文本的存储....不懂，请教下

[huanhuan30]

打开一个已经存储有 10个 struct book 结构的二进制文件。。。然后可以进行删除和修改..我写了如下程序，就是无法修改，不知道为什么！！

#include "stdafx.h"
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define LEN 10
#define MAXBKS 20

void Delete (struct book *);
void Alter (struct book *);
void EatLine (void);
struct book 
{
	char title[MAXBKS];
	char author[MAXBKS];
	float value;
};
int main (void)
{
	struct book library[10];
	FILE  *pf;
	int  index;
	int  count = 0; // read calc
	int  choose; // n11
	size_t size = sizeof(struct book);
	if ((pf =fopen("xb.txt", "a+b")) == NULL)
	{
		puts("Can't open xb.txt");
		exit(EXIT_FAILURE);
	}
//	rewind(pf);
	while (count < LEN && fread(&library[count], size, 1, pf) == 1)
	{
		printf("%d. %s by %s  $%.2f....\n", count+1, library[count].title, library[count].author, library[count].value);
        count++;
	}
	puts("select a item to alter......");
	puts("1. delete  2.alter");
	while (scanf("%d", &choose) == 1)
	{
		switch (choose)
		{
		case 1:  Delete(library); break;
		case 2:  Alter(library); break;
		default : puts("not 1 or 2 ....");
		}
        puts("Enter others choose....");
	}
	rewind(pf);
	for (index = 0; index < count; index++)
	{
		fwrite(&library, size, 1, pf);
	}
    return 0;
}
void Alter (struct book *pC)
{
	int i;
	puts("Enter the number you want to alter");
	scanf("%d", &i);
	EatLine();
	puts("Enter the new title");
	gets(pC[i-1].title);
    puts("Enter the new author");
	gets(pC[i-1].author);
	puts("Enter the value...");
	scanf("%f", &pC[i-1].value);
	EatLine();
}
void Delete (struct book *pC)
{
	int i;
    puts("Enter the number your want to delete..");
	scanf("%d", &i);
	strcpy(pC[i-1].title, " ");
	strcpy(pC[i-1].author, " ");
	EatLine();
}
void EatLine (void)
{
	while (getchar() != '\n')
	{
		continue;
	}
}

[yutaooo]

pf =fopen("xb.txt", "a+b")

不是"a+b"吧。应该是 "wb+"。

[huanhuan30]

[Quote=引用 1 楼 yutaooo 的回复:]
C/C++ codepf=fopen("xb.txt","a+b")

不是"a+b"吧。应该是 "wb+"。
[/Quote]
我是说已经有一个 含有 10 个struct book 的二进制文本文件....wb+的话就 清空了。。。。

[yutaooo]

a 是 append 呀。追加。

[yutaooo]

要么你打开2次文件，1次"a+b" 另1次"rb+"。

用2个fd支持不同的操作。fd1支持追加记录。fd2支持读和修改写回。

[猫已经找不回了]

就append模式就可以了,append也可以修改文件的.