文件写入问题，q指针指向内容无变化

Question

从文件随机读入数据1，3，5，写到p指针中，但是p指向内容始终没变

#include <iostream>
#include <fstream>
#include <string>
using namespace std;
struct student
{
    int num;
    string name;
};
int main()
{
    student stu[5] = { 1000,"wang",1001,"ling",1002,"zhang",1003,"zhao",1004,"cheng" };
    fstream file("stu.dat", ios::in | ios::out | ios::binary);
    for (int i = 0; i < 5; i++)
    {
        file.write((char*)&stu[i], sizeof(stu[0]));
    }
    file.seekg(ios::beg);
    void* p;
    p= &stu[0];
    student* q = &stu[1];
    for (int i = 0; i < 5; i=i+2)
    {
        file.seekg( i * sizeof(stu[0]),ios::beg);
        file.read((char*)p, sizeof(stu[0]));
        file.read((char*)&stu[i], sizeof(stu[0]));
        q = (student*)p;
        cout << q->num << '\t' << q->name << endl;
        cout << stu[i].num << '\t' << stu[i].name << endl;
    }
    file.close();
    system("pause");
    return 0;
}

运行结果
1000    wang
1000    wang
1000    wang
1002    zhang
1000    wang
1004    cheng

Answer 1

你检查一下你的文件写成功了吗。。。。检查了半天代码，发现是文件根本就没有成功创建。
第13行后面添加如下代码判断文件是否成功创建：

fstream file("stu.dat", ios::in | ios::out | ios::binary);  //在这一行后面添加如下代码：
    //判断文件是否成功打开
    if (!file.is_open())
    {
        cout << "file cannot open"<<endl;
        system("pause");
        return 0;
    }