Global variable pass the null value - c++

Question

I'm try to pass string value from mainwindow.cpp to userdetails.cpp. I had been used global variable. When the program run it does not pass the variable value to the userdetails.cpp. When I use qDebug( globelusername.toLatin1() ) it does not show any value. What is the error in this code? globelusername mean, the global variable.
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "register.h"
#include "userdetails.h"
extern QString globelusername;
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
QString globelusername;
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
ui ->loginusername->setPlaceholderText("Username");
ui ->loginpassword->setPlaceholderText("Password");
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_pushButton_2_clicked()
{
//database connection
...........
QString username = ui ->loginusername ->text();
QString password = ui ->loginpassword ->text();
if(db.open()){
//query create
// QMessageBox::information(this, "Sucessfull ","Sucessfully Connect the Database");
QSqlQuery query(QSqlDatabase::database("MyConnect"));
query.prepare(QString("SELECT * FROM user_reg_elec WHERE username = :username AND password = :password"));
query.bindValue(":username", username);
query.bindValue(":password", password);
QString globelusername = username; //globlevariable
}
userdetails.cpp
#include "userdetails.h"
#include "ui_userdetails.h"
#include <QSqlError>
#include "mainwindow.h"
#include <iostream>
Userdetails::Userdetails(QWidget *parent) :
QDialog(parent),
ui(new Ui::Userdetails)
{
ui->setupUi(this);
}
Userdetails::~Userdetails()
{
}
void Userdetails::on_pushButton_4_clicked()
{
{
// database connection
...........
qDebug(globelusername.toLatin1() );

Answer 1

You are not setting globelusername. instead, you are creating a local variable with the following line:
QString globelusername = username; //globlevariable
remove the variable type before setting the value:
globelusername = username; //globlevariable