tool/extract.c

   1 /*
   2 ** Extract a range of bytes from a file.
   3 **
   4 ** Usage:
   5 **
   6 **    extract FILENAME OFFSET AMOUNT
   7 **
   8 ** The bytes are written to standard output.
   9 */
  10 #include <stdio.h>
  11 #include <stdlib.h>
  12
  13 int main(int argc, char **argv){
  14   FILE *f;
  15   char *zBuf;
  16   int ofst;
  17   int n;
  18   size_t got;
  19
  20   if( argc!=4 ){
  21     fprintf(stderr, "Usage: %s FILENAME OFFSET AMOUNT\n", *argv);
  22     return 1;
  23   }
  24   f = fopen(argv[1], "rb");
  25   if( f==0 ){
  26     fprintf(stderr, "cannot open \"%s\"\n", argv[1]);
  27     return 1;
  28   }
  29   ofst = atoi(argv[2]);
  30   n = atoi(argv[3]);
  31   zBuf = malloc( n );
  32   if( zBuf==0 ){
  33     fprintf(stderr, "out of memory\n");
  34     return 1;
  35   }
  36   fseek(f, ofst, SEEK_SET);
  37   got = fread(zBuf, 1, n, f);
  38   fclose(f);
  39   if( got<n ){
  40     fprintf(stderr, "got only %d of %d bytes\n", got, n);
  41     return 1;
  42   }else{
  43     fwrite(zBuf, 1, n, stdout);
  44   }
  45   return 0;
  46 }