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Qt浅谈之二十一log调试日志

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12/01
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一、简单介绍

近期因调试code时，想了解程序的流程，但苦于没有一个简易的日志记录，不停使用qDebug打印输出，而终于提交代码时得去多次删除信息打印，有时还会出现新改动的代码分不清是哪些部分。而使用#ifdef _DEBUG又比較烦这套，因此写了些简单的日志，方便排除问题，临时不能用于多线程中，以后须要再补充。

二、具体解释

1、追踪函数 
#ifdef _DEBUG_PRINT

#define DEBUGPRINT DEBUGInfo printinfo(__FILE__, __LINE__, __FUNCTION__);

#else

#define DEBUGPRINT

#endif

class DEBUGInfo

{

public:

    DEBUGInfo(QString file, int line, QString func);

    ~DEBUGInfo();

private:

    QString fileName;

    int fileLine;

    QString funcName;

};
DEBUGInfo::DEBUGInfo(QString file, int line, QString func)

    :fileName(file)

    ,fileLine(line)

    ,funcName(func)

{

  QString result = "";

  QString beginTime = QDateTime::currentDateTime().toString("[yyyy-dd-MM hh:mm:ss.zzz] ");

  result += beginTime + "Enter:{" + fileName + ":" + QString::number(fileLine) + "---" + funcName + "}";

  qDebug() << result.toStdString().c_str();

}

DEBUGInfo::~DEBUGInfo()

{

  QString result = "";

  QString beginTime = QDateTime::currentDateTime().toString("[yyyy-dd-MM hh:mm:ss.zzz] ");

  result += beginTime + "Leave:{" + fileName + ":" + QString::number(fileLine) + "---" + funcName + "}";

  qDebug() << result.toStdString().c_str();

}

使用：在须要查看的函数中增加DEBUGPRINT就可以。输出文件名称，所在的行和函数名字。 

void HelloWorld()

{

    DEBUGPRINT

}

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2、信息打印和写日志文件 
enum LOGLEVEL{

    LOG_DEBUG = 0,      /**< Debug >**/

    LOG_INFO,           /**< Info >**/

    LOG_WARN,           /**< Warn >**/

    LOG_ERROR           /**< Error >**/

};

class LogWriter{

    public:

        static LogWriter* getLogCenter();

        void PrintLog(LOGLEVEL level, const char* msg, ...);

        void SaveFileLog(LOGLEVEL level, const char* msg, ...);

        void setLogPath(QString logPath);         //defalut: current path

        void setLogLevel(LOGLEVEL logLevel);      //defalut: LOG_DEBUG

    private:

        static LogWriter * _logCenter;

        explicit LogWriter();

        ~LogWriter();

    private:

        QString _logPath;

        LOGLEVEL _logLevel;

    private:

        QString getLevelStr(LOGLEVEL level);

};
LogWriter *LogWriter::getLogCenter()

{

    if (_logCenter == NULL)

        _logCenter = new LogWriter;

    return _logCenter;

}

LogWriter::LogWriter()

{

    _logLevel = LOG_DEBUG;

    _logPath = QDir::currentPath();

}

LogWriter::~LogWriter()

{

    if (_logCenter) {

        delete _logCenter;

        _logCenter = NULL;

    }

}

void LogWriter::PrintLog(LOGLEVEL level, const char *msg,  ...)

{

    if (level < _logLevel)  return;     //low level

    char logBuffer[8192] = {0};

    va_list vl_fmt;                     //buffer

    va_start(vl_fmt, msg);

    vsprintf(logBuffer, msg, vl_fmt);

    va_end(vl_fmt);

    QString fileTime = "";

    QString logTime = "";

    QString logLevel = getLevelStr(level);

    fileTime = QDateTime::currentDateTime().toString("yyyyddMM");

    logTime = QDateTime::currentDateTime().toString("yyyy-dd-MM hh:mm:ss.zzz");

    qDebug("[%s] [%s] {%s}", logTime.toStdString().c_str(), logLevel.toStdString().c_str(), logBuffer);

}

void LogWriter::SaveFileLog(LOGLEVEL level, const char *msg,  ...)

