I/O :文件流

首先搞清流的输入输入出

图解：



ifstream: 搞出的是输入文件流对象

ofstream: 搞出的是输出文件流对象

fstream 输入输出文件流

#include <iostream>
#include <fstream>
#include <cstdlib>
#include <cstring>

using namespace std;

struct Student
{
char name[10];
char num[20];
int age;
};

void disp_all(Student *t, int len)
{
cout << "---------------------" << endl;
for(int i=0; i<len; i++)
{
cout << "number: " << (t+i)->num << endl;
cout << "name: " << (t+i)->name << ", age: " << (t+i)->age << endl;
}
}
void disp(Student *t)
{
cout << "number: " << t->num << endl;
cout << "name: " << t->name << ", age: " << t->age << endl;
}

int main()
{
Student stu[5] = {
"Larry", "1221010", 18,
"DaWei", "1221011", 18,
"LiLi", "1221012", 20,
"PaPa", "1221013", 19,
"HuoFu","1221014", 10,
};

//这种方式不会默认的创建文件
fstream iofile("file/save2.dat", ios::in|ios::out|ios::binary);
if(!iofile)
{
cerr<< "open error" << endl;
abort();//与exit（）的作用相同
}

// 作用: 将stu中的5个元素写到磁盘文件中
for(int i=0; i<5; i++)
iofile.write((char *)&stu[i], sizeof(Student));

Student g[5] = {0};

//作用: 将文件中的5个元素读入内存
iofile.seekg(0, ios::beg);//将文件指针指向文件开头
for(int i=0; i<5; i++)
{
iofile.read((char *)&g[i], sizeof(g[i]));
cout << iofile.tellg() << endl;
}

disp_all(g, 5);

strcpy(stu[2].name,"huahua");
strcpy(stu[2].num, "1234" );
stu[2].age = 12;

//将一个stu元素放在文件开头指定个字节处
iofile.seekp(2*sizeof(Student), ios::beg);
iofile.write((char *)&stu[2], sizeof(Student));

iofile.seekg(2*sizeof(Student), ios::beg);
iofile.read((char *)&g[2], sizeof(Student));

disp_all(g, 5);

iofile.close();

return 0;
}

下面这个在重载输入流的时候用过

cin 流出错

if(cin) ….

标准输出流里

cout.unsetf(ios::dex); //关掉10进制

cout.setf(ios::showbase); //在进制前加上大小写字母