Reading IPTC data from a file parsed with libjpeg

libjpeg is a popular library for parsing jpeg files because it is free, fast, and widely available on many platforms. It is easy to combine libiptcdata with code that already uses libjpeg to decompress a jpeg file. The following example shows how to extract IPTC data while a file is being parsed by libjpeg:

IptcData *d;
struct jpeg_decompress_struct cinfo;
struct jpeg_error_mgr jerr;
FILE * infile;
int ps3_pos = 0, ps3_len;
jpeg_saved_marker_ptr marker;

infile = fopen (path, "r");
if (!infile)
	return -1;

/* decompress the jpeg */
cinfo.err = jpeg_std_error (&jerr);
jpeg_create_decompress (&cinfo);
jpeg_stdio_src (&cinfo, infile);
/* be sure to save the APP13 header, which might contain IPTC data */
jpeg_save_markers (&cinfo, JPEG_APP0+13, 0xffff);
jpeg_read_header (&cinfo, TRUE);

/* look for an IPTC header */
marker = cinfo.marker_list;
while (marker) {
	if (marker->marker == JPEG_APP0+13) {
		ps3_pos = iptc_jpeg_ps3_find_iptc (marker->data,
				marker->data_length, &ps3_len);
		if (ps3_pos > 0)
			break;
	}
	marker = marker->next;

}

if (!marker) {
	/* clean up if we don't find IPTC data */
	jpeg_destroy_decompress (&cinfo);
	fclose (infile);
	return 0;
}

/* parse the IPTC data */
d = iptc_data_new_from_data (marker->data + ps3_pos, ps3_len);

/* clean up */
jpeg_destroy_decompress (&cinfo);
fclose (infile);