books/apue/freadwrite.c

   1 /*
   2  * A fread() and fwrite() example
   3  */
   4
   5 #include <stdio.h>
   6 #include <stdlib.h>
   7 #include <string.h>
   8
   9 #define NAME_MAX 32
  10
  11 struct data {
  12         int id;
  13         int count;
  14         char name[NAME_MAX];
  15 };
  16
  17 static void usage(const char *progname)
  18 {
  19         printf("Usage: %s < -w | -r > < filename >\n", progname);
  20 }
  21
  22 int main(int argc, char *argv[])
  23 {
  24         size_t ret;
  25         FILE *file;
  26         int i;
  27         struct data data;
  28         char *filepath, *progname;
  29
  30         if (argc != 3) {
  31                 fprintf(stderr, "Wrong number of arguments\n");
  32                 usage(argv[0]);
  33                 exit(1);
  34         }
  35
  36         progname = argv[0];
  37         filepath = argv[2];
  38         if (!memcmp(argv[1], "-w", 2)) {
  39                 struct data datav[2];
  40
  41                 /*
  42                  * Write the structures using fwrite()
  43                  */
  44
  45                 file = fopen(filepath, "w+");
  46                 if (!file) {
  47                         perror("fopen()");
  48                         exit(1);
  49                 }
  50
  51                 /* fill datav[] */
  52                 memset(datav, 0, sizeof(data));
  53                 datav[0].id = 0;
  54                 datav[0].count = 42;
  55                 strncpy(datav[0].name, "luiz", NAME_MAX);
  56
  57                 datav[1].id = 1;
  58                 datav[1].count = 666;
  59                 strncpy(datav[1].name, "capitulino", NAME_MAX);
  60
  61                 ret = fwrite((void *) datav, sizeof(struct data),
  62                              2, file);
  63                 if (ret != 2) {
  64                         perror("fwrite()");
  65                         exit(1);
  66                 }
  67
  68                 goto out;
  69         }
  70
  71         /*
  72          * Write the structures using fwrite()
  73          */
  74
  75         file = fopen(filepath, "r");
  76         if (!file) {
  77                 perror("fopen()");
  78                 exit(1);
  79         }
  80
  81         for (i = 0; i < 2; i++) {
  82                 ret = fread((void *) &data, sizeof(data), 1, file);
  83                 if (ret != 1) {
  84                         if (feof(file)) {
  85                                 fprintf(stderr, "finished reading\n");
  86                                 goto out;
  87                         }
  88
  89                         perror("fread()");
  90                         exit(1);
  91                 }
  92
  93                 printf("id = %d\ncount = %d\nname = %s\n\n", data.id,
  94                        data.count, data.name);
  95         }
  96
  97  out:
  98         fclose(file);
  99         return 0;
 100 }