path: root/src/corelib/global/qlogging.cpp

/****************************************************************************
**
** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/
**
** This file is part of the QtCore module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** GNU Lesser General Public License Usage
** This file may be used under the terms of the GNU Lesser General Public
** License version 2.1 as published by the Free Software Foundation and
** appearing in the file LICENSE.LGPL included in the packaging of this
** file. Please review the following information to ensure the GNU Lesser
** General Public License version 2.1 requirements will be met:
** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights. These rights are described in the Nokia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU General
** Public License version 3.0 as published by the Free Software Foundation
** and appearing in the file LICENSE.GPL included in the packaging of this
** file. Please review the following information to ensure the GNU General
** Public License version 3.0 requirements will be met:
** http://www.gnu.org/copyleft/gpl.html.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms and
** conditions contained in a signed written agreement between you and Nokia.
**
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/

#include "qlogging.h"
#include "qlist.h"
#include "qbytearray.h"
#include "qstring.h"
#include "qvarlengtharray.h"
#include "qdebug.h"
#ifndef QT_BOOTSTRAPPED
#include "qcoreapplication.h"
#include "qthread.h"
#endif
#ifdef Q_OS_WINCE
#include <qt_windows.h>
#endif

#include <stdio.h>

QT_BEGIN_NAMESPACE

/*!
    \class QMessageLogContext
    \relates <QtGlobal>
    \brief The QMessageLogContext class provides additional information about a log message.
    \since 5.0

    The class provides information about the source code location a qDebug(), qWarning(),
    qCritical() or qFatal() message was generated.

    \sa QMessageLogger, QMessageHandler, qInstallMessageHandler()
*/

/*!
    \class QMessageLogger
    \relates <QtGlobal>
    \brief The QMessageLogger class generates log messages.
    \since 5.0

    QMessageLogger is used to generate messages for the Qt logging framework. Most of the time
    is transparently used through the qDebug(), qWarning(), qCritical, or qFatal() functions,
    which are actually macros that expand to QMessageLogger(__FILE__, __LINE__, Q_FUNC_INFO).debug()
    et al.

    One example of direct use is to forward errors that stem from a scripting language, e.g. QML:

    \snippet doc/src/snippets/code/qlogging/qlogging.cpp 1

    \sa QMessageLogContext, qDebug(), qWarning(), qCritical(), qFatal()
*/

#if !defined(QT_NO_EXCEPTIONS)
/*!
    \internal
    Uses a local buffer to output the message. Not locale safe + cuts off
    everything after character 255, but will work in out of memory situations.
*/
static void qEmergencyOut(QtMsgType msgType, const char *msg, va_list ap)
{
    char emergency_buf[256] = { '\0' };
    emergency_buf[255] = '\0';
    if (msg)
        qvsnprintf(emergency_buf, 255, msg, ap);
    QMessageLogContext context;
    qt_message_output(msgType, context, emergency_buf);
}
#endif

/*!
    \internal
*/
static void qt_message(QtMsgType msgType, const QMessageLogContext &context, const char *msg,
                       va_list ap)
{
#if !defined(QT_NO_EXCEPTIONS)
    if (std::uncaught_exception()) {
        qEmergencyOut(msgType, msg, ap);
        return;
    }
#endif
    QByteArray buf;
    if (msg) {
        QT_TRY {
            buf = QString().vsprintf(msg, ap).toLocal8Bit();
        } QT_CATCH(const std::bad_alloc &) {
#if !defined(QT_NO_EXCEPTIONS)
            qEmergencyOut(msgType, msg, ap);
            // don't rethrow - we use qWarning and friends in destructors.
            return;
#endif
        }
    }
    qt_message_output(msgType, context, buf.constData());
}

#undef qDebug
/*!
    \fn qDebug(const char *message, ...)
    \relates <QtGlobal>

    Calls the message handler with the debug message \a msg. If no
    message handler has been installed, the message is printed to
    stderr. Under Windows, the message is sent to the console, if it is a
    console application; otherwise, it is sent to the debugger. This
    function does nothing if \c QT_NO_DEBUG_OUTPUT was defined
    during compilation.

    If you pass the function a format string and a list of arguments,
    it works in similar way to the C printf() function. The format
    should be a Latin-1 string.

    Example:

    \snippet doc/src/snippets/code/src_corelib_global_qglobal.cpp 24

    If you include \c <QtDebug>, a more convenient syntax is also
    available:

    \snippet doc/src/snippets/code/src_corelib_global_qglobal.cpp 25

    With this syntax, the function returns a QDebug object that is
    configured to use the QtDebugMsg message type. It automatically
    puts a single space between each item, and outputs a newline at
    the end. It supports many C++ and Qt types.

