linux下如下编译:
yang@yang-X230:~/work4c/jpg2bmp-mem$ gcc -c rgbgray2bmpgray.c -o rgbgraybmpgray.o
yang@yang-X230:~/work4c/jpg2bmp-mem$ gcc -c jpeg2rgb.c -o jpeg2rgb.o
yang@yang-X230:~/work4c/jpg2bmp-mem$ gcc -c v4l2main-bmp.c -o v4l2main.o
yang@yang-X230:~/work4c/jpg2bmp-mem$ gcc v4l2main.o jpeg2rgb.o rgbgraybmpgray.o -o v4l2main -ljpeg -L /usr/lib/x86_64-linux-gnu/