opencv 将内存中图片读入到mat矩阵

Mat src = imread("1.jpg");
vector<uchar> buff;//buffer for coding 
vector<int> param = vector<int>(2);
param[0] = CV_IMWRITE_JPEG_QUALITY;
param[1] =95;//default(95) 0-100 
imencode(".jpg", src, buff, param);
cout << "coded file size(jpg)" << buff.size() << endl;//fit buff size automatically. 
Mat jpegimage = imdecode(Mat(buff), CV_LOAD_IMAGE_COLOR);

std::ifstream file("1.jpg", std::ios::binary);
std::vector<char> data;
file >> std::noskipws;
std::copy(std::istream_iterator<char>(file), std::istream_iterator<char>(), std::back_inserter(data));
Mat jpegimage = imdecode(Mat(data), CV_LOAD_IMAGE_COLOR);
file.close();