C++实现常用的文件操作

①输出到文本文件(txt)

#include<iostream>
#include<fstream>
using namespace std;
int main() {
    ofstream doc("test.txt", ios::app);
          //ios::app如果没有该文件，生成空文件；
          //如果有文件，在文件尾追加
//如果打开失败
    if (doc.fail()) {
        cout << "error" << endl;
        return 1;
    }
    int temp;
        cin>>temp;
        doc<<temp;//输出到文件中
    doc.close();//关闭输出流
    return 0;
}

②从文本文件读入数据

#include<iostream>
#include<fstream>
using namespace std;
int main() {
    ifstream doc("test.txt");
    int t,sum=0;
    if (doc.fail()) {
        cout << "error "<< endl;
    }
    while (doc >> t) {//从文件中读入一个整型数据且不为空
        sum += t;
        cout << t << endl;//输出这个读取到的数值
    }
    cout<<endl<<sum<<endl;
    doc.close();
       return 0;
}

③二进制写文件

#include<iostream>
#include<fstream>
using namespace std;
int main() {
    ofstream doc("bfile1.dat",ios::out | ios::app | ios::binary);
    if (doc.fail()) {//当文件打开失败时
        cout << "error" << endl;
    }
    float t[] = {1.234,4242.212,4242,314.53,890.2};
    int count = 0;
    while (count < 5) {
        doc.write((char *)&(t[count++]), sizeof(float));
    }
    doc.close();
    return 0;
}

④二进制读文件

#include<iostream>
#include<fstream>
using namespace std;
int main() {
    ifstream doc("bfile1.dat", ios::in | ios::binary);
    if (doc.fail()) {
        cout << "error" << endl;
    }
    float t;
    while (doc.read((char *)&t, sizeof(float))) {
        sum += t;
        cout << t << ends;
    }
    cout << endl << sum << endl;
    doc.close();
} 

⑤二进制读写自定义类

#include<iostream>
#include<fstream>
using namespace std;
class employee {
private:
    int num;
    char name[20];  
    int age;
public:
    void  input(int num1, char * name1, int age1) {
        strcpy_s(name, name1);
        num = num1;
        age = age1;
    }
    void show() {
        cout << num << ends<<name<<ends<<age<<endl;
    }
};
int main() {
    employee e1, e2;
    ofstream os("class.dat",ios::app|ios::binary|ios::out);//输出流
    e1.input(12345, (char*)"小明", 19);
    os.write((char*)(&e1) ,sizeof(e1));
    os.close();

    ifstream is("class.dat", ios::binary | ios::in);//输入流
    is.read((char*)(&e2), sizeof(e2));
    e2.show();
    is.close();
}