made wxLogGui more flexible and documented it and added example of customizing it...

[wxWidgets.git] / interface / wx / log.h

/////////////////////////////////////////////////////////////////////////////
// Name:        log.h
// Purpose:     interface of wxLogWindow
// Author:      wxWidgets team
// RCS-ID:      $Id$
// Licence:     wxWindows license
/////////////////////////////////////////////////////////////////////////////

/**
    @class wxLogWindow

    This class represents a background log window: to be precise, it collects all
    log messages in the log frame which it manages but also passes them on to the
    log target which was active at the moment of its creation. This allows you, for
    example, to show all the log messages in a frame but still continue to process
    them normally by showing the standard log dialog.

    @library{wxbase}
    @category{logging}

    @see wxLogTextCtrl
*/
class wxLogWindow : public wxLogInterposer
{
public:
    /**
        Creates the log frame window and starts collecting the messages in it.

        @param parent
            The parent window for the log frame, may be @NULL
        @param title
            The title for the log frame
        @param show
            @true to show the frame initially (default), otherwise
            Show() must be called later.
        @param passToOld
            @true to process the log messages normally in addition to
            logging them in the log frame (default), @false to only log them in the
            log frame.
    */
    wxLogWindow(wxFrame parent, const wxChar title, bool show = true,
                bool passToOld = true);

    /**
        Returns the associated log frame window. This may be used to position or resize
        it but use Show() to show or hide it.
    */
    wxFrame* GetFrame() const;

    /**
        Called if the user closes the window interactively, will not be
        called if it is destroyed for another reason (such as when program
        exits).
        Return @true from here to allow the frame to close, @false to
        prevent this from happening.

        @see OnFrameDelete()
    */
    virtual bool OnFrameClose(wxFrame frame);

    /**
        Called immediately after the log frame creation allowing for
        any extra initializations.
    */
    virtual void OnFrameCreate(wxFrame frame);

    /**
        Called right before the log frame is going to be deleted: will
        always be called unlike OnFrameClose().
    */
    virtual void OnFrameDelete(wxFrame frame);

    /**
        Shows or hides the frame.
    */
    void Show(bool show = true);
};



/**
    @class wxLogInterposerTemp

    A special version of wxLogChain which uses itself as the
    new log target. It forwards log messages to the previously installed one in
    addition to
    processing them itself. Unlike wxLogInterposer, it doesn't
    delete the old target which means it can be used to temporarily redirect log
    output.

    As per wxLogInterposer, this class must be derived from to implement
    wxLog::DoLog
    and/or wxLog::DoLogString methods.

    @library{wxbase}
    @category{logging}
*/
class wxLogInterposerTemp : public wxLogChain
{
public:
    /**
        The default constructor installs this object as the current active log target.
    */
};



/**
    @class wxLogChain

    This simple class allows you to chain log sinks, that is to install a new sink but
    keep passing log messages to the old one instead of replacing it completely as
    wxLog::SetActiveTarget does.

    It is especially useful when you want to divert the logs somewhere (for
    example to a file or a log window) but also keep showing the error messages
    using the standard dialogs as wxLogGui does by default.

    Example of usage:

    @code
    wxLogChain *logChain = new wxLogChain(new wxLogStderr);

    // all the log messages are sent to stderr and also processed as usually
    ...

    // don't delete logChain directly as this would leave a dangling
    // pointer as active log target, use SetActiveTarget() instead
    delete wxLog::SetActiveTarget(...something else or NULL...);
    @endcode

    @library{wxbase}
    @category{logging}
*/
class wxLogChain : public wxLog
{
public:
    /**
        Sets the specified @c logger (which may be @NULL) as the default log
        target but the log messages are also passed to the previous log target if any.
    */
    wxLogChain(wxLog* logger);

    /**
        Destroys the previous log target.
    */
    ~wxLogChain();

    /**
        Detaches the old log target so it won't be destroyed when the wxLogChain object
        is destroyed.
    */
    void DetachOldLog();

    /**
        Returns the pointer to the previously active log target (which may be @NULL).
    */
    wxLog* GetOldLog() const;

    /**
        Returns @true if the messages are passed to the previously active log
        target (default) or @false if PassMessages()
        had been called.
    */
    bool IsPassingMessages() const;

