追加字符串时出错 - 读取位置访问冲突

Question

我正在尝试将数据矩阵构造成字符串以发送到服务器。但是在将数据附加到字符串时出现错误。为什么会这样？

我要发送的数据是位图图像像素。

我的代码：

string getPixelsFromBitmap(Bitmap& bitmap) {
    //Pass up the width and height, as these are useful for accessing pixels in the vector o' vectors.
    int width = bitmap.GetWidth();
    int height = bitmap.GetHeight();

    auto* bitmapData = new Gdiplus::BitmapData;

    //Lock the whole bitmap so we can read pixel data easily.
    Gdiplus::Rect rect(0, 0, width, height);
    bitmap.LockBits(&rect, Gdiplus::ImageLockModeRead, PixelFormat32bppARGB, bitmapData);

    //Get the individual pixels from the locked area.
    auto* pixels = static_cast<unsigned*>(bitmapData->Scan0);

    //Vector of vectors; each vector is a column.
    //std::vector<std::vector<unsigned>> resultPixels(width, std::vector<unsigned>(height));

    //todo fix string 
    string matrix("");

    const int stride = abs(bitmapData->Stride);
    for (int x = 0; x < width; x++) {
        for (int y = 0; y < height; y++) {
            //Get the pixel colour from the pixels array which we got earlier.
            const unsigned pxColor = pixels[y * stride / 4 + x];

            //Get each individual colour component. Bitmap colours are in reverse order.
            const unsigned red = (pxColor & 0xFF0000) >> 16;
            const unsigned green = (pxColor & 0xFF00) >> 8;
            const unsigned blue = pxColor & 0xFF;

            //Combine the values in a more typical RGB format (as opposed to the bitmap way).
            const int rgbValue = RGB(red, green, blue);

            //Assign this RGB value to the pixel location in the vector o' vectors.
            //resultPixels[x][y] = rgbValue;

            matrix += string(rgbValue + ",");
        }
        matrix += string(".");
    }
    //Unlock the bits that we locked before.
    bitmap.UnlockBits(bitmapData);
    return matrix;
}

Answer 1

在此声明中

matrix += string(rgbValue + ",");

参数表达式表示一个指针运算的表达式，向const char *（","）类型的指针表达式添加整数值rgbValue，显然导致访问超出字符串文字 ",".

的内存

你的意思好像是下面这样

matrix += string( std::to_string( rgbValue ) + ",");

追加字符串时出错 - 读取位置访问冲突

Error on append string - Access violation reading location

c++

string

string-literals

pointer-arithmetic