Redirect qDebug to an emitted signal - c++

Question

I've successfully redirected qDebug() output to a QTextEdit widget. For several reasons, I'd like every qDebug() message to be included in an emitted signal. One reason is that the object which shall receive the output isn't available. Another reason is that I want to redirect the output to different objects depending on which activity is active at the moment (using connect/disconnect of the signal to different slots).
I've made a working example code that redirects qDebug to a QTextEdit widget. Can someone please help me to get this code to emit a signal which includes the qDebug message?
I'm not sure if its possible to have Q_DebugStream emit a signal (I've tried and failed to make a Qt Class out of it).
It must be possible to pass a pointer to a function/slot instead of a pointer to a QTextEdit when calling Q_DebugStream, but I'm not sure how this is done.
mainwindow.h:
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QTextEdit>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = 0);
~MainWindow();
signals:
void logSignal(QString);
public slots:
void logSlot(QString);
private:
QTextEdit *logView;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "q_debugstream.h"
#include <QGridLayout>
#include <QDebug>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
QWidget *mainWidget = new QWidget(this);
setCentralWidget(mainWidget);
logView = new QTextEdit;
QGridLayout *mainLayout = new QGridLayout;
mainLayout->addWidget(logView,0,0,1,1);
mainWidget->setLayout(mainLayout);
connect(this, SIGNAL(logSignal(QString)),
this, SLOT(logSlot(QString)));
emit logSignal("Message from a signal\n");
new Q_DebugStream(std::cout, logView); //Redirect Console output to QTextEdit
Q_DebugStream::registerQDebugMessageHandler(); //Redirect qDebug() output to QTextEdit
qDebug() << "DEBUG MODE ACTIVE";
}
MainWindow::~MainWindow(){}
void MainWindow::logSlot(QString log) {
logView->append(log);
}
q_debugstream.h
//As per forum:
//http://www.qtforum.org/article/39768/redirecting-std-cout-std-cerf-qdebug-to-qtextedit.html
//A couple of lines added to ensure newlines go between each call.
//Thanks, James!
#ifndef Q_DEBUGSTREAM_H
#define Q_DEBUGSTREAM_H
#include <iostream>
#include <streambuf>
#include <string>
#include <QTextEdit>
class Q_DebugStream : public std::basic_streambuf<char>
{
public:
Q_DebugStream(std::ostream &stream, QTextEdit* text_edit) : m_stream(stream)
{
log_window = text_edit;
m_old_buf = stream.rdbuf();
stream.rdbuf(this);
}
~Q_DebugStream()
{
m_stream.rdbuf(m_old_buf);
}
static void registerQDebugMessageHandler(){
qInstallMessageHandler(myQDebugMessageHandler);
}
private:
static void myQDebugMessageHandler(QtMsgType, const QMessageLogContext &, const QString &msg)
{
std::cout << msg.toStdString().c_str();
}
protected:
//This is called when a std::endl has been inserted into the stream
virtual int_type overflow(int_type v)
{
if (v == '\n')
{
log_window->append("");
}
return v;
}
virtual std::streamsize xsputn(const char *p, std::streamsize n)
{
QString str(p);
if(str.contains("\n")){
QStringList strSplitted = str.split("\n");
log_window->moveCursor (QTextCursor::End);
log_window->insertPlainText (strSplitted.at(0)); //Index 0 is still on the same old line
for(int i = 1; i < strSplitted.size(); i++){
log_window->append(strSplitted.at(i));
log_window->append("\n");
}
}else{
log_window->moveCursor (QTextCursor::End);
log_window->insertPlainText (str);
log_window->insertPlainText ("\n");
}
return n;
}
private:
std::ostream &m_stream;
std::streambuf *m_old_buf;
QTextEdit* log_window;
};
#endif // Q_DEBUGSTREAM_H
When application is started, I get both messages in my QTextEdit:
"Message from a signal"
"DEBUG MODE ACTIVE"