    To suppress the output at run-time, install your own message handler
    with qInstallMessageHandler().

    \sa qWarning(), qCritical(), qFatal(), qInstallMessageHandler(),
        {Debugging Techniques}
*/

void QMessageLogger::debug(const char *msg, ...)
{
    va_list ap;
    va_start(ap, msg); // use variable arg list
    qt_message(QtDebugMsg, context, msg, ap);
    va_end(ap);
}

#ifndef QT_NO_DEBUG_STREAM

QDebug QMessageLogger::debug()
{
    QDebug dbg = QDebug(QtDebugMsg);
    QMessageLogContext &ctxt = dbg.stream->context;
    ctxt.file = context.file;
    ctxt.line = context.line;
    ctxt.function = context.function;
    return dbg;
}

QNoDebug QMessageLogger::noDebug()
{
    return QNoDebug();
}

#endif

#undef qWarning
/*!
    \fn qWarning(const char *message, ...)
    \relates <QtGlobal>

    Calls the message handler with the warning message \a msg. If no
    message handler has been installed, the message is printed to
    stderr. Under Windows, the message is sent to the debugger. This
    function does nothing if \c QT_NO_WARNING_OUTPUT was defined
    during compilation; it exits if the environment variable \c
    QT_FATAL_WARNINGS is defined.

    This function takes a format string and a list of arguments,
    similar to the C printf() function. The format should be a Latin-1
    string.

    Example:
    \snippet doc/src/snippets/code/src_corelib_global_qglobal.cpp 26

    If you include <QtDebug>, a more convenient syntax is
    also available:

    \snippet doc/src/snippets/code/src_corelib_global_qglobal.cpp 27

    This syntax inserts a space between each item, and
    appends a newline at the end.

    To suppress the output at runtime, install your own message handler
    with qInstallMessageHandler().

    \sa qDebug(), qCritical(), qFatal(), qInstallMessageHandler(),
        {Debugging Techniques}
*/

void QMessageLogger::warning(const char *msg, ...)
{
    va_list ap;
    va_start(ap, msg); // use variable arg list
    qt_message(QtWarningMsg, context, msg, ap);
    va_end(ap);
}

#ifndef QT_NO_DEBUG_STREAM
QDebug QMessageLogger::warning()
{
    QDebug dbg = QDebug(QtWarningMsg);
    QMessageLogContext &ctxt = dbg.stream->context;
    ctxt.file = context.file;
    ctxt.line = context.line;
    ctxt.function = context.function;
    return dbg;
}
#endif

#undef qCritical
/*!
    \fn qCritical(const char *message, ...)
    \relates <QtGlobal>

    Calls the message handler with the critical message \a msg. If no
    message handler has been installed, the message is printed to
    stderr. Under Windows, the message is sent to the debugger.

    This function takes a format string and a list of arguments,
    similar to the C printf() function. The format should be a Latin-1
    string.

    Example:
    \snippet doc/src/snippets/code/src_corelib_global_qglobal.cpp 28

    If you include <QtDebug>, a more convenient syntax is
    also available:

    \snippet doc/src/snippets/code/src_corelib_global_qglobal.cpp 29

    A space is inserted between the items, and a newline is
    appended at the end.

    To suppress the output at runtime, install your own message handler
    with qInstallMessageHandler().

    \sa qDebug(), qWarning(), qFatal(), qInstallMessageHandler(),
        {Debugging Techniques}
*/

void QMessageLogger::critical(const char *msg, ...)
{
    va_list ap;
    va_start(ap, msg); // use variable arg list
    qt_message(QtCriticalMsg, context, msg, ap);
    va_end(ap);
}

#ifndef QT_NO_DEBUG_STREAM
QDebug QMessageLogger::critical()
{
    QDebug dbg = QDebug(QtCriticalMsg);
    QMessageLogContext &ctxt = dbg.stream->context;
    ctxt.file = context.file;
    ctxt.line = context.line;
    ctxt.function = context.function;
    return dbg;
}
#endif

#undef qFatal
/*!
    \fn qFatal(const char *message, ...)
    \relates <QtGlobal>

    Calls the message handler with the fatal message \a msg. If no
    message handler has been installed, the message is printed to
    stderr. Under Windows, the message is sent to the debugger.

