c++ fopen is returning a file * with <bad ptr>'s

Question

I copied this code from the libjpeg example and im passing it standard files;

FILE *soureFile;
if ((soureFile = fopen(sourceFilename, "rb")) == NULL)
{
    fprintf(stderr, "can't open %s\n", sourceFilename);
    exit(1);
}

jpeg_stdio_src(&jpegDecompress, soureFile);
jpeg_read_header(&jpegDecompress, true);

It results in a file pointer that contains no information and therefore breaks on the last line with access violations. Any ideas?

EDIT: On Tobias' advice the fopen does appear to open the file ok but the jpeg_read_header is in turn failing with the access violation still.

EDIT: After a little more digging
http://stackoverflow.com/questions/391917/jpeg-support-with-ijg-getting-access-violation

Answer 1

Use strerror or perror to get exact reason:

FILE *soureFile;
if ((soureFile = fopen(sourceFilename, "rb")) == NULL)
{
    perror("fopen failed");
    exit(1);
}

Answer 2

"select isn't broken".

If fopen returned a valid file pointer, and jpeg_read_header can't use it, someone between those two statements has done something bad to it.

The only one in between is the jpg_stdio_src call, which wouldn't fail if all it's preconditions are fulfilled.

Bottom line: see why jpg_stdio_src fails. My guess: it needs to be constructed using the jpeg_create_decompress macro.