QTextStream interpreted constant by gcc

[champax]

Hello everyone. I'm new on Qt, and I'm working on Ubuntu 18 Qt5.15.2. I use gcc for debogging.
As part of my project, I wanted to develop my own logger. In this context, I create a Loggin object, which instantiate a LoggerLog object, witch record in real time data in a log file. The Loggin object create e LoggerTerminal object too, which displays with coloring in real time the equivalent in the terminal.

These 2 instances inherit from a virtual class named Logger.

In the write method of LoggerLog, I use a QTextSteam created by my constructor. This QTextStream is itself defined as a variable and not a constant. However, when debugging, I see that the compiler defines it as a constant, which prevents me from using it beyond the constructor.

Sorry, it's a lot of files extracts, but I simplified them to the maximum.

logger.h

#ifndef LOGGER_H
#define LOGGER_H

//Qt += core
#include <QString>

//SL
#include <string>

enum importance_level:  quint8 {critical, v_important, important, normal};
enum type_event:        quint8 {error, alert, success, failure, instruction};

class Logger
{
  public:
    virtual ~Logger(){}
    virtual void write( const QString&,
                        const importance_level level = importance_level::normal,
                        const type_event type = type_event::instruction) const = 0;
    virtual QString get_level(importance_level level) const 
    {
      switch(level)
      {
        case importance_level::normal:
          return "";
        
        case importance_level::important:
          return "IMPORTANT: ";
      }
    }
    virtual QString get_type(type_event type) const
    {
      switch(type)
      {
        case type_event::instruction:
          return "INSTRUCTION: ";
        
        case type_event::failure:
          return "FAILURE: ";
      }
    }

  protected:
    const QString m_T_format = "hh:mm:ss";
    const QString m_DT_format = "ddd d MMMM yyyy hh:mm:ss";
};

#endif // LOGGER_H

loggerLog.h

#ifndef LOGGERLOG_H
#define LOGGERLOG_H

// QT += core
#include <QtCore>
#include <QFile>
#include <QTextStream>
#include <QDataStream>

//virtual class
#include "logger.h"

class LoggerLog : public Logger
{
    public:
        LoggerLog(const QString name_logFile);   
        virtual ~LoggerLog();
        virtual void write( const QString& msg,
                            const importance_level level = importance_level::normal,
                            const type_event type = type_event::instruction) const;
        
    private:
        QFile m_logFile;
        QTextStream m_out;
};

#endif //LOGGERLOG_H

loggerLog.cpp

#include "loggerLog.h"

LoggerLog::LoggerLog(const QString name_logFile)
    : m_logFile(name_logFile), m_out(&m_logFile)
{
    m_logFile.open(QFile::WriteOnly | QFile::Truncate);
    m_out   << " =============================================== \n"
            << "    Begin Output log :\n"
            << "         - " << QDateTime::currentDateTime().toString(m_DT_format) << '\n'
            << " =============================================== \n\n";
}

LoggerLog::~LoggerLog()
{
    m_out   << '\n'
            << " =============================================== \n"
            << "    End   Output log :\n"
            << "         - " << QDateTime::currentDateTime().toString(m_DT_format) << '\n'
            << " =============================================== \n\n";
}


void LoggerLog::write(  const QString& msg,
                        const importance_level level,
                        const type_event type) const
{
    m_out   << ' ' << QTime::currentTime().toString(m_T_format) << ":   - " 
            << get_level(level) << get_type(type) << msg << '\n';
}

my terminal output :

$ ./compile_logger.bash 
../../src/log/loggerLog.cpp: In member function ‘virtual void LoggerLog::write(const QString&, importance_level, type_event) const’:
../../src/log/loggerLog.cpp:42:13: error: no match for ‘operator<<’ (operand types are ‘const QTextStream’ and ‘QString’)
     m_out   << QTime::currentTime().toString(m_T_format) << ":   - "
     ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you have any idea of the reason of this interpretation, or a solution to avoid this QTextStream to pass constant, it would be very nice. Thank's in advance !!

Champax

[Christian Ehrlicher]

Your write() function is const so the members are const too - basic c++. Make you function non-const.

[sierdzio]

@champax said in QTextStream interpreted constant by gcc:

void LoggerLog::write( const QString& msg,
const importance_level level,
const type_event type) const

Your method is const but you are trying to modify a member variable m_out inside of it.

Change write() to be non-const and it will work.