QT implementation outputs relevant information to log file

Preface

In the development work , When the program is in use , An error occurred , For users , View log information , It is necessary to check the problem preliminarily

Be careful ： I am here windows Writing of environment ,linux The path and command of are somewhat different ,linux Students of the environment cannot directly copy

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6.15 to update ：

You can also see on the Internet by calling qInstallMessageHandler Install message handler , This is the introduction of the message handler in the official document , That is, we can customize qDebug,qInfo When printing what information , Where to print the information . Put the code at the end of the text

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Go straight to the code ：

.h file

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui {
     class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    static int WriteLog(QString errInfo);

private:
    Ui::MainWindow *ui;
};


#endif // MAINWINDOW_H

.cpp file

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QCoreApplication>
#include <QDir>
#include <QProcess>
#include <QDebug>
#include <QDateTime>
#include <QFile>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    
    ui->setupUi(this);
    WriteLog("---success--- The live broadcast function is set successfully ");
    WriteLog("----infos---- Inserting information into the database ......");
    WriteLog("---warning--- No mount information ");
    WriteLog("----error----/etc/lancoo/rec-server.ini file does not exist ");
}

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

// Main code 
int MainWindow::WriteLog(QString info)
{
    
    QString localApplicationDirPath = QCoreApplication::applicationDirPath();		// The directory where the executable program is located 
    QString log_file;

    QString log_dir=localApplicationDirPath+"/log";
    QDir dir(log_dir);
    //cmd You need to use \, Use / Report errors 
    log_dir.replace("/","\\");
    if(!dir.exists())
    {
    
        // Create in the directory where the executable program is located log file 
        system(QString(" mkdir %1").arg(log_dir).toStdString().data());
        qDebug()<<log_dir;
    }

    QDateTime current_date_time =QDateTime::currentDateTime();
    QString date = current_date_time.toString("yyyy-MM-dd");
    // stay c++ in \ To signify an escape ,\\ Is a character \ 
    log_file=log_dir+"\\"+"log_"+date+".txt";

    // Save the contents of the original file , direct write It will cover up the original content 
    QFile file_read(log_file);
    file_read.open(QIODevice::ReadOnly);
    QByteArray file_readAll = file_read.readAll();
    file_read.close();

    // Write information to the file 
    QFile file_write(log_file);
    if(file_write.open(QIODevice::WriteOnly)){
    
        file_write.write(file_readAll.data());
        QString temp_info;
        temp_info+="[";
        temp_info+=current_date_time.toString("yyyy-MM-dd hh:mm:ss");
        temp_info+="] ";
        temp_info+=info;
        temp_info+="\r\n";    // A newline ,linux by \n
        file_write.write(temp_info.toStdString().data());
    }
    file_write.close();
    return 
}

Just look at the main code , It is defined as a static method so that it can be easily called in other classes

log The file is in the directory where the executable program is located

Be careful ：qt Manage compiled files and source files separately , Through shadow construction , Executable files are probably in other directories . If you check here , Then go to the corresponding directory to find the executable program , If this is not checked , Choose the code source file directory to find

In the custom writeLog On the basis of, we customize the message handler ：

Will customize the function myMessageOutput Written in main.cpp in , The installation of message handlers is written in main() In the method , In this way, all classes in the global qDebug Can print the information directly to the log file . Comment out qInstallMessageHandler(myMessageOutput); perhaps qInstallMessageHandler(0) To reply to the message handler

#include "mainwindow.h"

#include <QApplication>
#include <QDateTime>
#include <QDir>
#include <QFile>
#include <QMutex>
#include <QTextStream>
#include <QDebug>

void myMessageOutput(QtMsgType type, const QMessageLogContext &context, const QString &msg)
 {
    
    //  Lock 
        static QMutex mutex;
        mutex.lock();

        QByteArray localMsg = msg.toLocal8Bit();

        QString strMsg("");
        switch(type)
        {
    
        case QtDebugMsg:
            strMsg = QString("----Debug----");
            break;
        case QtInfoMsg:
            strMsg = QString("----Infos----");
            break;
        case QtWarningMsg:
            strMsg = QString("---Warning---");
            break;
        case QtCriticalMsg:
            strMsg = QString("---Critical---");
            break;
        case QtFatalMsg:
            strMsg = QString("----Fatal----");
            break;
        }

        //  Format output information 
        QString strDateTime = QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss");
        QString strMessage = QString("[%1] %5 %6\t-------------File:%2 Line:%3 Function:%4 ")
                .arg(strDateTime).arg(context.file).arg(context.line).arg(context.function).arg(strMsg).arg(localMsg.constData());

        // Get the directory where the executable program is located 
        QString localApplicationDirPath = QCoreApplication::applicationDirPath();
        QString log_file;
        QString log_dir=localApplicationDirPath+"/log";
        QDir dir(log_dir);
        //cmd You need to use \, Use / Report errors 
        log_dir.replace("/","\\");
        if(!dir.exists())
        {
    
            // Create in the directory where the executable program is located log file 
            system(QString(" mkdir %1").arg(log_dir).toStdString().data());
        }

        QDateTime current_date_time =QDateTime::currentDateTime();
        QString date = current_date_time.toString("yyyy-MM-dd");
        // stay c++ in \ To signify an escape ,\\ Is a character "\"
        log_file=log_dir+"\\"+"log_"+date+".txt";

        //  Output information to file （ Reading and writing 、 Additional form ）
        QFile file(log_file);
        file.open(QIODevice::ReadWrite | QIODevice::Append);
        QTextStream stream(&file);
        stream << strMessage << "\r\n";
        file.flush();
        file.close();

        //  Unlock 
        mutex.unlock();
 }

int main(int argc, char *argv[])
{
    
    //  Install message handler 
    qInstallMessageHandler(myMessageOutput);

    QApplication a(argc, argv);
    MainWindow w;
    qDebug("This is a debug message.");
    qInfo("This is a info message.");
    qWarning("This is a warning message.");
    qCritical("This is a critical message.");
    w.show();
    return a.exec();
}

In this way, you can check the error information directly through the log file in the distribution program

Running results ：

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