    /**
        By default, the log messages are passed to the previously active log target.
        Calling this function with @false parameter disables this behaviour
        (presumably temporarily, as you shouldn't use wxLogChain at all otherwise) and
        it can be reenabled by calling it again with @a passMessages set to @true.
    */
    void PassMessages(bool passMessages);

    /**
        Sets another log target to use (may be @NULL). The log target specified
        in the wxLogChain(wxLog*) constructor or in a previous call to
        this function is deleted.
        This doesn't change the old log target value (the one the messages are
        forwarded to) which still remains the same as was active when wxLogChain
        object was created.
    */
    void SetLog(wxLog* logger);
};



/**
    @class wxLogGui

    This is the default log target for the GUI wxWidgets applications.

    Please see @ref overview_log_customize for explanation of how to change the
    default log target.

    An object of this class is used by default to show the log messages created
    by using wxLogMessage(), wxLogError() and other logging functions. It
    doesn't display the messages logged by them immediately however but
    accumulates all messages logged during an event handler execution and then
    shows them all at once when its Flush() method is called during the idle
    time processing. This has the important advantage of showing only a single
    dialog to the user even if several messages were logged because of a single
    error as it often happens (e.g. a low level function could log a message
    because it failed to open a file resulting in its caller logging another
    message due to the failure of higher level operation requiring the use of
    this file). If you need to force the display of all previously logged
    messages immediately you can use wxLog::FlushActive() to force the dialog
    display.

    Also notice that if an error message is logged when several informative
    messages had been already logged before, the informative messages are
    discarded on the assumption that they are not useful -- and may be
    confusing and hence harmful -- any more after the error. The warning
    and error messages are never discarded however and any informational
    messages logged after the first error one are also kept (as they may
    contain information about the error recovery). You may override DoLog()
    method to change this behaviour.

    At any rate, it is possible that that several messages were accumulated
    before this class Flush() method is called. If this is the case, Flush()
    uses a custom dialog which shows the last message directly and allows the
    user to view the previously logged ones by expanding the "Details"
    wxCollapsiblePane inside it. This custom dialog also provides the buttons
    for copying the log messages to the clipboard and saving them to a file.

    However if only a single message is present when Flush() is called, just a
    wxMessageBox() is used to show it. This has the advantage of being closer
    to the native behaviour but it doesn't give the user any possibility to
    copy or save the message (except for the recent Windows versions where @c
    Ctrl-C may be pressed in the message box to copy its contents to the
    clipboard) so you may want to override DoShowSingleMessage() to customize
    wxLogGui -- the dialogs sample shows how to do this.

    @library{wxcore}
    @category{logging}
*/
class wxLogGui : public wxLog
{
public:
    /**
        Default constructor.
    */
    wxLogGui();

    /**
        Presents the accumulated log messages, if any, to the user.

        This method is called during the idle time and should show any messages
        accumulated in wxLogGui#m_aMessages field to the user.
     */
    virtual void Flush();

protected:
    /**
        Returns the appropriate title for the dialog.

        The title is constructed from wxApp::GetAppDisplayName() and the
        severity string (e.g. "error" or "warning") appropriate for the current
        wxLogGui#m_bErrors and wxLogGui#m_bWarnings values.
     */
    wxString GetTitle() const;

    /**
        Returns wxICON_ERROR, wxICON_WARNING or wxICON_INFORMATION depending on
        the current maximal severity.

        This value is suitable to be used in the style parameter of
        wxMessageBox() function.
     */
    int GetSeverityIcon() const;

    /**
        Forgets all the currently stored messages.

        If you override Flush() (and don't call the base class version), you
        must call this method to avoid messages being logged over and over
        again.
     */
    void Clear();


    /**
        Method called by Flush() to show a single log message.

        This function can be overridden to show the message in a different way.
        By default a simple wxMessageBox() call is used.

        @param message
            The message to show (it can contain multiple lines).
        @param title
            The suggested title for the dialog showing the message, see
            GetTitle().
        @param style
            One of @c wxICON_XXX constants, see GetSeverityIcon().
     */
    virtual void DoShowSingleLogMessage(const wxString& message,
                                        const wxString& title,
                                        int style);

    /**
        Method called by Flush() to show multiple log messages.

        This function can be overridden to show the messages in a different way.
        By default a special log dialog showing the most recent message and
        allowing the user to expand it to view the previously logged ones is
        used.

