C++如何写一个登陆窗口的代码

下面是一个简单的登陆窗口的代码示例，用到了Qt框架：

// 登陆窗口类的头文件 LoginDialog.h

#ifndef LOGINDIALOG_H
#define LOGINDIALOG_H

#include <QDialog>

namespace Ui {
class LoginDialog;
}

class LoginDialog : public QDialog
{
    Q_OBJECT

public:
    explicit LoginDialog(QWidget *parent = nullptr);
    ~LoginDialog();

signals:
    void loginSuccess();

private slots:
    void on_loginButton_clicked();

private:
    Ui::LoginDialog *ui;
};

#endif // LOGINDIALOG_H

// 登陆窗口类的实现文件 LoginDialog.cpp

#include "LoginDialog.h"
#include "ui_LoginDialog.h"

#include <QMessageBox>

LoginDialog::LoginDialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::LoginDialog)
{
    ui->setupUi(this);
}

LoginDialog::~LoginDialog()
{
    delete ui;
}

void LoginDialog::on_loginButton_clicked()
{
    QString username = ui->usernameLineEdit->text();
    QString password = ui->passwordLineEdit->text();

    if (username == "admin" && password == "123456") {
        emit loginSuccess();
        accept();
    } else {
        QMessageBox::warning(this, tr("Warning"), tr("Invalid username or password!"));
    }
}

// 登陆窗口的界面文件 LoginDialog.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>LoginDialog</class>
 <widget class="QDialog" name="LoginDialog">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>400</width>
    <height>300</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Login</string>
  </property>
  <widget class="QWidget" name="verticalLayoutWidget">
   <property name="geometry">
    <rect>
     <x>50</x>
     <y>50</y>
     <width>301</width>
     <height>201</height>
    </rect>
   </property>
   <layout class="QVBoxLayout" name="verticalLayout">
    <item>
     <widget class="QLabel" name="usernameLabel">
      <property name="text">
       <string>Username:</string>
      </property>
     </widget>
    </item>
    <item>
     <widget class="QLineEdit" name="usernameLineEdit"/>
    </item>
    <item>
     <widget class="QLabel" name="passwordLabel">
      <property name="text">
       <string>Password:</string>
      </property>
     </widget>
    </item>
    <item>
     <widget class="QLineEdit" name="passwordLineEdit"/>
    </item>
    <item>
     <widget class="QPushButton" name="loginButton">
      <property name="text">
       <string>Login</string>
      </property>
     </widget>
    </item>
   </layout>
  </widget>
 </widget>
 <resources/>
 <connections/>
</ui>

使用方法：

#include "LoginDialog.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    LoginDialog loginDialog;
    QObject::connect(&loginDialog, &LoginDialog::loginSuccess, [&]() {
        // 登陆成功后的操作
    });
    loginDialog.exec();

    return a.exec();
}

需要注意的是，这个示例只是一个简单的登陆窗口，实际应用中需要加入更多的安全措施，例如对密码进行加密处理。