Solved

C; GD; image output not working

Posted on 2009-07-08
5
208 Views
Last Modified: 2012-05-07
I'm using C to develop a dynamic image set with GD, and am having problems with the output of the image.  The source is simple right now so that I can just get the stupid thing working.  The provided code below compiles without error or problem (using gcc -Wall -lgd testimage.c -o testimage).  When I run it from the command line, the output appears as it should (the content type shows up and then the PNG header and then PNG data), but when I load it in a browser, it doesn't work.

Firefox keeps telling me "You have chosen to open 'testimage' which is an 'application/octet-stream'.  If I embed the image in HTML code using an <IMG> tag, I just get the broken image thing.  IE will not display it either.  I must be missing something.

Any ideas why it's not working?

#include <stdio.h>
#include "gd.h"
 
int main(void)
{
  gdImagePtr im;
  int        black;
  int        white;
 
  im    = gdImageCreate(64, 64);
  black = gdImageColorAllocate(im, 0, 0, 0);
  white = gdImageColorAllocate(im, 255, 255, 255);
 
  gdImageRectangle(im, 0, 0, 63, 63, black);
  gdImageLine(im, 0, 0, 63, 63, white);
 
  printf("Content-Type: image/jpeg\n\n");
  gdImagePng(im, stdout);
 
  gdImageDestroy(im);
  return 0;
}

Open in new window

0
Comment
Question by:BaconU
  • 4
5 Comments
 
LVL 53

Expert Comment

by:Infinity08
ID: 24806010
Don't you want to save the image to a file first ? Right now, you're just printing it to stdout, seemingly to try to construct an HTTP response, but that's not really how HTTP responses are constructed.

Try saving it to a file, then try opening the file, and see if that works.
0
 
LVL 53

Expert Comment

by:Infinity08
ID: 24806081
Something like :
#include <stdio.h>
#include "gd.h"
 
int main(void)
{
  gdImagePtr im;
  int        black;
  int        white;
 
  im    = gdImageCreate(64, 64);
  black = gdImageColorAllocate(im, 0, 0, 0);
  white = gdImageColorAllocate(im, 255, 255, 255);
 
  gdImageRectangle(im, 0, 0, 63, 63, black);
  gdImageLine(im, 0, 0, 63, 63, white);
 
  {
    FILE *out = fopen("image.png", "wb");
    gdImagePng(im, out);
    fclose(out);
  }
 
  gdImageDestroy(im);
  return 0;
}

Open in new window

0
 
LVL 53

Accepted Solution

by:
Infinity08 earned 125 total points
ID: 24806205
Maybe you are trying to make this work as CGI ? Is so, something like what you had should do the trick. After renaming the executable with an extension .cgi, you put it on your web server in the appropriate directory, and then browse to the cgi file using your browser.
0
 

Author Closing Comment

by:BaconU
ID: 31601229
I don't want to save it to a file, because yes I am using it as a CGI.  I apparently have Mal's disease aka  a problem of my brain being missing.  I figured out about the time of your second post that it was a web server parse issue, because I didn't include an extension on the executable.  So, the code works perfectly as it should... just not the operator. :)
0
 
LVL 53

Expert Comment

by:Infinity08
ID: 24806304
Heh, that happens to the best of us ;)
0

Featured Post

Gigs: Get Your Project Delivered by an Expert

Select from freelancers specializing in everything from database administration to programming, who have proven themselves as experts in their field. Hire the best, collaborate easily, pay securely and get projects done right.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Summary: This tutorial covers some basics of pointer, pointer arithmetic and function pointer. What is a pointer: A pointer is a variable which holds an address. This address might be address of another variable/address of devices/address of fu…
Many programs have tried to outwit PowerPoint in terms of technology and skill. These programs, however, still lack several characteristics that PowerPoint has possessed from the start. Here's why PowerPoint replacements won't entirely work for desi…
The goal of this video is to provide viewers with basic examples to understand how to create, access, and change arrays in the C programming language.
Illustrator's Shape Builder tool will let you combine shapes visually and interactively. This video shows the Mac version, but the tool works the same way in Windows. To follow along with this video, you can draw your own shapes or download the file…

775 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question