fwrite -- 将数据写入到文件中

fwrite 函数文档

函数概要：

fwrite 函数用于将指定尺寸的数据写入到指定的文件中。


函数原型：

#include <stdio.h>
...
size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream);

参数解析：
 

返回值：

1. 返回值是实际写入到文件中的元素个数（nmemb）；

2. 如果返回值与 nmemb 参数的值不同，则有错误发生。


演示：

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

struct Date
{
        int year;
        int month;
        int day;
};

struct Book
{
        char name[40];
        char author[40];
        char publisher[40];
        struct Date date;
};

int main(void)
{
        FILE *fp;
        struct Book *book_for_write, *book_for_read;

        // 为结构体分配堆内存空间
        book_for_write = (struct Book *)malloc(sizeof (struct Book));
        book_for_read = (struct Book *)malloc(sizeof (struct Book));

        if (book_for_write == NULL || book_for_read == NULL)
        {
                printf("内存分配失败！\n");
                exit(EXIT_SUCCESS);
        }

        // 填充结构体数据
        strcpy(book_for_write->name, "《带你学C带你飞》");
        strcpy(book_for_write->author, "小甲鱼");
        strcpy(book_for_write->publisher, "清华大学出版社");
        book_for_write->date.year = 2017;
        book_for_write->date.month = 11;
        book_for_write->date.day = 11;

        if ((fp = fopen("file.txt", "w")) == NULL)
        {
                printf("打开文件失败！\n");
                exit(EXIT_SUCCESS);
        }

        // 将整个结构体写入文件中
        fwrite(book_for_write, sizeof(struct Book), 1, fp);

        // 写入完成，关闭保存文件
        fclose(fp);

        // 重新打开文件，检测是否成功写入数据
        if ((fp = fopen("file.txt", "r")) == NULL)
        {
                printf("打开文件失败！\n");
                exit(EXIT_FAILURE);
        }

        // 在文件中读取结构体并打印到屏幕上
        fread(book_for_read, sizeof(struct Book), 1, fp);

        printf("书名：%s\n", book_for_read->name);
        printf("作者：%s\n", book_for_read->author);
        printf("出版社：%s\n", book_for_read->publisher);
        printf("出版日期：%d-%d-%d\n", book_for_read->date.year, book_for_read->date.month, book_for_read->date.day);

        fclose(fp);

        return 0;
}