Question

Im trying to write out an image file that has the following structure:

P5      //magic number
512 512 //dimension of image
255     //max value per pixel
[Image Data.....]

The standard says after max value there should be a whitespace or newline, then the image data. For whatever mysterious reason, the code below >always< adds in 2 characters at the end of the header (A carriage return and line feed). Which shifts every pixel off by 1.

Here’s what I do:

   FILE *outfile; 
   outfile = fopen(filename,"w");
   int i =0, j =0;
   if(outfile==NULL || outfile == 0){
   printf("Output Failed\n");
   return;
   }
   //print header first 
   fprintf(outfile, "P5\r%d %d\r255",width,height);  
   //print out data now, all one line.
   for(i = 0; i<height; i++){
         for(j=0;j<width;j++){
              fprintf(outfile, "%c",pic[j][i]);
         }
   }

   fclose(outfile);
   printf("output to %s complete.\n", filename);          
   return;

Is there a C subtlety that I’m missing here? How do I get it to not print that extra character? I did a few experiments and I’m at a loss. Thanks for your time.

Answer 1

You must be on windows and your output file is opened in text mode.
Change fopen(filename,"w") to fopen(filename,"wb") to open the file in binary mode and the problem should go away.