Question

我已经使用ofstream将字符串写入二进制文件但是当我用fstream读取相同的二进制文件时它出现访问冲突读取位置错误我已经阅读了一些帖子，但我仍然无法解决我的错误

void activity::creAc(){
cout << "Activity ID : " << endl;
cin >> id;
cout << "Activity Title : " << endl;
cin >> title;
cout << "Activity Type : " << endl;
cin >> type;
cout << "Activity Date : " <<  endl;
cin >> acdate;
cout << "Activity Duration : " <<endl;
cin >> duration;
cout << "Activity Fees : " <<  endl;
cin >> fee;

}

void activity::showTask(){
cout << "Activity Title : " << title<<endl;
cout << "Activity Type : " << type << endl;
cout << "Activity Date : " << acdate << endl;
cout << "Activity Duration : " << duration << endl;
cout << "Activity Fees : " << fee << endl;

}

#include <iostream>
#include <string>
#include "user.h"
#include "Teacher.h"
#include "staff.h"
#include "activity.h"
#include <fstream>
#include <istream>
#include <ostream>
using namespace std;

void main(){
    cout << "1.Create" << endl;
    cout << "2.Read" << endl;
    int choicenum;
    cin >> choicenum;
    switch (choicenum){
    case 1: {
                activity obj;
                ofstream fp2;
                fp2.open("activity.dat", ios::binary | ios::app);
                obj.creAc();
                fp2.write((char*)&obj, sizeof(obj));
                fp2.close();
                break;
    }
    case 2:
    {
        activity obj2;
        ifstream fp1;
        fp1.open("activity.dat", ios::binary);
        while (fp1.read((char*)&obj2, sizeof(obj2))){
                obj2.showTask();
        }
        fp1.close();
    }
    default: exit(0);
    };

    system("pause");
}

Answer 1

像许多容器一样，

std::string实际上是一个智能指针的包装器，它指向一些根据需要动态分配的数据。

将其写入文件只会存储文件写入时的地址（加上长度等支持数据）

因此，当您回读该文件时，您将获得来自不同会话/机器/等的指针。然后，您尝试读取指向的位置，它根本不属于您的程序，因此违反了访问权限。

您需要静态分配已知长度的char，而不是需要指针的任何内容。

Answer 2

错误的声明

class activity {
    // data member is std::string.
    typedef std::string value_type;
    value_type id;
    value_type title;
    value_type type;
    value_type acdate;
    value_type duration;
    value_type fee;
public:
    void creAc();
    void showTask();
};

良好声明

class activity {
    // data member is char[64].
    typedef char value_type[64];
    value_type id;
    value_type title;
    value_type type;
    value_type acdate;
    value_type duration;
    value_type fee;
public:
    void creAc();
    void showTask();
};

您应该了解c ++类的内存布局。

c ++访问冲突读取位置fstream读取

2 个答案: