 00000018 Base vtable for VIDEOANALYTICS_PLATFORM::iOCR
00000e30 w DO .rodata 0000000c Base typeinfo for VIDEOANALYTICS_PLATFORM::OCR
00000d6a w DF .text 0000000e Base VIDEOANALYTICS_PLATFORM::iOCR::iOCR()
00000cb6 g DF .text 0000000a Base VIDEOANALYTICS_PLATFORM::OCR::preProcessing(cv::Mat&)
00000e00 w DO .rodata 00000018 Base vtable for VIDEOANALYTICS_PLATFORM::OCR
00003018 g D .data 00000000 Base _edata
00000e84 w DO .rodata 00000008 Base typeinfo for VIDEOANALYTICS_PLATFORM::iOCR
00000c6c g DF .text 00000029 Base create_object
00000e60 w DO .rodata 00000021 Base typeinfo name for VIDEOANALYTICS_PLATFORM::iOCR

Answer 1

There are two possible problems that I see.
The first is, and for this I'm only guessing, that you put the shared object in the same path as the executable loading the shared object, and thought that dlopen would look in the process current directory. The manual page says that
If filename contains a slash ("/"), then it is interpreted as a (relative or absolute) pathname. Otherwise, the dynamic linker searches for the library as follows...
And then it lists where the function will look for the shared object, which includes e.g. /usr/lib.
If the library is not in the path that dlopen looks in, then the shared object will not be found.
The simple solution to this first problem is to use an absolute or relative path instead, e.g.
dlopen("./OCR.so", RTLD_LAZY);
This will look in the process current directory (which might not be the same directory as where the executable program is).
The second problem is that you named the shared object libOCR.so, and you ask dlopen to look for OCR.so. The dlopen does not automatically add the lib prefix when looking for files, you need to provide the actual file-name of the shared object.