    If you are using the \b{default message handler} this function will
    abort on Unix systems to create a core dump. On Windows, for debug builds,
    this function will report a _CRT_ERROR enabling you to connect a debugger
    to the application.

    This function takes a format string and a list of arguments,
    similar to the C printf() function.

    Example:
    \snippet doc/src/snippets/code/src_corelib_global_qglobal.cpp 30

    To suppress the output at runtime, install your own message handler
    with qInstallMessageHandler().

    \sa qDebug(), qCritical(), qWarning(), qInstallMessageHandler(),
        {Debugging Techniques}
*/

void QMessageLogger::fatal(const char *msg, ...)
{
    va_list ap;
    va_start(ap, msg); // use variable arg list
    qt_message(QtFatalMsg, context, msg, ap);
    va_end(ap);
}

/*!
    \internal
*/
Q_AUTOTEST_EXPORT QByteArray qCleanupFuncinfo(QByteArray info)
{
    // Strip the function info down to the base function name
    // note that this throws away the template definitions,
    // the parameter types (overloads) and any const/volatile qualifiers.

    if (info.isEmpty())
        return info;

    int pos;

    // skip trailing [with XXX] for templates (gcc)
    pos = info.size() - 1;
    if (info.endsWith(']')) {
        while (--pos) {
            if (info.at(pos) == '[')
                info.truncate(pos);
        }
    }

    // operator names with '(', ')', '<', '>' in it
    static const char operator_call[] = "operator()";
    static const char operator_lessThan[] = "operator<";
    static const char operator_greaterThan[] = "operator>";
    static const char operator_lessThanEqual[] = "operator<=";
    static const char operator_greaterThanEqual[] = "operator>=";

    // canonize operator names
    info.replace("operator ", "operator");

    // remove argument list
    forever {
        int parencount = 0;
        pos = info.lastIndexOf(')');
        if (pos == -1) {
            // Don't know how to parse this function name
            return info;
        }

        // find the beginning of the argument list
        --pos;
        ++parencount;
        while (pos && parencount) {
            if (info.at(pos) == ')')
                ++parencount;
            else if (info.at(pos) == '(')
                --parencount;
            --pos;
        }
        if (parencount != 0)
            return info;

        info.truncate(++pos);

        if (info.at(pos - 1) == ')') {
            if (info.indexOf(operator_call) == pos - (int)strlen(operator_call))
                break;

            // this function returns a pointer to a function
            // and we matched the arguments of the return type's parameter list
            // try again
            info.remove(0, info.indexOf('('));
            info.chop(1);
            continue;
        } else {
            break;
        }
    }

    // find the beginning of the function name
    int parencount = 0;
    int templatecount = 0;
    --pos;

    // make sure special characters in operator names are kept
    if (pos > -1) {
        switch (info.at(pos)) {
        case ')':
            if (info.indexOf(operator_call) == pos - (int)strlen(operator_call) + 1)
                pos -= 2;
            break;
        case '<':
            if (info.indexOf(operator_lessThan) == pos - (int)strlen(operator_lessThan) + 1)
                --pos;
            break;
        case '>':
            if (info.indexOf(operator_greaterThan) == pos - (int)strlen(operator_greaterThan) + 1)
                --pos;
            break;
        case '=': {
            int operatorLength = (int)strlen(operator_lessThanEqual);
            if (info.indexOf(operator_lessThanEqual) == pos - operatorLength + 1)
                pos -= 2;
            else if (info.indexOf(operator_greaterThanEqual) == pos - operatorLength + 1)
                pos -= 2;
            break;
        }
        default:
            break;
        }
    }

    while (pos > -1) {
        if (parencount < 0 || templatecount < 0)
            return info;

        char c = info.at(pos);
        if (c == ')')
            ++parencount;
        else if (c == '(')
            --parencount;
        else if (c == '>')
            ++templatecount;
        else if (c == '<')
            --templatecount;
        else if (c == ' ' && templatecount == 0 && parencount == 0)
            break;

        --pos;
    }
    info = info.mid(pos + 1);

    // remove trailing '*', '&' that are part of the return argument
    while ((info.at(0) == '*')
           || (info.at(0) == '&'))
        info = info.mid(1);

    // we have the full function name now.
    // clean up the templates
    while ((pos = info.lastIndexOf('>')) != -1) {
        if (!info.contains('<'))
            break;

        // find the matching close
        int end = pos;
        templatecount = 1;
        --pos;
        while (pos && templatecount) {
            register char c = info.at(pos);
            if (c == '>')
                ++templatecount;
            else if (c == '<')
                --templatecount;
            --pos;
        }
        ++pos;
        info.remove(pos, end - pos + 1);
    }

    return info;
}

// tokens as recognized in QT_MESSAGE_PATTERN
static const char typeTokenC[] = "%{type}";
static const char messageTokenC[] = "%{message}";
static const char fileTokenC[] = "%{file}";
static const char lineTokenC[] = "%{line}";
static const char functionTokenC[] = "%{function}";
static const char pidTokenC[] = "%{pid}";
static const char appnameTokenC[] = "%{appname}";
static const char threadidTokenC[] = "%{threadid}";
static const char emptyTokenC[] = "";

struct QMessagePattern {
    QMessagePattern();
    ~QMessagePattern();

    // 0 terminated arrays of literal tokens / literal or placeholder tokens
    const char **literals;
    const char **tokens;
};

QMessagePattern::QMessagePattern()
{
    QString pattern = QString::fromLocal8Bit(qgetenv("QT_MESSAGE_PATTERN"));
    if (pattern.isEmpty()) {
        pattern = QLatin1String("%{message}");
    }

    // scanner
    QList<QString> lexemes;
    QString lexeme;
    bool inPlaceholder = false;
    for (int i = 0; i < pattern.size(); ++i) {
        const QChar c = pattern.at(i);
        if ((c == QLatin1Char('%'))
                && !inPlaceholder) {
            if ((i + 1 < pattern.size())
                    && pattern.at(i + 1) == QLatin1Char('{')) {
                // beginning of placeholder
                if (!lexeme.isEmpty()) {
                    lexemes.append(lexeme);
                    lexeme.clear();
                }
                inPlaceholder = true;
            }
        }

        lexeme.append(c);

        if ((c == QLatin1Char('}') && inPlaceholder)) {
            // end of placeholder
            lexemes.append(lexeme);
            lexeme.clear();
            inPlaceholder = false;
        }
    }
    if (!lexeme.isEmpty())
        lexemes.append(lexeme);

    // tokenizer
    QVarLengthArray<const char*> literalsVar;
    tokens = new const char*[lexemes.size() + 1];
    tokens[lexemes.size()] = 0;

    for (int i = 0; i < lexemes.size(); ++i) {
        const QString lexeme = lexemes.at(i);
        if (lexeme.startsWith(QLatin1String("%{"))
                && lexeme.endsWith(QLatin1Char('}'))) {
            // placeholder
            if (lexeme == QLatin1String(typeTokenC)) {
                tokens[i] = typeTokenC;
            } else if (lexeme == QLatin1String(messageTokenC))
                tokens[i] = messageTokenC;
            else if (lexeme == QLatin1String(fileTokenC))
                tokens[i] = fileTokenC;
            else if (lexeme == QLatin1String(lineTokenC))
                tokens[i] = lineTokenC;
            else if (lexeme == QLatin1String(functionTokenC))
                tokens[i] = functionTokenC;
            else if (lexeme == QLatin1String(pidTokenC))
                tokens[i] = pidTokenC;
            else if (lexeme == QLatin1String(appnameTokenC))
                tokens[i] = appnameTokenC;
            else if (lexeme == QLatin1String(threadidTokenC))
                tokens[i] = threadidTokenC;
            else {
                fprintf(stderr, "%s\n",
                        QString::fromLatin1("QT_MESSAGE_PATTERN: Unknown placeholder %1\n"
                                            ).arg(lexeme).toLocal8Bit().constData());
                fflush(stderr);
                tokens[i] = emptyTokenC;
            }
        } else {
            char *literal = new char[lexeme.size() + 1];
            strncpy(literal, lexeme.toLocal8Bit().constData(), lexeme.size());
            literal[lexeme.size()] = '\0';
            literalsVar.append(literal);
            tokens[i] = literal;
        }
    }
    literals = new const char*[literalsVar.size() + 1];
    literals[literalsVar.size()] = 0;
    memcpy(literals, literalsVar.constData(), literalsVar.size() * sizeof(const char*));
}

QMessagePattern::~QMessagePattern()
{
    for (int i = 0; literals[i] != 0; ++i)
        delete [] literals[i];
    delete [] literals;
    literals = 0;
    delete [] tokens;
    tokens = 0;
}

Q_GLOBAL_STATIC(QMessagePattern, qMessagePattern)

/*!
    \internal
*/
Q_CORE_EXPORT QByteArray qMessageFormatString(QtMsgType type, const QMessageLogContext &context,
                                              const char *str)
{
    QByteArray message;

