如何在C++中读取.txt文件

Question

我们有一个.txt，里面有这个

PR-ATT-2 Sep 5 2018 Dec 15 2020
LE-GE-3 Oct 15 2019 Jan 20 2021

在我们的代码中，我们尝试将第一行设置为字符串

#include <string>
#include <array>
#include <cstdlib>
#include <fstream>
#include <istream>
#include <iostream>

using namespace std;

int main(int argc, char* argv[]) {
    ifstream projin;
        projin.open(argv[1], ios::in);
        // Making sure the file opened correctly
        if ((projin.is_open()) == false) {
            cout << "There was an error opening the file";
            return 1;
        } else {
            string projectline;
            getline(projin, projectline);
            cout << projectline << " ";
            projin.close();
            return 2;
        }
    return 0;
}

这不会返回任何内容。但是如果代码看起来像这样

#include <string>
#include <array>
#include <cstdlib>
#include <fstream>
#include <istream>
#include <iostream>

using namespace std;

int main(int argc, char* argv[]) {
    ifstream projin;
        projin.open(argv[1], ios::in);
        // Making sure the file opened correctly
        if ((projin.is_open()) == false) {
            cout << "There was an error opening the file";
            return 1;
        } else {
            string projectline;
            getline(projin, projectline);
            cout << "Hello my name is Alejandro, and my favorite word is 
pneumonoultramicroscopicsilicovolcanoconiosis " << projectline << " ";
            projin.close();
            return 2;
        }
    return 0;
}

这返回“您好，我的名字是Alejandro，我最喜欢的词是肺显微镜硅火山柯萨奇病PR-ATT-2 Sep 5 2018 D”。

我们这一生都搞不清楚到底发生了什么。

Answer 1

我们将其更改为while循环，该循环打印该行直到文件末尾，这给出了我们想要的输出。

ifstream projin;
projin.open(argv[1], ios::in);
// Making sure the file opened correctly
if ((projin.is_open()) == false) {
    cout << "There was an error opening the file";
    return 1;
} else {
    string projectline;
    while (getline(projin, projectline)) {
        cout << projectline << endl;
    }
    projin.close();
    return 2;
}