        @param messages
            Array of messages to show; it contains more than one element.
        @param severities
            Array of message severities containing @c wxLOG_XXX values.
        @param times
            Array of time_t values indicating when each message was logged.
        @param title
            The suggested title for the dialog showing the message, see
            GetTitle().
        @param style
            One of @c wxICON_XXX constants, see GetSeverityIcon().
     */
    virtual void DoShowMultipleLogMessages(const wxArrayString& messages,
                                           const wxArrayInt& severities,
                                           const wxArrayLong& times,
                                           const wxString& title,
                                           int style);


    /**
        All currently accumulated messages.

        This array may be empty if no messages were logged.

        @see m_aSeverity, m_aTimes
     */
    wxArrayString m_aMessages;

    /**
        The severities of each logged message.

        This array is synchronized with wxLogGui#m_aMessages, i.e. the n-th
        element of this array corresponds to the severity of the n-th message.
        The possible severity values are @c wxLOG_XXX constants, e.g.
        wxLOG_Error, wxLOG_Warning, wxLOG_Message etc.
     */
    wxArrayInt m_aSeverity;

    /**
        The time stamps of each logged message.

        The elements of this array are time_t values corresponding to the time
        when the message was logged.
     */
    wxArrayLong m_aTimes;

    /**
        True if there any error messages.
     */
    bool m_bErrors;

    /**
        True if there any warning messages.

        If both wxLogGui#m_bErrors and this member are false, there are only
        informational messages to be shown.
     */
    bool m_bWarnings;

    /**
        True if there any messages to be shown to the user.

        This variable is used instead of simply checking whether
        wxLogGui#m_aMessages array is empty to allow blocking further calls to
        Flush() while a log dialog is already being shown, even if the messages
        array hasn't been emptied yet.
     */
    bool m_bHasMessages;
};



/**
    @class wxLogStream

    This class can be used to redirect the log messages to a C++ stream.

    Please note that this class is only available if wxWidgets was compiled with
    the standard iostream library support (@c wxUSE_STD_IOSTREAM must be on).

    @library{wxbase}
    @category{logging}

    @see wxLogStderr, wxStreamToTextRedirector
*/
class wxLogStream : public wxLog
{
public:
    /**
        Constructs a log target which sends all the log messages to the given
        output stream. If it is @NULL, the messages are sent to @c cerr.
    */
    wxLogStream(std::ostream ostr = NULL);
};



/**
    @class wxLogStderr

    This class can be used to redirect the log messages to a C file stream (not to
    be confused with C++ streams). It is the default log target for the non-GUI
    wxWidgets applications which send all the output to @c stderr.

    @library{wxbase}
    @category{logging}

    @see wxLogStream
*/
class wxLogStderr : public wxLog
{
public:
    /**
        Constructs a log target which sends all the log messages to the given
        @c FILE. If it is @NULL, the messages are sent to @c stderr.
    */
    wxLogStderr(FILE fp = NULL);
};



/**
    @class wxLogBuffer

    wxLogBuffer is a very simple implementation of log sink which simply collects
    all the logged messages in a string (except the debug messages which are output
    in the usual way immediately as we're presumably not interested in collecting
    them for later). The messages from different log function calls are separated
    by the new lines.

    All the messages collected so far can be shown to the user (and the current
    buffer cleared) by calling the overloaded wxLogBuffer::Flush
    method.

    @library{wxbase}
    @category{logging}
*/
class wxLogBuffer : public wxLog
{
public:
    /**
        Shows all the messages collected so far to the user (using a message box in the
        GUI applications or by printing them out to the console in text mode) and
        clears the internal buffer.
    */
    virtual void Flush();

    /**
        Returns the current buffer contains. Messages from different log function calls
        are separated with the new lines in the buffer.
        The buffer can be cleared by Flush() which will
        also show the current contents to the user.
    */
    const wxString GetBuffer();
};



/**
    @class wxLogInterposer

    A special version of wxLogChain which uses itself as the
    new log target. It forwards log messages to the previously installed one in
    addition to
    processing them itself.

    Unlike wxLogChain which is usually used directly as is,
    this class must be derived from to implement wxLog::DoLog
    and/or wxLog::DoLogString methods.

    wxLogInterposer destroys the previous log target in its destructor. If you
    don't want this to happen, use wxLogInterposerTemp instead.

    @library{wxbase}
    @category{logging}
*/
class wxLogInterposer : public wxLogChain
{
public:
    /**
        The default constructor installs this object as the current active log target.
    */
};



/**
    @class wxLogTextCtrl

    Using these target all the log messages can be redirected to a text control.
    The text control must have been created with @c wxTE_MULTILINE style by the
    caller previously.

    @library{wxbase}
    @category{logging}

    @see wxTextCtrl, wxStreamToTextRedirector
*/
class wxLogTextCtrl : public wxLog
{
public:
    /**
        Constructs a log target which sends all the log messages to the given text
        control. The @a textctrl parameter cannot be @NULL.
    */
    wxLogTextCtrl(wxTextCtrl textctrl);
};



/**
    @class wxLog

    wxLog class defines the interface for the @e log targets used by wxWidgets
    logging functions as explained in the @ref overview_log.
    The only situations when you need to directly use this class is when you want
    to derive your own log target because the existing ones don't satisfy your
    needs. Another case is if you wish to customize the behaviour of the standard
    logging classes (all of which respect the wxLog settings): for example, set
    which trace messages are logged and which are not or change (or even remove
    completely) the timestamp on the messages.

    Otherwise, it is completely hidden behind the @e wxLogXXX() functions and
    you may not even know about its existence.

     @section overview_wxLog_deriving Deriving your own log target
     
        There are two functions which must be implemented by any derived class to
        actually process the log messages: DoLog() and
        DoLogString(). The second function receives a string
        which just has to be output in some way and the easiest way to write a new log
        target is to override just this function in the derived class. If more control
        over the output format is needed, then the first function must be overridden
        which allows to construct custom messages depending on the log level or even
        do completely different things depending on the message severity (for example,
        throw away all messages except warnings and errors, show warnings on the
        screen and forward the error messages to the user's (or programmer's) cell
        phone - maybe depending on whether the timestamp tells us if it is day or
        night in the current time zone).
        There also functions to support message buffering. Why are they needed?
        Some of wxLog implementations, most notably the standard wxLogGui class,
        buffer the messages (for example, to avoid showing the user a zillion of modal
        message boxes one after another -- which would be really annoying).
        Flush() shows them all and clears the buffer contents.
        This function doesn't do anything if the buffer is already empty.
        See also:
        @li Flush()
        @li FlushActive()

     @section overview_wxLog_Trace_Masks Using trace masks

        The functions below allow some limited customization of wxLog behaviour
        without writing a new log target class (which, aside from being a matter of
        several minutes, allows you to do anything you want).
        The verbose messages are the trace messages which are not disabled in the
        release mode and are generated by wxLogVerbose(). They
        are not normally shown to the user because they present little interest, but
        may be activated, for example, in order to help the user find some program
        problem.
        As for the (real) trace messages, their handling depends on the settings of
        the (application global) @e trace mask which can either be specified using
        SetTraceMask(), GetTraceMask() and wxLogTrace() which takes an integer mask
        or using AddTraceMask() for string trace masks.
        The difference between bit-wise and string trace masks is that a message using
        integer trace mask will only be logged if all bits of the mask are set in the
        current mask while a message using string mask will be logged simply if the
        mask had been added before to the list of allowed ones.
        For example,
        
        @code
        wxLogTrace( wxTraceRefCount|wxTraceOleCalls, "Active object ref count: %d", nRef );
        @endcode

        will do something only if the current trace mask contains both
        @c wxTraceRefCount and @c wxTraceOle, but

        @code
        wxLogTrace( wxTRACE_OleCalls, "IFoo::Bar() called" );
        @endcode
        
        will log the message if it was preceded by
        
        @code
        wxLog::AddTraceMask( wxTRACE_OleCalls);
        @endcode

        Using string masks is simpler and allows you to easily add custom ones, so this is
        the preferred way of working with trace messages. The integer trace mask is
        kept for compatibility and for additional (but very rarely needed) flexibility
        only.
        The standard trace masks are given in wxLogTrace() documentation.
        Finally, the @e wxLog::DoLog() function automatically prepends a time stamp
        to all the messages. The format of the time stamp may be changed: it can be
        any string with % specifications fully described in the documentation of the
        standard @e strftime() function. For example, the default format is
        "[%d/%b/%y %H:%M:%S] " which gives something like "[17/Sep/98 22:10:16] "
        (without quotes) for the current date. Setting an empty string as the time
        format disables timestamping of the messages completely.
        See also
        @li AddTraceMask()
        @li RemoveTraceMask()
        @li ClearTraceMasks()
        @li GetTraceMasks()
        @li IsAllowedTraceMask()
        @li SetVerbose()
        @li GetVerbose()
        @li SetTimestamp()
        @li GetTimestamp()
        @li SetTraceMask()
        @li GetTraceMask()
        @li SetRepetitionCounting()
        @li GetRepetitionCounting()

        @note Timestamping is disabled for Visual C++ users in debug builds by
        default because otherwise it would be impossible to directly go to the line
        from which the log message was generated by simply clicking in the debugger
        window on the corresponding error message. If you wish to enable it, please
        use SetTimestamp() explicitly. 
        
     @section overview_wxLog_Target Manipulating the log target

        The functions in this section work with and manipulate the active log
        target. The OnLog() is called by the @e wxLogXXX() functions
        and invokes the DoLog() of the active log target if any.
        Get/Set methods are used to install/query the current active target and,
        finally, DontCreateOnDemand() disables the automatic creation of a standard
        log target if none actually exists. It is only useful when the application
        is terminating and shouldn't be used in other situations because it may
        easily lead to a loss of messages. See also
        @li OnLog()
        @li GetActiveTarget()
        @li SetActiveTarget()
        @li DontCreateOnDemand()
        @li Suspend()
        @li Resume()

    @library{wxcore}
    @category{logging}

    @see @ref overview_log
*/
class wxLog
{
public:
    /**
        Add the @a mask to the list of allowed masks for
        wxLogTrace().

        @see RemoveTraceMask(), GetTraceMasks()
    */
    static void AddTraceMask(const wxString& mask);

    /**
        Removes all trace masks previously set with
        AddTraceMask().

        @see RemoveTraceMask()
    */
    static void ClearTraceMasks();

    /**
        Disables time stamping of the log messages.
        This function is new since wxWidgets version 2.9
    */
    void SetTimestamp(const wxString& format);

    /**
        Called to process the message of the specified severity. @a msg is the text
        of the message as specified in the call of @e wxLogXXX() function which
        generated it and @a timestamp is the moment when the message was generated.
        The base class version prepends the timestamp to the message, adds a prefix
        corresponding to the log level and then calls
        DoLogString() with the resulting string.
    */
    virtual void DoLog(wxLogLevel level, const wxString& msg,
                       time_t timestamp);

    /**
        Called to log the specified string. The timestamp is already included in the
        string but still passed to this function.
        A simple implementation may just send the string to @c stdout or, better,
        @c stderr.
    */
    virtual void DoLogString(const wxString& msg, time_t timestamp);

    /**
        Instructs wxLog to not create new log targets on the fly if there is none
        currently. (Almost) for internal use only: it is supposed to be called by the
        application shutdown code.
        Note that this function also calls
        ClearTraceMasks().
    */
    static void DontCreateOnDemand();

    /**
        Shows all the messages currently in buffer and clears it. If the buffer
        is already empty, nothing happens.
    */
    virtual void Flush();

    /**
        Flushes the current log target if any, does nothing if there is none.

        @see Flush()
    */
    static void FlushActive();

    /**
        Returns the pointer to the active log target (may be @NULL).
    */
    static wxLog* GetActiveTarget();

    /**
        Returns the current log level limit.
    */
    static wxLogLevel GetLogLevel();

    /**
        Returns whether the repetition counting mode is enabled.
    */
    static bool GetRepetitionCounting();

    /**
        Returns the current timestamp format string.
    */
    static const wxString GetTimestamp();

    /**
        Returns the current trace mask, see Customization() section
        for details.
    */
    static wxTraceMask GetTraceMask();

    /**
        Returns the currently allowed list of string trace masks.

        @see AddTraceMask().
    */
    static const wxArrayString GetTraceMasks();

    /**
        Returns whether the verbose mode is currently active.
    */
    static bool GetVerbose();

    /**
        Returns @true if the @a mask is one of allowed masks for
        wxLogTrace().
        