    QMessagePattern *pattern = qMessagePattern();
    if (!pattern) {
        // after destruction of static QMessagePattern instance
        message.append(str);
        message.append('\n');
        return message;
    }

    // we do not convert file, function, line literals to local encoding due to overhead
    for (int i = 0; pattern->tokens[i] != 0; ++i) {
        const char *token = pattern->tokens[i];
        if (token == messageTokenC) {
            message.append(str);
        } else if (token == typeTokenC) {
            switch (type) {
            case QtDebugMsg:   message.append("debug"); break;
            case QtWarningMsg: message.append("warning"); break;
            case QtCriticalMsg:message.append("critical"); break;
            case QtFatalMsg:   message.append("fatal"); break;
            }
        } else if (token == fileTokenC) {
            if (context.file)
                message.append(context.file);
            else
                message.append("unknown");
        } else if (token == lineTokenC) {
            message.append(QByteArray::number(context.line));
        } else if (token == functionTokenC) {
            if (context.function)
                message.append(qCleanupFuncinfo(context.function));
            else
                message.append("unknown");
#ifndef QT_BOOTSTRAPPED
        } else if (token == pidTokenC) {
            message.append(QByteArray::number(QCoreApplication::applicationPid()));
        } else if (token == appnameTokenC) {
            message.append(QCoreApplication::applicationName().toUtf8().constData());
        } else if (token == threadidTokenC) {
            message.append("0x" + QByteArray::number(qlonglong(QThread::currentThread()->currentThread()), 16));
#endif
        } else {
            message.append(token);
        }
    }
    message.append('\n');
    return message;
}

static QtMsgHandler msgHandler = 0;                // pointer to debug handler (without context)
static QMessageHandler messageHandler = 0;         // pointer to debug handler (with context)

/*!
    \internal
*/
static void qDefaultMessageHandler(QtMsgType type, const QMessageLogContext &context,
                                   const char *buf)
{
    QByteArray logMessage = qMessageFormatString(type, context, buf);
#if defined(Q_OS_WINCE)
    QString fstr = QString::fromLocal8Bit(logMessage);
    OutputDebugString(reinterpret_cast<const wchar_t *> (fstr.utf16()));
#else
    fprintf(stderr, "%s", logMessage.constData());
    fflush(stderr);
#endif
}

/*!
    \internal
*/
static void qDefaultMsgHandler(QtMsgType type, const char *buf)
{
    QMessageLogContext emptyContext;
    qDefaultMessageHandler(type, emptyContext, buf);
}

/*!
    \internal
*/
void qt_message_output(QtMsgType msgType, const QMessageLogContext &context, const char *buf)
{
    if (!msgHandler)
        msgHandler = qDefaultMsgHandler;
    if (!messageHandler)
        messageHandler = qDefaultMessageHandler;

    // prefer new message handler over the old one
    if (msgHandler == qDefaultMsgHandler
            || messageHandler != qDefaultMessageHandler) {
        (*messageHandler)(msgType, context, buf);
    } else {
        (*msgHandler)(msgType, buf);
    }

    if (msgType == QtFatalMsg
            || (msgType == QtWarningMsg
                && (!qgetenv("QT_FATAL_WARNINGS").isNull())) ) {

#if defined(Q_CC_MSVC) && defined(QT_DEBUG) && defined(_DEBUG) && defined(_CRT_ERROR)
        // get the current report mode
        int reportMode = _CrtSetReportMode(_CRT_ERROR, _CRTDBG_MODE_WNDW);
        _CrtSetReportMode(_CRT_ERROR, reportMode);
#if !defined(Q_OS_WINCE)
        int ret = _CrtDbgReport(_CRT_ERROR, __FILE__, __LINE__, QT_VERSION_STR, buf);
#else
        int ret = _CrtDbgReportW(_CRT_ERROR, _CRT_WIDE(__FILE__),
                                 __LINE__, _CRT_WIDE(QT_VERSION_STR),
                                 reinterpret_cast<const wchar_t *> (
                                     QString::fromLatin1(buf).utf16()));
#endif
        if (ret == 0  && reportMode & _CRTDBG_MODE_WNDW)
            return; // ignore
        else if (ret == 1)
            _CrtDbgBreak();
#endif

