VS2017对二进制文件写入和读出是乱麻麻

代码:#include
#include
using namespace std;
struct student
{
int num;
char name[20];
float score;
};
int main()
{
student stud[5] = { 1001,"Li",85,1002,"Fan",97.5,1004,"Wang",54,1006,"Tan",76.5,1010,"Ling",96 };
fstream iofile("stud.dat", ios::in | ios::out | ios::binary);
if (!iofile)
{
cerr << "open error!" << endl;
abort();
}
for (int i = 0; i < 5; i++)
iofile.write((char*)&stud[i], sizeof(stud[i]));
student stud1[5];
for (int i = 0; i < 5; i = i + 2)
{
iofile.seekg(i * sizeof(stud[i]), ios::beg);
iofile.read((char*)&stud[i / 2], sizeof(stud1[0]));
cout << stud1[i / 2].num << " " << stud1[i / 2].name << " " << stud1[i / 2].score << endl;
}
cout << endl;
stud[2].num = 1012;
strcpy_s(stud[2].name, "Wu");
stud[2].score = 60;
iofile.seekg(2 * sizeof(stud[0]), ios::beg);
iofile.write((char*)&stud[2], sizeof(stud[2]));
iofile.seekg(0, ios::beg);
for (int i = 0; i < 5; i++)
{
iofile.read((char*)&stud[i], sizeof(stud1[i]));
cout << stud1[i].num << " " << stud1[i].name << " " << stud1[i].score << endl;
}
iofile.close();
return 0;
}

运行结果:图片说明

1个回答

 // Q704572.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#include<fstream> 
#include<iostream>
using namespace std;
struct student
{
int num;
char name[20];
float score;
};
int main()
{
student stud[5] = { 1001,"Li",85,1002,"Fan",97.5,1004,"Wang",54,1006,"Tan",76.5,1010,"Ling",96 };
fstream iofile("c:\\stud.dat", ios::in | ios::out | ios::binary);
if (!iofile)
{
cerr << "open error!" << endl;
abort();
}
for (int i = 0; i < 5; i++)
iofile.write((char*)&stud[i], sizeof(student));
student stud1[5];
for (int i = 0; i < 5; i++)
{
iofile.seekg(i * sizeof(student), ios::beg);
iofile.read((char*)&stud1[i], sizeof(student));
cout << stud1[i].num << " " << stud1[i].name << " " << stud1[i].score << endl;
}
cout << endl;
stud[2].num = 1012;
strcpy_s(stud[2].name, "Wu");
stud[2].score = 60;
iofile.seekg(2 * sizeof(stud[0]), ios::beg);
iofile.write((char*)&stud[2], sizeof(stud[2]));
iofile.seekg(0, ios::beg);
for (int i = 0; i < 5; i++)
{
iofile.read((char*)&stud[i], sizeof(stud1[i]));
cout << stud1[i].num << " " << stud1[i].name << " " << stud1[i].score << endl;
}
iofile.close();
return 0;
}

图片说明

如果问题得到解决,请点我回答右边的采纳,谢谢


补充下,后面的也不对,你
stud[2].num = 1012;
strcpy_s(stud[2].name, "Wu");
stud[2].score = 60;
iofile.seekg(2 * sizeof(stud[0]), ios::beg);
iofile.write((char*)&stud[2], sizeof(stud[2]));
更新的是stud
但是最后循环输出的是stud1,所以更新了看不到变化。
这个你自己修改下吧。

caozhy
贵阳老马马善福专业维修游泳池堵漏防水工程 回复qq_40522959: 如果问题得到解决,请点我回答右边的采纳
接近 2 年之前 回复
qq_40522959
奋斗中的cc 谢谢
接近 2 年之前 回复
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