与std :: vector一起使用fread时出错

问题描述

第一次执行是成功的，没有任何错误，但是当它创建 Data.bin 时，使用 fread 会出现一些错误.对不起，我不知道该怎么问，所以请看一下程序.我评论了错误的陈述.

First time execution is success without any error but when it creates Data.bin I get some error when I use fread.Sorry I don't know how to ask it so please look at the program.I commented the error making statement.

#include<iostream>
#include<vector>
using namespace std;

typedef struct myStuff
{
    int cdno;
    string content,des;
}MS;

int main()
{
    vector<MS> data;
    int i=0;
    string in;
    FILE *fr=NULL,*fw=NULL;
    fr=fopen("Data.bin","rb");


    //----------------------------------------------------------------------
    if(fr!=NULL)
    {
        do
        {
            data.resize(++i);
        }while( fread(&data[i-1],sizeof(MS),1,fr) ); //ERROR
        fclose(fr);
    }
    else
        data.resize(++i);

    //----------------------------------------------------------------------
    while(1)
    {
        cout<<"Enter x to exit or c to continue updating data: ";
        cin>>in;
        if(in=="x"||in=="X")
        {
            fw=fopen("Data.bin","wb");
            fwrite(&data[i],sizeof(MS),i,fw);
            fclose(fw);
            exit(0);
        }
        else if(in=="c"||in=="C")
        {
            cout<<"Enter CD no: ";
            cin>>data[i-1].cdno;
            cout<<"Enter Contents: ";
            cin>>data[i-1].content;
            cout<<"Enter Description: ";
            cin>>data[i-1].des;
            data.resize(++i);
        }
        else
            cout<<"Try Again..."<<endl;
    }
}

推荐答案

您不应使用 sizeof(string)或sizeof包含字符串的结构，这毫无意义，它只会为您提供类字符串的编译时间(静态)大小.您应该改用 string.size()返回字符串的动态大小.

you shouldn't use sizeof(string) or sizeof a structure that contains a string, that's meaningless, it just gives you the compile time (static) size of the class string. you should instead use string.size() which returns the dynamic size of the string.

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