Qt's custom log file, QtMessageHandler application

Table of contents

I. Introduction

After the qt program is released, it is necessary to check some debugging output information. Generally, the output information is written into the log file. This paper uses a custom function to automatically output the Debug, Warning, Critical, Fatal, and Info information to the log file. Just add two lines of code to the main function.

In addition, in order to prevent too much output of the log file and prevent the file from being too large, the function of automatically overwriting and rewriting the file exceeding the maximum limit has been added. For example, if the size of the set log file does not exceed 1M, then the previous content can be cleared after exceeding 1M, and only the The latest 1M.

Two, header file code

lodges.h

#pragma once

#include <QMutex>
#include <QString>

#define LOG_FILE_NAME QString("/Log/") + QDateTime::currentDateTime().toString("yyyy-MM-dd-hh-mm-ss") + QString(".log")
#define MAX_SIZE 1024 * 1024 //文件最大1M

static int s_logLevel = QtDebugMsg;
static QMutex s_logMutex;
static QString s_logPath;

void setLogPath(const QString& path);
void setLogLevel(int level);
void customLogMessageHandler(QtMsgType type, const QMessageLogContext& ctx, const QString& msg);

3. Source file code

lodges.cpp

#include "loger.h"
#include <QFile>
#include <QFileInfo>
#include <QDir>
#include <QTextStream>
#include <QDateTime>


void setLogPath(const QString& path)
{
	s_logPath = path;
}

void setLogLevel(int level)
{
	s_logLevel = level;
}

bool static ensureDirExist(const QString& dirPath)
{
	QDir dir(dirPath);
	if (dir.exists())
	{
		return true;
	}

	return dir.mkpath(dirPath);
}

void customLogMessageHandler(QtMsgType type, const QMessageLogContext& ctx, const QString& msg)
{
	if (type < s_logLevel)
	{
		return;
	}

	QString logInfo;
	QString logTime = QDateTime::currentDateTime().toString("yyyy-MM-dd hh-mm-ss.zzz");
	switch (type)
	{
	case QtDebugMsg:
		logInfo = QString("%1 [Debug] %2").arg(logTime, msg);
		break;

	case QtWarningMsg:
		logInfo = QString("%1 [Warning] %2").arg(logTime, msg);
		break;

	case QtCriticalMsg:
		logInfo = QString("%1 [Critical] %2").arg(logTime, msg);
		break;

	case QtFatalMsg:
		logInfo = QString("%1 [Fatal] %2").arg(logTime, msg);
		abort();
	case QtInfoMsg:
		logInfo = QString("%1 [Info] %2").arg(logTime, msg);
		break;
	}

	s_logMutex.lock();
	QFile outFile(s_logPath);
	QFileInfo fileInfo(outFile);
	if (!ensureDirExist(fileInfo.absoluteDir().absolutePath()))
		return;

	if (outFile.size() > MAX_SIZE)
	{
		if (!outFile.open(QIODevice::WriteOnly | QIODevice::Text))
			return;
	}
	else
	{
		if (!outFile.open(QIODevice::WriteOnly | QIODevice::Append | QIODevice::Text))
			return;
	}

	QTextStream ts(&outFile);
	ts << logInfo.toUtf8() << endl;
	outFile.close();
	s_logMutex.unlock();
}

4. Example of use

#include "loger.h"

int main(int argc, char *argv[])
{
    setLogPath("./" + LOG_FILE_NAME);
    qInstallMessageHandler(customLogMessageHandler);

    //...其他代码.....

}

Just add the above code to the main function, then run the code later, the output content using qDebug, qInfo... will not be output on the console, and all will be in the log file.