        See also: AddTraceMask(), RemoveTraceMask()
    */
    static bool IsAllowedTraceMask(const wxString& mask);

    /**
        There are two functions which must be implemented by any derived class to
        actually process the log messages: DoLog() and
        DoLogString(). The second function receives a string
        which just has to be output in some way and the easiest way to write a new log
        target is to override just this function in the derived class. If more control
        over the output format is needed, then the first function must be overridden
        which allows you to construct custom messages depending on the log level or even
        do completely different things depending on the message severity (for example,
        throw away all messages except warnings and errors, show warnings on the
        screen and forward the error messages to the user's (or programmer's) cell
        phone - maybe depending on whether the timestamp tells us if it is day or
        night in the current time zone).
        There also functions to support message buffering. Why are they needed?
        Some of wxLog implementations, most notably the standard wxLogGui class,
        buffer the messages (for example, to avoid showing the user a zillion of modal
        message boxes one after another -- which would be really annoying).
        Flush() shows them all and clears the buffer contents.
        This function doesn't do anything if the buffer is already empty.
        Flush()

        FlushActive()
    */


    /**
        Forwards the message at specified level to the @e DoLog() function of the
        active log target if there is any, does nothing otherwise.
    */
    static void OnLog(wxLogLevel level, const wxString& message);

    /**
        Remove the @a mask from the list of allowed masks for
        wxLogTrace().
        See also: AddTraceMask()
    */
    static void RemoveTraceMask(const wxString& mask);

    /**
        Resumes logging previously suspended by a call to Suspend().
        All messages logged in the meanwhile will be flushed soon.
    */
    static void Resume();

    /**
        Sets the specified log target as the active one.

        Returns the pointer to the previous active log target (may be @NULL).
        To suppress logging use a new instance of wxLogNull not @NULL.  If the
        active log target is set to @NULL a new default log target will be
        created when logging occurs.
    */
    static wxLog* SetActiveTarget(wxLog* logtarget);

    /**
        Specifies that log messages with level  logLevel should be ignored
        and not sent to the active log target.
    */
    static void SetLogLevel(wxLogLevel logLevel);

    /**
        Enables logging mode in which a log message is logged once, and in case exactly
        the same message successively repeats one or more times, only the number of
        repetitions is logged.
    */
    static void SetRepetitionCounting(bool repetCounting = true);

    /**
        Sets the timestamp format prepended by the default log targets to all
        messages. The string may contain any normal characters as well as %
        prefixed format specificators, see @e strftime() manual for details.
        Passing an empty string to this function disables message time stamping.
    */
    static void SetTimestamp(const wxString& format);

    /**
        Sets the trace mask, see Customization()
        section for details.
    */
    static void SetTraceMask(wxTraceMask mask);

    /**
        Activates or deactivates verbose mode in which the verbose messages are
        logged as the normal ones instead of being silently dropped.
    */
    static void SetVerbose(bool verbose = true);

    /**
        Suspends the logging until Resume() is called. Note that
        the latter must be called the same number of times as the former to undo it,
        i.e. if you call Suspend() twice you must call Resume() twice as well.
        Note that suspending the logging means that the log sink won't be be flushed
        periodically, it doesn't have any effect if the current log target does the
        logging immediately without waiting for Flush() to be
        called (the standard GUI log target only shows the log dialog when it is
        flushed, so Suspend() works as expected with it).

        @see Resume(), wxLogNull
    */
    static void Suspend();
};



/**
    @class wxLogNull

    This class allows you to temporarily suspend logging. All calls to the log
    functions during the life time of an object of this class are just ignored.

    In particular, it can be used to suppress the log messages given by wxWidgets
    itself but it should be noted that it is rarely the best way to cope with this
    problem as @b all log messages are suppressed, even if they indicate a
    completely different error than the one the programmer wanted to suppress.

    For instance, the example of the overview:

    @code
    wxFile file;

      // wxFile.Open() normally complains if file can't be opened, we don't want it
      {
        wxLogNull logNo;
        if ( !file.Open("bar") )
          ... process error ourselves ...
      } // ~wxLogNull called, old log sink restored

      wxLogMessage("..."); // ok
    @endcode

    would be better written as:

    @code
    wxFile file;

      // don't try to open file if it doesn't exist, we are prepared to deal with
      // this ourselves - but all other errors are not expected
      if ( wxFile::Exists("bar") )
      {
          // gives an error message if the file couldn't be opened
          file.Open("bar");
      }
      else
      {
          ...
      }
    @endcode


    @library{wxbase}
    @category{logging}
*/
class wxLogNull : public wxLog
{
public:
    /**
        Suspends logging.
    */
    wxLogNull();

    /**
        Resumes logging.
    */
};



// ============================================================================
// Global functions/macros
// ============================================================================

/** @ingroup group_funcmacro_log */
//@{

/**
    This function shows a message to the user in a safe way and should be safe
    to call even before the application has been initialized or if it is
    currently in some other strange state (for example, about to crash). Under
    Windows this function shows a message box using a native dialog instead of
    wxMessageBox() (which might be unsafe to call), elsewhere it simply prints
    the message to the standard output using the title as prefix.

