Home/ Questions/Q 9240571
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-18T08:12:43+00:00

I have a C++ shared library ( libtest-lib.so ) that is linked against by

  • 0

I have a C++ shared library ( libtest-lib.so ) that is linked against by 2 Qt Apps – App A and App B on an embedded Linux platform. I want to be able to reference a single shared pointer from libtest-lib.so by both App A and App B.

Libtest-lib.so is tiny –

test-lib_global.h:

#ifndef TESTLIB_GLOBAL_H
#define TESTLIB_GLOBAL_H

#include <QtCore/qglobal.h>

#if defined(TESTLIB_LIBRARY)
#  define TESTLIBSHARED_EXPORT Q_DECL_EXPORT
#else
#  define TESTLIBSHARED_EXPORT Q_DECL_IMPORT
#endif

#endif // TESTLIB_GLOBAL_H

testlib.h:

#ifndef TESTLIB_H
#define TESTLIB_H

#include "test-lib_global.h"

class TESTLIBSHARED_EXPORT TestLib
{
public:
    TestLib();

    // Notice that it is a reference
    TESTLIBSHARED_EXPORT static int& GetSingleInt();

    // Create a global audio buffer
    TESTLIBSHARED_EXPORT static signed short* getGlobalAudioBuffer();

};

#endif // TESTLIB_H

testlib.cpp:

#include "testlib.h"

int& TestLib::GetSingleInt()
{
    // keep the actual value as static to this function
    int min = 5;
    int max = 500;
    static int s_value(min + (rand() % (int)(max - min + 1)));

    // but return a reference so that everybody can use it
    return s_value;
}

// Create a global audio buffer
signed short* TestLib::getGlobalAudioBuffer() {

    // Create a static audio buffer
    static signed short* globalAudioBuffer = (signed short*)malloc( 1000 * sizeof(signed short) );

    return globalAudioBuffer;

}

TestLib::TestLib()
{
}

Both App A and App B do the following in their main:

int me = TestLib::GetSingleInt();
qDebug() << "SHARED INT IS: " << me;

signed short* audioBuffer = TestLib::getGlobalAudioBuffer();
qDebug() << "SHARED AUDIO BUFFER POINTER IS: " << &audioBuffer;

When I deploy libtest-lib.so and then build and deploy App A and App B, I get the following output:

App A:

SHARED INT IS:  108 
SHARED AUDIO BUFFER POINTER IS:  0xbe844ac8

App B:

SHARED INT IS:  108 
SHARED AUDIO BUFFER POINTER IS:  0xbeff0e64

The int is the same, but the pointer address is different. What am I doing wrong? How can I return an identical shared pointer from the library function?

Thanks –

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    That’s not possible per se. Each process has its separate address space. A shared library shares instructions and data, not memory at runtime. You would have to use shared memory and synchronize between processes accordingly. Qt offers QSharedMemory, which provides a platform-independent API to a raw chunk of shared memory with some basic semaphore-based lock/unlock mechanism for synchronization.

    Alternatively, use another IPC mechanism to stream the audio data, e.g. pipes or sockets. That might make synchronization a whole lot easier, depending on the complexity of interaction between the processes.

    • 0