qt-日志

Qt提供了qInstallMsgHandler 方法用来定制消息发生后如何来处理。
qInstallMsgHandler 是一个回调函数，主要是由qDebug、qWarnng、qCritical、qFatal这些函数进行触发，
也就是说，qDeubg这些函数处理的消息文本会被qInstallMsgHandler 所指向的回调函数截获，这样就允许用户自己来处理这些消息文本。
例如，你完全可以将这些消息文本输出并保存到相关的日志文件中。请看下面的示例！

qDebug : 调试信息提示
qWarning: 一般的警告提示
qCritical: 严重错误提示
qFatal: 致命错误提示

注意，release版本的日志中QMessageLogContext内容为空，解决方案请参考
在pro文件中添加一个定义：

DEFINES += QT_MESSAGELOGCONTEXT

qDebug() << "hello from worker thread " << thread()->currentThreadId();

qDebug()<<"Value is "<<c;
qInfo()<<"INFO VALUE is";
qCritical()<<"qWarning";
qFatal("fatal error");
qDebug()<<"Value is "<<c;

qt5

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

	QString text;
	switch (type)
	{
	case QtDebugMsg:
		text = QString("Debug:");
		break;

	case QtWarningMsg:
		text = QString("Warning:");
		break;

	case QtCriticalMsg:
		text = QString("Critical:");
		break;

	case QtFatalMsg:
		text = QString("Fatal:");
	}

	QString context_info = QString("File:(%1) Line:(%2)").arg(QString(context.file)).arg(context.line);
	QString current_date_time = QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss:zzz");
	QString message = QString("%1 %2 %3 %4").arg(current_date_time).arg(text).arg(context_info).arg(msg);


	QDir dir;
	QString currentPath = QApplication::applicationFilePath();
	currentPath += "/comHelper.log";
	QFile file(currentPath);
	file.open(QIODevice::WriteOnly | QIODevice::Append);
	QTextStream text_stream(&file);
	text_stream << message << "\r\n";
	file.flush();
	file.close();

	mutex.unlock();
}

qInstallMessageHandler(outputMessage);
qDebug("comHelper started...");

qt4

void outputMessage(QtMsgType type, const char *msg)
{
	static QMutex mutex;
	mutex.lock();

	QString text;
	switch(type)
	{
	case QtDebugMsg:
		text = QString("Debug:");
		break;

	case QtWarningMsg:
		text = QString("Warning:");
		break;

	case QtCriticalMsg:
		text = QString("Critical:");
		break;

	case QtFatalMsg:
		text = QString("Fatal:");
	}

	QString current_date_time = QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss:zzz");
	QString message = QString("%1 %2 %3").arg(current_date_time).arg(text).arg(msg);


	QDir dir;
	QString currentPath = dir.currentPath();
	currentPath += "/remoteCom.log";
	QFile file(currentPath);
	file.open(QIODevice::WriteOnly | QIODevice::Append);
	QTextStream text_stream(&file);
	text_stream << message << "\r\n";
	file.flush();
	file.close();

	mutex.unlock();
}

qInstallMsgHandler(outputMessage);

qDebug("remoteCom started...");

QString strLog = "param=" + param;
qDebug(strLog.toLatin1().data());