将结构变量写入 c++ 中的文件

Question

I am trying to store a structure variable in a file in visual c++. Here is my code-

#include<iostream>
#include<fstream>

using namespace std;

struct node {
    int key;
};

int main() {
    node n1, n2;
    n1.key = 39;
    ofstream fout("data.txt", ios::out);
    //fout.seekp(0);
    fout.write(reinterpret_cast<char*>(&n1), sizeof(node));
    std::cout << "position of put pointer after write: " << fout.tellp() << '\n';
    //fin.seekg(-1);
    ifstream fin("data.txt", ios::in);
    fin.read(reinterpret_cast<char*>(&n2), sizeof(node));
    std::cout << "Key: " << n2.key;
    return 0;
}

When reading the structure back, the value in the key field is a junk value. Is there something I am doing wrong?

Answer 1

Close fout before you open fin. This works.

#include<iostream>
#include<fstream>

using namespace std;

struct node {
    int key;
};

int main() {
    node n1, n2;
    n1.key = 39;
    ofstream fout("data.txt", ios::out);
    //fout.seekp(0);
    fout.write(reinterpret_cast<char*>(&n1.key), sizeof(node));
    std::cout << "position of put pointer after write: " << fout.tellp() << '\n';
    fout.close();
    //fin.seekg(-1);
    ifstream fin("data.txt", ios::in);
    fin.read(reinterpret_cast<char*>(&n2.key), sizeof(node));
    std::cout << "Key: " << n2.key;
    return 0;
}