Can't Convert output of Camera to String

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Dear All,

I have a big problem and i should solve it immediately, i want to do an image processing project, i add a camera sensor in gazebo (standalone gazebo 1.8.7 without ROS), and i can't get output of camera in my code, i can get out put of it in shell with gaztopic echo and gztopic view. i get output of others sensor with subscribe to their topics and i do same for camera but i can't get it!!! it's my code, I'm sure that my code is correct, but i don't know how can i convert output of camera to string?!!!!!!!!!

subLCam  = nodeLCam->Subscribe("~/pioneer3at/leftcamera/leftlink/camera/image", `&Manage::parseLCam, this);`

void Manage::parseLCam(ConstImageStampedPtr &_img)
{
    if ( MGDebug )
        qDebug()<<"<<<MG>>> In parseLEFTCam Function.";

    QString msg(_img->ShortDebugString().c_str());

    qDebug()<<msg;
}