问在c++中，ios::app、out和trunc之间有什么不同？

EN

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

int main () {

    char data[100];

    // open a file in write mode.
    ofstream outfile;
    outfile.open("afile.dat");

    cout << "Writing to the file" << endl; 
    cout << "Enter your name: ";
    cin.getline(data, 100);

    // write inputted data into the file.
    outfile << data << endl;

    cout << "Enter your age: "; 
    cin >> data; 
    cin.ignore();

    // again write inputted data into the file.
    outfile << data << endl;
    // close the opened file.
    outfile.close();

    // open a file in read mode.
    ifstream infile; 
    infile.open("afile.dat");

    cout << "Reading from the file" << endl; 
    infile >> data;

    // write the data at the screen. 
    cout << data << endl;

    // again read the data from the file and display it. 
    infile >> data; 
    cout << data << endl;

    // close the opened file.
    infile.close();

    return 0;