Thread: offset

I'm not sure I understand your question, but here goes:

Code:

/* Scan for a matching byte */

    offset = -1;
    x = 1;                  //File offset

    while(fgets(buffer,MAXCHAR,f))
    {
        if( (a = strstr(buffer,text)) != NULL)
        {
            matches++;      //inc. match count
            printf("Found at offset %Lu\n",x+a-buffer);
            offset = x + a - buffer;
    
        }
        x+=strlen(buffer);      //adjust offset
    }
    if (offset != -1)
       printf("last match found at offset: %d\n",offset);
    printf("end of file at offset: %d\n",x);

The best I've been able to string this together, since Rhidian has spread questions and various fragments from replies around various threads and forums, is like this:

Search through a file (likely a JPEG) opened in binary mode and search for this format's end-of-file indicator, which happens to be a hex value such as FFD9.

A quick hack, since I'm not exactly sure that this is what Rhidian is asking, might be something like this.

Code:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
   static const char filename[] = "Ocean Wave.jpg";
   FILE *file = fopen(filename, "rb");
   if ( file != NULL )
   {
      unsigned char *buffer;
      long i, size;

      fseek(file, 0L, SEEK_END);
      size = ftell(file);
      rewind(file);

      buffer = malloc(size);
      if ( buffer != NULL )
      {
         static const unsigned char jpeg_eof[] = {0xFF,0xD9};
         if ( fread(buffer, sizeof *buffer, size, file) == size )
         {
            for ( i = 0; i < size - 1; ++i )
            {
               if ( buffer[i] == jpeg_eof[0] && buffer[i + 1] == jpeg_eof[1] )
               {
                  printf("i = %lX, size = %lX\n", i, size);
                  break;
               }
            }
         }
      }
      free(buffer);
      fclose(file);
   }
   else
   {
      perror(filename);
   }
   return 0;
}

/* my output
i = 121B7, size = 121B9
*/

Judging from the comments in Rhidian's code, that looks like what he's after.