    @param title
        The title of the message box shown to the user or the prefix of the
        message string.
    @param text
        The text to show to the user.

    @see wxLogFatalError()

    @header{wx/log.h}
*/
void wxSafeShowMessage(const wxString& title, const wxString& text);

/**
    Returns the error code from the last system call. This function uses
    @c errno on Unix platforms and @c GetLastError under Win32.

    @see wxSysErrorMsg(), wxLogSysError()

    @header{wx/log.h}
*/
unsigned long wxSysErrorCode();

/**
    Returns the error message corresponding to the given system error code. If
    @a errCode is 0 (default), the last error code (as returned by
    wxSysErrorCode()) is used.

    @see wxSysErrorCode(), wxLogSysError()

    @header{wx/log.h}
*/
const wxChar* wxSysErrorMsg(unsigned long errCode = 0);

//@}

/** @ingroup group_funcmacro_log */
//@{
/**
    For all normal, informational messages. They also appear in a message box
    by default (but it can be changed).

    @header{wx/log.h}
*/
void wxLogMessage(const char* formatString, ... );
void wxVLogMessage(const char* formatString, va_list argPtr);
//@}

/** @ingroup group_funcmacro_log */
//@{
/**
    For verbose output. Normally, it is suppressed, but might be activated if
    the user wishes to know more details about the program progress (another,
    but possibly confusing name for the same function could be @c wxLogInfo).

    @header{wx/log.h}
*/
void wxLogVerbose(const char* formatString, ... );
void wxVLogVerbose(const char* formatString, va_list argPtr);
//@}

/** @ingroup group_funcmacro_log */
//@{
/**
    For warnings - they are also normally shown to the user, but don't
    interrupt the program work.

    @header{wx/log.h}
*/
void wxLogWarning(const char* formatString, ... );
void wxVLogWarning(const char* formatString, va_list argPtr);
//@}

/** @ingroup group_funcmacro_log */
//@{
/**
    Like wxLogError(), but also terminates the program with the exit code 3.
    Using @e abort() standard function also terminates the program with this
    exit code.

    @header{wx/log.h}
*/
void wxLogFatalError(const char* formatString, ... );
void wxVLogFatalError(const char* formatString, va_list argPtr);
//@}

/** @ingroup group_funcmacro_log */
//@{
/**
    The functions to use for error messages, i.e. the messages that must be
    shown to the user. The default processing is to pop up a message box to
    inform the user about it.

    @header{wx/log.h}
*/
void wxLogError(const char* formatString, ... );
void wxVLogError(const char* formatString, va_list argPtr);
//@}

/** @ingroup group_funcmacro_log */
//@{
/**
    Like wxLogDebug(), trace functions only do something in debug builds and
    expand to nothing in the release one. The reason for making it a separate
    function is that usually there are a lot of trace messages, so it might
    make sense to separate them from other debug messages.

    wxLogDebug(const char*,const char*,...) and
    wxLogDebug(wxTraceMask,const char*,...) can be used instead if you would
    like to be able to separate trace messages into different categories which
    can be enabled or disabled with the static functions provided in wxLog.

    @header{wx/log.h}
*/
void wxLogTrace(const char* formatString, ... );
void wxVLogTrace(const char* formatString, va_list argPtr);
//@}

/** @ingroup group_funcmacro_log */
//@{
/**
    Like wxLogDebug(), trace functions only do something in debug builds and
    expand to nothing in the release one. The reason for making it a separate
    function is that usually there are a lot of trace messages, so it might
    make sense to separate them from other debug messages.