#if (defined(Q_OS_UNIX) || defined(Q_CC_MINGW))
        abort(); // trap; generates core dump
#else
        exit(1); // goodbye cruel world
#endif
    }
}

void qErrnoWarning(const char *msg, ...)
{
    // qt_error_string() will allocate anyway, so we don't have
    // to be careful here (like we do in plain qWarning())
    QString buf;
    va_list ap;
    va_start(ap, msg);
    if (msg)
        buf.vsprintf(msg, ap);
    va_end(ap);

    QMessageLogger().critical("%s (%s)", buf.toLocal8Bit().constData(),
                              qt_error_string(-1).toLocal8Bit().constData());
}

void qErrnoWarning(int code, const char *msg, ...)
{
    // qt_error_string() will allocate anyway, so we don't have
    // to be careful here (like we do in plain qWarning())
    QString buf;
    va_list ap;
    va_start(ap, msg);
    if (msg)
        buf.vsprintf(msg, ap);
    va_end(ap);

    QMessageLogger().critical("%s (%s)", buf.toLocal8Bit().constData(),
                              qt_error_string(code).toLocal8Bit().constData());
}

#if defined(Q_OS_WIN) && defined(QT_BUILD_CORE_LIB)
extern bool usingWinMain;
extern Q_CORE_EXPORT void qWinMsgHandler(QtMsgType t, const char *str);
extern Q_CORE_EXPORT void qWinMessageHandler(QtMsgType t, const QMessageLogContext &context,
                                             const char *str);
#endif

/*!
    \typedef QtMsgHandler
    \relates <QtGlobal>
    \deprecated

    This is a typedef for a pointer to a function with the following
    signature:

    \snippet doc/src/snippets/code/src_corelib_global_qglobal.cpp 7

    This typedef is deprecated, you should use QMessageHandler instead.
    \sa QtMsgType, QMessageHandler, qInstallMsgHandler(), qInstallMessageHandler()
*/

/*!
    \typedef QMessageHandler
    \relates <QtGlobal>
    \since 5.0

    This is a typedef for a pointer to a function with the following
    signature:

    \snippet doc/src/snippets/code/src_corelib_global_qglobal.cpp 49

    \sa QtMsgType, qInstallMessageHandler()
*/

/*!
    \fn QMessageHandler qInstallMessageHandler(QMessageHandler handler)
    \relates <QtGlobal>
    \since 5.0

    Installs a Qt message \a handler which has been defined
    previously. Returns a pointer to the previous message handler
    (which may be 0).

    The message handler is a function that prints out debug messages,
    warnings, critical and fatal error messages. The Qt library (debug
    mode) contains hundreds of warning messages that are printed
    when internal errors (usually invalid function arguments)
    occur. Qt built in release mode also contains such warnings unless
    QT_NO_WARNING_OUTPUT and/or QT_NO_DEBUG_OUTPUT have been set during
    compilation. If you implement your own message handler, you get total
    control of these messages.

    The default message handler prints the message to the standard
    output under X11 or to the debugger under Windows. If it is a
    fatal message, the application aborts immediately.

    Only one message handler can be defined, since this is usually
    done on an application-wide basis to control debug output.

    To restore the message handler, call \c qInstallMessageHandler(0).

    Example:

    \snippet doc/src/snippets/code/src_corelib_global_qglobal.cpp 23

    \sa qDebug(), qWarning(), qCritical(), qFatal(), QtMsgType,
    {Debugging Techniques}
*/

QMessageHandler qInstallMessageHandler(QMessageHandler h)
{
    if (!messageHandler)
        messageHandler = qDefaultMessageHandler;
    QMessageHandler old = messageHandler;
    messageHandler = h;
#if defined(Q_OS_WIN) && defined(QT_BUILD_CORE_LIB)
    if (!messageHandler && usingWinMain)
        messageHandler = qWinMessageHandler;
#endif
    return old;
}

/*!
    \fn QtMsgHandler qInstallMsgHandler(QtMsgHandler handler)
    \relates <QtGlobal>
    \deprecated

    Installs a Qt message \a handler which has been defined
    previously. This method is deprecated, use qInstallMessageHandler
    instead.
    \sa QtMsgHandler, qInstallMessageHandler
*/

QtMsgHandler qInstallMsgHandler(QtMsgHandler h)
{
    //if handler is 0, set it to the
    //default message handler
    if (!msgHandler)
        msgHandler = qDefaultMsgHandler;
    QtMsgHandler old = msgHandler;
    msgHandler = h;
#if defined(Q_OS_WIN) && defined(QT_BUILD_CORE_LIB)
    if (!msgHandler && usingWinMain)
        msgHandler = qWinMsgHandler;
#endif
    return old;
}

QT_END_NAMESPACE