C++ 文件打开

Question

我是 C++ 的新手，我想练习打开文件和输入文本，现在我意识到这将是存储登录信息的最糟糕的方式，但这正是我选择模拟它的方式至少它不会完全随机。现在我在所有方面都做得很好，除了一个地方似乎我一直在出错，整个代码是

#include <iostream>
#include <string>
#include <fstream>
#include <new>
using namespace std;
string login() {
    string username, password;
    cout << "What is your username?\n";
    cin >> username;
    cout << "What is your password, " << username << endl;
    cin >> password;
    //Verify info
    return username;
}
string signup() {
    string username, password, cpass, bio;
    do {
        cout << "What is your username?\n";
        cin >> username;
        cout << "What is your password?\n";
        cin >> password;
        cout << "Confirm password: ";
        cin >> cpass;
        cout << "Describe what you like to do:\n";
        cin >> bio;
    } while (password != cpass);
    ofstream user = new ofstream();
    user("users.txt");
    if (user.is_open()) {
        //Make sure the program is writing to the end of the file!
        user.seekp(0,std::ios::end);
        user << username << endl;
        user << password << endl;
        user << bio << endl;
    } else {
        cout << "Something went wrong with opening the file!";
    }
    user.close();
    return username;
}
int main() {
    string answ;
    cout << "Hello, welcome to wewillscamyou.net, are you already signed up?\n";
    if(answ == "Yes" || answ == "yes") {
        string username = login();
    } else {
        string username = signup();
    }
    return 0;
}

但我在这两行遇到错误，这不是因为打字错误，我需要帮助，因为这在 java:

中有效

ofstream user = new ofstream();
user("users.txt");

Answer 1

将文件名传递给 ofstream 构造函数。此外，指定您要附加到文件 - 无需手动查找。

ofstream user("users.txt", ofstream::app);
if (user)
{
    user << username << endl;
    user << password << endl;
    user << bio << endl;
}
else
{
    cout << "Something went wrong with opening the file!";
}

Answer 2

'ofstream'用于写入文本或二进制文件。而 'new' 用于分配内存。要写入文件末尾，您需要先在 'append'(app) 中打开它 mode.It 一旦连接到文件，将自动使用存储驱动器中的内存。

**user.seekp(0,std::ios::end);**

这行代码没有错，但不是必须的

替换这个

ofstream user = new ofstream();
user("users.txt");
if (user.is_open()) {
    //Make sure the program is writing to the end of the file!
    user.seekp(0,std::ios::end);

    user << username << endl;
    user << password << endl;
    user << bio << endl;
}

通过这个:-

ofstream user("user.txt",ios::app);
if(user)
{
    user << username << endl;
    user << password << endl;
    user << bio << endl;
}

Answer 3

C++ 中的 Buddy new 用于创建 动态分配的 对象，或者您有指针指向的对象，或者您必须为其分配内存的对象。通常是指向对象的指针。

class A {
    public:
        A() { }
};

int main () {
    A a (); // object (created as value)
    A *a = new A(); // notice pointer, I need to allocate memory for it thus I have to use `new`
}

结论new在C++中意味着为这个对象分配足够的内存并给我它的地址。因此，要解决您的错误，您有多种选择：

ofstream user ("user.txt");

或

ofstream user;
user = ofstream("users.txt");

或

ofstream user;
user.open("user.txt");
...
user.close("user.txt");
user("users.txt");

C++ 文件打开

file opening in C++

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fstream