第 14 章 结构和其他数据形式（把结构内容保存到文件中）

  1 /*-----------------------------------------
  2     booksave.c -- 在文件中保存结构中的内容
  3 -----------------------------------------*/
  4 
  5 #include <stdio.h>
  6 #include <stdlib.h>
  7 #include <string.h>
  8 
  9 #define MAXTITL 40
 10 #define MAXAUTL 40
 11 #define MAXBKS    10        //最大书籍数量
 12 
 13 char* s_gets(char *st, int n);
 14 
 15 struct book
 16 {
 17     char title[MAXTITL];
 18     char author[MAXAUTL];
 19     float value;
 20 };
 21 
 22 int main()
 23 {
 24     struct book library[MAXBKS];
 25     int index, filecount;
 26     FILE *pbooks;
 27 
 28     if ((pbooks = fopen("book.dat", "a+b")) == NULL)
 29     {
 30         fputs("Can't open book.dat file\n", stderr);
 31         exit(EXIT_FAILURE);
 32     }
 33 
 34     rewind(pbooks);        //定位到文件开始
 35 
 36     int count = 0, size = sizeof(struct book);
 37 
 38     while (count != MAXBKS && fread(&library[count], size, 1, pbooks) == 1)
 39     {
 40         if (count == 0)
 41             puts("Current contents of book.dat:");
 42         
 43         printf("%s by %s: $%.2f\n"
 44             , library[count].title, library[count].author, library[count].value);
 45         
 46         ++count;
 47     }
 48 
 49     filecount = count;
 50 
 51     if (count == MAXBKS)
 52     {
 53         fputs("The book.dat file is full.", stderr);
 54         exit(2);
 55     }
 56 
 57     puts("Please add new book titles.");
 58     puts("Press [enter] at the start of a line to stop.");
 59 
 60     while (count != MAXBKS && s_gets(library[count].title, MAXTITL) != NULL
 61         && library[count].title[0] != '\0')
 62     {
 63         puts("Now enter the author.");
 64         
 65         s_gets(library[count].author, MAXAUTL);
 66 
 67         puts("Now enter the value.");
 68 
 69         scanf("%f", &library[count++].value);
 70 
 71         while (fgetc(stdin) != '\n') continue;    //清理输入行
 72 
 73         if (count != MAXBKS)
 74             puts("Enter the next title.");
 75     }
 76 
 77     if (count > 0)
 78     {
 79         puts("Here is the list of your books:");
 80 
 81         for (index = 0; index != count; ++index)
 82             printf("%s by %s: $%.2f\n"
 83             , library[index].title, library[index].author, library[index].value);
 84 
 85         fwrite(&library[filecount], size, count - filecount, pbooks);
 86     }
 87     else
 88         puts("No books? Too bad.\n");
 89 
 90     puts("Bye.\n");
 91     fclose(pbooks);
 92 
 93     return 0;
 94 }
 95 
 96 char* s_gets(char *st, int n)
 97 {
 98     char *ret_val, *find;
 99 
100     if (ret_val = fgets(st, n, stdin))
101     {
102         if (find = strchr(st, '\n'))
103             *find = '\0';
104         else
105             while (fgetc(stdin) != '\n') continue;
106     }
107 
108     return ret_val;
109 }

booksave.c