A class which allows for using a Rich Text Control Box from the wxWidgets library to be used as logging output. It also supports logging into a file and saving the previous log file.

wxRTLogger.cpp

#include "wxRTLogger.hpp"

wxRTLogger::wxRTLogger(std::string name, wxRichTextCtrl* wxRTBox) {
    this->richTextBox = wxRTBox;
    this->progName = name;

    this->richTextBox->BeginTextColour(wxColour(0,0,0));
    this->richTextBox->WriteText(_(this->progName + "\n\n"));
    this->richTextBox->EndTextColour();
}

wxRTLogger::~wxRTLogger() {
    this->richTextBox = NULL;
    this->logFile.close();
}

void wxRTLogger::info(std::string msg) { this->log(std::string("[INFO] ") + msg, wxRTLogger::LogLevel::INFO); }
void wxRTLogger::notice(std::string msg) { this->log(std::string("[NOTICE] ") + msg, wxRTLogger::LogLevel::NOTICE); }
void wxRTLogger::warning(std::string msg) { this->log(std::string("[WARNING] ") + msg, wxRTLogger::LogLevel::WARNING); }
void wxRTLogger::severe(std::string msg) { this->log(std::string("[SEVERE] ") + msg, wxRTLogger::LogLevel::SEVERE); }

void wxRTLogger::formatLine(wxRichTextCtrl* wxRTBox, wxRTLogger::LogLevel lvl) {
    std::string box = "  ";
    wxRichTextAttr attr;
    attr.SetFlags(wxTEXT_ATTR_BACKGROUND_COLOUR);

    if( lvl == wxRTLogger::LogLevel::INFO ) {
        wxRTBox->BeginTextColour(wxColour(0,0,0));
    } else if( lvl == wxRTLogger::LogLevel::NOTICE ) {
        wxRTBox->BeginItalic();
        wxRTBox->BeginTextColour(wxColour(96,32,192));
    } else if( lvl == wxRTLogger::LogLevel::WARNING ) {
        attr.SetBackgroundColour(wxColour(255,255,128));
        wxRTBox->BeginStyle(attr);
        wxRTBox->BeginTextColour(wxColour(0,0,192));
    } else if( lvl == wxRTLogger::LogLevel::SEVERE ) {
        attr.SetBackgroundColour(wxColour(255,0,0));
        wxRTBox->BeginBold();
        wxRTBox->BeginItalic();
        attr.SetBackgroundColour(wxColour(255,0,0));
        wxRTBox->BeginStyle(attr);
        wxRTBox->BeginTextColour(wxColour(255,255,255));
    }
}

const std::string wxRTLogger::currentDateTime() {
    time_t     now = time(0);
    struct tm  tstruct;
    char       buf[80];
    tstruct = *localtime(&now);
    strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", &tstruct);

    return std::string(buf);
}

void wxRTLogger::log(std::string msg, LogLevel lvl) {
    std::string line = this->currentDateTime() + " " + msg + "\n";

    this->richTextBox->SetInsertionPoint(this->richTextBox->GetLastPosition());
    this->formatLine(this->richTextBox, lvl);
    this->richTextBox->WriteText(_(line));
    this->richTextBox->EndAllStyles();

    if( this->logFile.is_open() ) {
        this->logFile << line;
        this->logFile.flush();
    }
}

void wxRTLogger::setLogFile(std::string fileName) {
    std::ifstream logFile;
    logFile.open(std::string(fileName + ".txt").c_str());
    if( logFile.good() ) {
        std::ofstream prevLog;
        prevLog.open(std::string(fileName + ".prev.txt").c_str(), std::ios::out | std::ios::trunc);
        prevLog << logFile.rdbuf();
        prevLog.close();
    }
    logFile.close();

    this->logFile.open(std::string(fileName + ".txt").c_str(), std::ios::out | std::ios::trunc);
}

void wxRTLogger::openLogFile(std::string fileName, wxRichTextCtrl* wxRTBox) {
    wxRTBox->Clear();
    std::ifstream ifile(std::string(fileName + ".txt").c_str());
    if( ifile.is_open() ) {
        while( ifile.good() ) {
            std::string line;
            wxColour clr;

            std::getline(ifile, line);

            if( line.find_first_of('[') != std::string::npos && line.find_first_of(']') != std::string::npos ) {
                std::string type(line.substr(line.find_first_of('[')+1, line.find_first_of(']')-line.find_first_of('[')-1));
                this->formatLine(wxRTBox,
                                    type == "SEVERE" ? wxRTLogger::LogLevel::SEVERE :
                                     type == "WARNING" ? wxRTLogger::LogLevel::WARNING :
                                      type == "NOTICE" ? wxRTLogger::LogLevel::NOTICE :
                                       wxRTLogger::LogLevel::INFO);
            }

            wxRTBox->BeginTextColour(clr);
            wxRTBox->WriteText(_(line + "\n"));
            wxRTBox->EndAllStyles();
        }
    }
    ifile.close();
}

wxRTLogger.hpp

#ifndef WXRTLOGGER_HPP
#define WXRTLOGGER_HPP

#include <iostream>
#include <fstream>
#include <string>
#include <stdio.h>
#include <time.h>
#include <wx/richtext/richtextctrl.h>
#include <wx/richtext/richtextbuffer.h>

class wxRTLogger
{
    public:
        wxRTLogger(std::string name, wxRichTextCtrl* wxRTBox);
        virtual ~wxRTLogger();
        virtual void info(std::string msg);
        virtual void notice(std::string msg);
        virtual void warning(std::string msg);
        virtual void severe(std::string msg);
        virtual void setLogFile(std::string fileName);
        virtual void openLogFile(std::string fileName, wxRichTextCtrl* wxRTBox);
        enum LogLevel { INFO, NOTICE, WARNING, SEVERE };
    private:
        wxRichTextCtrl* richTextBox;
        std::string progName;
        std::ofstream logFile;
        virtual void log(std::string msg, LogLevel lvl);
        virtual const std::string currentDateTime();
        virtual void formatLine(wxRichTextCtrl* wxRTBox, wxRTLogger::LogLevel lvl);
};

#endif // WXRTLOGGER_HPP