Can't save image by QImage(save function always return 1)

[stereoMatching]

QImage src("../GIL_with_Qt/images_00/lena.jpg"); //can load the image
std::cout<<src.save("C:\lena2.jpg")<<std::endl; //always return 1

QImage src("../GIL_with_Qt/images_00/lena.jpg"); //can load the image
std::cout<<src.save("C:\lena2.jpg")<<std::endl; //always return 1

To copy to clipboard, switch view to plain text mode 

The codes could load the image perfectly, but can't save it anyway.
Besides, I have only load two kinds of format from the QImage.
Format_Indexed8 and Format_RGB32, I tends to transform the format
of the image by "save"(could I?) because some formats of the images are rare.
But it wouldn't work even "save" always return 1.

How could I solve the problem?
Thanks