第 14 章 结构和其他数据形式（把结构内容保存到文件中）

/*-----------------------------------------
    booksave.c -- 在文件中保存结构中的内容
-----------------------------------------*/

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

#define MAXTITL 40
#define MAXAUTL 40
#define MAXBKS    10        //最大书籍数量

char* s_gets(char *st, int n);

struct book
{
    char title[MAXTITL];
    char author[MAXAUTL];
    float value;
};

int main()
{
    struct book library[MAXBKS];
    int index, filecount;
    FILE *pbooks;

    if ((pbooks = fopen("book.dat", "a+b")) == NULL)
    {
        fputs("Can't open book.dat file
", stderr);
        exit(EXIT_FAILURE);
    }

    rewind(pbooks);        //定位到文件开始

    int count = 0, size = sizeof(struct book);

    while (count != MAXBKS && fread(&library[count], size, 1, pbooks) == 1)
    {
        if (count == 0)
            puts("Current contents of book.dat:");
        
        printf("%s by %s: $%.2f
"
            , library[count].title, library[count].author, library[count].value);
        
        ++count;
    }

    filecount = count;

    if (count == MAXBKS)
    {
        fputs("The book.dat file is full.", stderr);
        exit(2);
    }

    puts("Please add new book titles.");
    puts("Press [enter] at the start of a line to stop.");

    while (count != MAXBKS && s_gets(library[count].title, MAXTITL) != NULL
        && library[count].title[0] != '')
    {
        puts("Now enter the author.");
        
        s_gets(library[count].author, MAXAUTL);

        puts("Now enter the value.");

        scanf("%f", &library[count++].value);

        while (fgetc(stdin) != '
') continue;    //清理输入行

        if (count != MAXBKS)
            puts("Enter the next title.");
    }

    if (count > 0)
    {
        puts("Here is the list of your books:");

        for (index = 0; index != count; ++index)
            printf("%s by %s: $%.2f
"
            , library[index].title, library[index].author, library[index].value);

        fwrite(&library[filecount], size, count - filecount, pbooks);
    }
    else
        puts("No books? Too bad.
");

    puts("Bye.
");
    fclose(pbooks);

    return 0;
}

char* s_gets(char *st, int n)
{
    char *ret_val, *find;

    if (ret_val = fgets(st, n, stdin))
    {
        if (find = strchr(st, '
'))
            *find = '';
        else
            while (fgetc(stdin) != '
') continue;
    }

    return ret_val;
}