#include<iostream> #include<fstream> using namespace std; class Student { public: int num; char name[20]; }; int main() { fstream iofile("File.txt", ios::in | ios::out | ios::binary); if (!iofile) { cout << "打开失败" << endl; exit(1); } Student st[2] = { {101 ,"Tom"},{102,"Bob"} }, stunew[2]; for (int i = 0; i < 2; i++) { iofile.write((char*)&st[i], sizeof(Student)); } for (int i = 0; i < 2; i++) { iofile.seekg(i * sizeof(st[i]), ios::beg); iofile.read((char*)&stunew[i], sizeof(Student)); } strcpy(stunew[1].name, "Lux"); stunew[1].num = 103; iofile.seekp(sizeof(st[0]), ios::beg); iofile.write((char*)&stunew[1], sizeof(Student)); iofile.seekg(0, ios::beg); for (int i = 0; i < 2; i++) { iofile.read((char*)&stunew[i], sizeof(Student)); cout << "第" << i + 1 << "个同学的信息：" << stunew[i].name << "：" << stunew[i].num << endl; } iofile.close(); }代码为什么运行错误

你的代码运行错误的原因是，你在写入文件时使用了 `ios::binary` 标志，但在读取文件时没有使用该标志。这会导致在 Windows 系统上读取二进制文件时出现问题。

为了解决这个问题，你需要在读取文件时也使用 `ios::binary` 标志，像这样：

iofile.seekg(i * sizeof(st[i]), ios::beg);
iofile.read((char*)&stunew[i], sizeof(Student));

修改后的完整代码如下：

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

class Student {
public:
    int num;
    char name[20];
};

int main() {
    fstream iofile("File.txt", ios::in | ios::out | ios::binary);
    if (!iofile)
    {
        cout << "打开失败" << endl;
        exit(1);
    }

    Student st[2] = { {101 ,"Tom"},{102,"Bob"} }, stunew[2];
    for (int i = 0; i < 2; i++)
    {
        iofile.write((char*)&st[i], sizeof(Student));
    }

    for (int i = 0; i < 2; i++)
    {
        iofile.seekg(i * sizeof(st[i]), ios::beg);
        iofile.read((char*)&stunew[i], sizeof(Student));
    }

    strcpy(stunew[1].name, "Lux");
    stunew[1].num = 103;

    iofile.seekp(sizeof(st[0]), ios::beg);
    iofile.write((char*)&stunew[1], sizeof(Student));

    iofile.seekg(0, ios::beg);
    for (int i = 0; i < 2; i++)
    {
        iofile.read((char*)&stunew[i], sizeof(Student));
        cout << "第" << i + 1 << "个同学的信息：" << stunew[i].name << "：" << stunew[i].num << endl;
    }

    iofile.close();
    return 0;
}