    In this version of wxLogTrace(), trace messages can be separated into
    different categories and calls using this function only log the message if
    the given @a mask is currently enabled in wxLog. This lets you selectively
    trace only some operations and not others by enabling the desired trace
    masks with wxLog::AddTraceMask() or by setting the
    @ref overview_envvars "@c WXTRACE environment variable".

    The predefined string trace masks used by wxWidgets are:

    @beginDefList
    @itemdef{ wxTRACE_MemAlloc, Trace memory allocation (new/delete) }
    @itemdef{ wxTRACE_Messages, Trace window messages/X callbacks }
    @itemdef{ wxTRACE_ResAlloc, Trace GDI resource allocation }
    @itemdef{ wxTRACE_RefCount, Trace various ref counting operations }
    @itemdef{ wxTRACE_OleCalls, Trace OLE method calls (Win32 only) }
    @endDefList

    @note Since both the mask and the format string are strings, this might
          lead to function signature confusion in some cases: if you intend to
          call the format string only version of wxLogTrace(), add a "%s"
          format string parameter and then supply a second string parameter for
          that "%s", the string mask version of wxLogTrace() will erroneously
          get called instead, since you are supplying two string parameters to
          the function. In this case you'll unfortunately have to avoid having
          two leading string parameters, e.g. by adding a bogus integer (with
          its "%d" format string).

    @header{wx/log.h}
*/
void wxLogTrace(const char* mask, const char* formatString, ... );
void wxVLogTrace(const char* mask,
                  const char* formatString,
                  va_list argPtr);
//@}

/** @ingroup group_funcmacro_log */
//@{
/**
    Like wxLogDebug(), trace functions only do something in debug builds and
    expand to nothing in the release one. The reason for making it a separate
    function is that usually there are a lot of trace messages, so it might
    make sense to separate them from other debug messages.

    This version of wxLogTrace() only logs the message if all the bits
    corresponding to the @a mask are set in the wxLog trace mask which can be
    set by calling wxLog::SetTraceMask(). This version is less flexible than
    wxLogDebug(const char*,const char*,...) because it doesn't allow defining
    the user trace masks easily. This is why it is deprecated in favour of
    using string trace masks.

    The following bitmasks are defined for wxTraceMask:

    @beginDefList
    @itemdef{ wxTraceMemAlloc, Trace memory allocation (new/delete) }
    @itemdef{ wxTraceMessages, Trace window messages/X callbacks }
    @itemdef{ wxTraceResAlloc, Trace GDI resource allocation }
    @itemdef{ wxTraceRefCount, Trace various ref counting operations }
    @itemdef{ wxTraceOleCalls, Trace OLE method calls (Win32 only) }
    @endDefList

    @header{wx/log.h}
*/
void wxLogTrace(wxTraceMask mask, const char* formatString, ... );
void wxVLogTrace(wxTraceMask mask, const char* formatString, va_list argPtr);
//@}

/** @ingroup group_funcmacro_log */
//@{
/**
    The right functions for debug output. They only do something in debug mode
    (when the preprocessor symbol @c __WXDEBUG__ is defined) and expand to
    nothing in release mode (otherwise).

    @header{wx/log.h}
*/
void wxLogDebug(const char* formatString, ... );
void wxVLogDebug(const char* formatString, va_list argPtr);
//@}

/** @ingroup group_funcmacro_log */
//@{
/**
    Messages logged by this function will appear in the statusbar of the
    @a frame or of the top level application window by default (i.e. when using
    the second version of the functions).

    If the target frame doesn't have a statusbar, the message will be lost.

    @header{wx/log.h}
*/
void wxLogStatus(wxFrame* frame, const char* formatString, ... );
void wxVLogStatus(wxFrame* frame, const char* formatString, va_list argPtr);
void wxLogStatus(const char* formatString, ... );
void wxVLogStatus(const char* formatString, va_list argPtr);
//@}

/** @ingroup group_funcmacro_log */
//@{
/**
    Mostly used by wxWidgets itself, but might be handy for logging errors
    after system call (API function) failure. It logs the specified message
    text as well as the last system error code (@e errno or @e ::GetLastError()
    depending on the platform) and the corresponding error message. The second
    form of this function takes the error code explicitly as the first
    argument.

    @see wxSysErrorCode(), wxSysErrorMsg()

    @header{wx/log.h}
*/
void wxLogSysError(const char* formatString, ... );
void wxVLogSysError(const char* formatString, va_list argPtr);
//@}