{

    if (level < _logLevel)  return;  //low level

    char logBuffer[8192] = {0};

    va_list vl_fmt;                  //buff

    va_start(vl_fmt, msg);

    vsprintf(logBuffer, msg, vl_fmt);

    va_end(vl_fmt);

    QString logTime = "";

    QString fileTime = "";

    fileTime = QDateTime::currentDateTime().toString("yyyyddMM");

    logTime = QDateTime::currentDateTime().toString("[yyyy-dd-MM hh:mm:ss.zzz]");

    QString logLevel = getLevelStr(level);

    QString logFile = _logPath;

    if (logFile.right(1) != "/") {

        logFile += "/";

    }

    QDir mDir(logFile);

    if (!mDir.exists()) {

        mDir.mkpath(logFile);

    }

    logFile += "isoft_";

    logFile += fileTime;

    logFile += ".log";

    QFile file(logFile);

    file.open(QIODevice::ReadWrite | QIODevice::Append | QIODevice::Text);

    QTextStream out(&file);

    out << logTime << " [" << logLevel << "] " << "{" << logBuffer << "}" << endl;

    file.close();

}

QString LogWriter::getLevelStr(LOGLEVEL level)

{

    switch(level) {

        case LOG_DEBUG: return "LOG_DEBUG"; break;

        case LOG_INFO: return "LOG_INFO"; break;

        case LOG_WARN: return "LOG_WARN"; break;

        case LOG_ERROR: return "LOG_ERROR"; break;

    }

}

void LogWriter::setLogPath(QString logPath)

{

    _logPath = logPath;

}

void LogWriter::setLogLevel(LOGLEVEL logLevel)

{

    _logLevel = logLevel;

}

能够设置日志的级别和日志文件的路径。

在函数中使用： 

LogWriter::getLogCenter()->PrintLog(LOG_DEBUG, "hello world");

LogWriter::getLogCenter()->PrintLog(LOG_INFO, "%s:%s,%d", "hello", "world", 1234);

LogWriter::getLogCenter()->SaveFileLog(LOG_WARN, "hello world");

LogWriter::getLogCenter()->SaveFileLog(LOG_ERROR, "%s:%s,%d", "hello", "world", 1234);

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也会在当前路径下生成文件。

3、Qt自带样例

Qt官方样例： 

 #include <qapplication.h>

 #include <stdio.h>

 #include <stdlib.h>

 void myMessageOutput(QtMsgType type, const char *msg)

 {

     switch (type) {

     case QtDebugMsg:

         fprintf(stderr, "Debug: %s\n", msg);

         break;

     case QtWarningMsg:

         fprintf(stderr, "Warning: %s\n", msg);

         break;

     case QtCriticalMsg:

         fprintf(stderr, "Critical: %s\n", msg);

         break;

     case QtFatalMsg:

         fprintf(stderr, "Fatal: %s\n", msg);

         abort();

     }

 }

 int main(int argc, char **argv)

 {

     qInstallMsgHandler(myMessageOutput);

     QApplication app(argc, argv);

     ...

     return app.exec();

 }

自己定义改动： 

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:");

        abort();

    }

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

    QFile file("log.txt");

    file.open(QIODevice::WriteOnly | QIODevice::Append);

    QTextStream text_stream(&file);

    text_stream << message << endl;

    file.flush();

    file.close();

    mutex.unlock();

}
qInstallMsgHandler(outputMessage);

qWarning("This is a warning message");

qCritical("This is a critical message");

//qInstallMsgHandler(0)    //To restore the message handler, call

执行结果：

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三、总结

（1）本文仅仅是一个简单的日志记录。还能够设计成异步的多线程式的，甚至能够增加到线程池，对性能要求较高的系统还得考虑文件的大小控制、存储空间的控制、文件的级别控制、文件的日期控制和自己主动清除等操作。

（2）本人思路有限，若有更好的设计建议。也可发邮件沟通，在此先感谢。邮箱地址yang.ao@i-soft.com.cn。

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