Answer 1

(This answer extracted from an edit to the question - now rolled back).
Here's how I solved this:
mainwindow.h:
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QTextEdit>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = 0);
~MainWindow();
signals:
void logSignal(QString);
public slots:
void logSlot(QString);
private:
void dbgMsg(QString);
QTextEdit *logView;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "q_debugstream.h"
#include <QGridLayout>
#include <QDebug>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
QWidget *mainWidget = new QWidget(this);
setCentralWidget(mainWidget);
logView = new QTextEdit;
QGridLayout *mainLayout = new QGridLayout;
mainLayout->addWidget(logView,0,0,1,1);
mainWidget->setLayout(mainLayout);
connect(this, SIGNAL(logSignal(QString)),
this, SLOT(logSlot(QString)));
emit logSignal("Now call Q_DebugStream");
//Redirect qDebug() output to dbgMsg(QString)
new Q_DebugStream(std::cout, this, &MainWindow::dbgMsg);
Q_DebugStream::registerQDebugMessageHandler();
qDebug() << "Debug message";
qWarning() << "Warning!";
qCritical() << "Critical issue!";
qInfo() << "Information";
qDebug() << "This\nis\na\nlong\none.";
}
MainWindow::~MainWindow(){}
void MainWindow::logSlot(QString log) {
logView->append(log);
}
void MainWindow::dbgMsg(QString log) {
emit logSignal(log);
}
q_debugstream.h
#ifndef Q_DEBUGSTREAM_H
#define Q_DEBUGSTREAM_H
#include <iostream>
#include <streambuf>
#include <string>
#include <QString>
#include "mainwindow.h"
class Q_DebugStream : public std::basic_streambuf<char> {
public:
Q_DebugStream(std::ostream &stream, MainWindow* obj, void (MainWindow::*dbgMsgPtr)(QString log)): m_stream(stream) {
m_old_buf = stream.rdbuf();
stream.rdbuf(this);
msgObj = obj;
msgHandler = dbgMsgPtr;
}
~Q_DebugStream() {
m_stream.rdbuf(m_old_buf);
}
static void registerQDebugMessageHandler() {
qInstallMessageHandler(myQDebugMessageHandler);
}
private:
static void myQDebugMessageHandler(QtMsgType type, const QMessageLogContext &context, const QString &msg) {
QString message = msg;
switch (type) {
case QtDebugMsg:
message.prepend("qDbg(): ");
break;
case QtWarningMsg:
message.prepend("qWarn(): ");
break;
case QtCriticalMsg:
message.prepend("qCrit(): ");
break;
case QtInfoMsg:
message.prepend("qInfo(): ");
break;
case QtFatalMsg:
message.prepend("qFatal(): ");
abort();
break;
}
message.append(" (" + QString::fromUtf8(context.file) + ")");
message.append(" line: " + QString::number(context.line));
std::cout << message.toStdString().c_str();
}
protected:
//This is called when a std::endl has been inserted into the stream
virtual int_type overflow(int_type v) {
if (v == '\n') {
(msgObj->*msgHandler)("\n");
}
return v;
}
virtual std::streamsize xsputn(const char *p, std::streamsize n) {
QString str(p);
if(str.contains("\n")) {
QStringList strSplitted = str.split("\n");
(msgObj->*msgHandler)(strSplitted.at(0)); //Index 0 is still on the same old line
for(int i = 1; i < strSplitted.size(); i++) {
(msgObj->*msgHandler)("\\ " + strSplitted.at(i));
}
} else {
(msgObj->*msgHandler)(str);
}
return n;
}
private:
std::ostream &m_stream;
std::streambuf *m_old_buf;
MainWindow* msgObj;
void (MainWindow::*msgHandler)(QString);
};
#endif // Q_DEBUGSTREAM_H
When application is started, I get these messages in my QTextEdit:
Now call Q_DebugStream
qDbg(): Debug message (..\qDebugFetch\mainwindow.cpp) line: 25
qWarn(): Warning! (..\qDebugFetch\mainwindow.cpp) line: 26
qCrit(): Critical issue! (..\qDebugFetch\mainwindow.cpp) line: 27
qInfo(): Information (..\qDebugFetch\mainwindow.cpp) line: 28
qDbg(): This
\ is
\ a
\ long
\ one. (..\qDebugFetch\mainwindow.cpp) line: 29