C++ Cannot call constructor ' ' directly

问题

I'm working on some OpenCV code and developed it in VS 2008 on windows. I'm trying to run the code on Linux with g++ but I get the error "Cannot call constructor 'ImageProcessor::ImageProcessor' directly" for ImageProcessor and all of the other classes I have created. I've attempted to find a way to indirectly call the constructor, but to no avail. Any suggestion would be great. The code compiles and runs fine on Windows.

if (x == 1){
    cout <<"MODE SELECTED: IMAGE TESTING \n";
    ImageProcessor* IP = new ImageProcessor;
    LaneDetector* LD = new LaneDetector;
    LaneInfo* LI1 = new LaneInfo;
    LaneInfo* LI2 = new LaneInfo;
    LaneVector* LV = new LaneVector;
    cvNamedWindow("Window",CV_WINDOW_AUTOSIZE);

    IplImage* temp = 0;
    IplImage* img0 = 0;
    img0 = cvLoadImage(PICTURE_INPUT);
    CvRect r = cvRect(0,((img0->height)/3),img0->width,((img0->height)/3)+20);
    cout <<"IMG0 LOADED \n";

    while(1){
        IP->ImageProcessor::ImageProcessor(img0, r);
        temp = IP->ImageProcessor::get_processed_image();
        LD->LaneDetector::LaneDetector(temp,r);
        LD->LaneDetector::find_edges();
        LI1 = LD->LaneDetector::find_lanes(5);
        LI2 = LD->LaneDetector::find_lanes(25);
        LV->LaneVector::LaneVector(LI1,LI2);
        LV->LaneVector::print_lane_angle_info();

        if( (cvWaitKey(20) & 255) == 27 ) break;
        cvShowImage("Window", temp);
        hold(1);
    }
}

回答1:

This code is terrible.

Why are you qualifying every member function?

And no, you can't call a constructor on an already-created object. Any constructor parameters should be provided when you initialize the object (which your code does with new, which is also not good C++ coding style). If these arguments aren't supposed to be provided until long after construction, change the "constructor" into a normal member function with an appropriate name.

Your code has numerous memory leaks also. It looks like you're writing Java code with C++ syntax. That's not a good thing.

回答2:

This code is pretty weird, reconstructing IP each time through the loop, on top of an existing object?

Not sure the syntax

IP->ImageProcessor::ImageProcessor(img0, r);

was ever valid. Maybe in very old C++. The normal way of doing this is

new (IP) ImageProcessor(img0, r);

Not saying it's a good idea, but I think it'll do the same thing.

来源：https://stackoverflow.com/questions/9253619/c-cannot-call-constructor-directly

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