sparse/sparse.c

   1 /******************************************************************************
   2  * sparse.c
   3  *****************************************************************************/
   4
   5 #define _FILE_OFFSET_BITS 64
   6 #define _GNU_SOURCE
   7
   8 #include <stdio.h>
   9 #include <string.h>
  10 #include <stdlib.h>
  11
  12 #include <getopt.h>
  13
  14 #define THRESHOLD 1023
  15
  16 void help()
  17 {
  18     fputs("sparse: create a sparse file from stdin\n\n", stderr);
  19     fputs("Usage: sparse [-v] [-c threshold] <output_file>\n\n", stderr);
  20 } /* help() */
  21
  22
  23 int main(int argc, char ** argv)
  24 {
  25     int c, i, verbose=0;
  26     long offset=0;
  27     unsigned long threshold = THRESHOLD, seeks=0;
  28     FILE *fo;
  29
  30     while( (c = getopt(argc, argv, "vhc:")) != -1 )
  31     {
  32         switch(c)
  33         {
  34             case 'c':
  35                 /* 0 is acceptable */
  36                 threshold = strtoul(optarg, NULL, 10);
  37                 break;
  38
  39             case 'v':
  40                 verbose = 1;
  41                 break;
  42
  43             case 'h':
  44                 help();
  45                 return 0;
  46
  47             default:
  48                 help();
  49                 return 1;
  50         }
  51     }
  52
  53
  54     if(optind >= argc)
  55     {
  56         help();
  57         return 1;
  58     }
  59
  60     fo = fopen(argv[optind], "w");
  61     if(!fo)
  62     {
  63         perror("fopen() failed");
  64         return 1;
  65     }
  66
  67     while((c = getc(stdin)) != EOF)
  68     {
  69         if(0 == c) offset++;
  70         else
  71         {
  72             if(offset > threshold)
  73             {
  74                 if(verbose) fprintf(stderr, "seek: offset CUR + %ld\n", offset);
  75                 seeks++;
  76                 fseek(fo, offset, SEEK_CUR);
  77                 offset = 0;
  78             }
  79             else if(offset > 0)
  80             {
  81                 for(i=0; i<offset; i++)
  82                     putc(0, fo);
  83                 offset = 0;
  84             }
  85
  86             putc(c, fo);
  87         }
  88     }
  89
  90     if(offset > 0)
  91     {
  92         if(verbose) fprintf(stderr, "seek: offset CUR + %ld\n", offset-1);
  93         seeks++;
  94         fseek(fo, offset-1, SEEK_CUR);
  95         putc(0, fo);
  96     }
  97
  98     fclose(fo);
  99
 100     if(verbose) fprintf(stderr, "total seeks: %lu\n", seeks);
 101
 102     return 0;
 103 } /* main() */
 104