qt之输出日志到文件中
描述
助手中在C++ API changes中提到：Qt::qDebug()、Qt::qWarning()、Qt::qCritical()、Qt::qFatal()被改变为宏来跟踪源代码的消息来源。被打印的信息可以被配置（用于缺省消息处理程序），通过设置该新的环境变量QT_MESSAGE_PATTERN。Qt::qInstallMsgHandler()已过时，因此建议使用Qt::qInstallMessageHandler()来代替。
级别
qDebug：调试信息
qWarning：警告信息
qCritical：严重错误
qFatal：致命错误
需求（目的）：生成log.txt日志文件，记录详细日志信息（包括等级、所在文件、所在行号、描述信息、产生时间等）,以便于快速跟踪、定位。
下述代码
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 ddd");
QString current_date = QString("(%1)").arg(current_date_time);
QString message = QString("%1 %2 %3 %4").arg(text).arg(context_info).arg(current_date).arg(msg);
QFile file("log.txt");
file.open(QIODevice::WriteOnly | QIODevice::Append);
QTextStream text_stream(&file);
text_stream << message << "\r\n";
file.flush();
file.close();
mutex.unlock();
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QtGuiApplication1 w;
w.show();
qInstallMessageHandler(outputMessage);
string ss = "nihao";
int a = 18;
qDebug("This is a debug message");
qDebug() << ss.c_str() << a << endl;
qWarning("This is a warning message");
qCritical("This is a critical message");
//qFatal("This is a fatal message");
return a.exec();
}
输出结果：
Debug: File:(QtGuiApplication1.cpp) Line:(72) (2017-08-28 15:59:41 周一) This is a debug message
Debug: File:(QtGuiApplication1.cpp) Line:(73) (2017-08-28 15:59:41 周一) nihao 18
Warning: File:(QtGuiApplication1.cpp) Line:(74) (2017-08-28 15:59:41 周一) This is a warning message
Critical: File:(QtGuiApplication1.cpp) Line:(75) (2017-08-28 15:59:41 周一) This is a critical message
Warning: File:(kernel\qobject.cpp) Line:(246) (2017-08-28 15:59:42 周一) QObject::~QObject: Timers cannot be stopped from another thread