JPEG support with ijg - getting access violation

Question

I was recently trying to update my game to store graphics in compressed formats (JPEG and PNG).

Whilst I ended up settling on a different library, my initial attempt

Answer 1

I agree with Hernán. This is not a good interface (I think the internal code itself is probably good), unless you really need to work low-level (and maybe not even then). I think ImageMagick is probably better. They have a "MagickWand" C interface that is more high level, not to mention that it supports many more formats.

However, I was curious about libjpeg's interface, so I got a test program working to my satisfaction, based on your example program as well as libjpeg.doc, the IJG example, and USING THE IJG JPEG LIBRARY. Anyway, here's the code. It just prints out the dimensions, and the RGB of the first pixel of every row.

I am very surprised you get an error with my code. It works fine for me, and compiles without any warnings. Can someone else test it?

#include 
#include 
#include 

int main(int argc, char* argv[])
{
    struct jpeg_decompress_struct cinfo;
    struct jpeg_error_mgr jerr;
    JSAMPARRAY buffer;
    int row_stride;

    //initialize error handling
    cinfo.err = jpeg_std_error(&jerr);

    FILE* infile;
    infile = fopen("Sample.jpg", "rb");
    assert(infile != NULL);

    //initialize the decompression
    jpeg_create_decompress(&cinfo);

    //specify the input
    jpeg_stdio_src(&cinfo, infile);

    //read headers
    (void) jpeg_read_header(&cinfo, TRUE);

    jpeg_start_decompress(&cinfo);

    printf("width: %d, height: %d\n", cinfo.output_width, cinfo.output_height);

    row_stride = cinfo.output_width * cinfo.output_components;

    buffer = (*cinfo.mem->alloc_sarray)
        ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);

    JSAMPLE firstRed, firstGreen, firstBlue; // first pixel of each row, recycled
    while (cinfo.output_scanline < cinfo.output_height)
    {
    (void)jpeg_read_scanlines(&cinfo, buffer, 1);
    firstRed = buffer[0][0];
    firstBlue = buffer[0][1];
    firstGreen = buffer[0][2];
    printf("R: %d, G: %d, B: %d\n", firstRed, firstBlue, firstGreen);
    }

    jpeg_finish_decompress(&cinfo);

    return 0;
}