首先，你的语法是错误的，正确的应该是
第一个月
但是，参数类型不匹配，所以这不会起作用。您的目的最好由lambda来实现：

connect(ui->horizontalSlider1, &QSlider::valueChanged, 
        // use context ui-lineEdit2, capture "this" by value,
        // match lamba parameters with the signal parameters
        ui->lineEdit2, [this](int value){ 
             // "this" was captured, so it is implicitly used in line below,
             // and format the integer as numeric string any way you need
             ui->lineEdit2->setText(QString::number(value));
});

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首先更新mainwindow.h中的MainWindow类：

private:
    Ui::MainWindow *ui;
    void updateLineEdit(int);

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然后将其用作mainwindow.cpp的内容：

#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(ui->pushButton1, SIGNAL(clicked()), ui->lineEdit1, SLOT(clear()));
    connect(ui->horizontalSlider1, &QSlider::valueChanged, this, &MainWindow::updateLineEdit);
}
void MainWindow::updateLineEdit(int value) {
    this->ui->lineEdit2->setText(QString::number(value));
}
MainWindow::~MainWindow()
{
    delete ui;
}

型