- @page log_overview wxLog classes overview
-
- Classes: #wxLog,
-
- #wxLogStderr,
-
- #wxLogStream,
-
- #wxLogTextCtrl,
-
- #wxLogWindow,
-
- #wxLogGui,
-
- #wxLogNull,
-
- #wxLogBuffer,
-
- #wxLogChain,
-
- #wxLogInterposer,
-
- #wxLogInterposerTemp,
-
- #wxStreamToTextRedirector
- This is a general overview of logging classes provided by wxWidgets. The word
- logging here has a broad sense, including all of the program output, not only
- non-interactive messages. The logging facilities included in wxWidgets provide
- the base @e wxLog class which defines the standard interface for a @e log
- target as well as several standard implementations of it and a family of
- functions to use with them.
- First of all, no knowledge of @e wxLog classes is needed to use them. For
- this, you should only know about @e wxLogXXX() functions. All of them have
- the same syntax as @e printf() or @e vprintf() , i.e. they take the
- format string as the first argument and respectively a variable number of
- arguments or a variable argument list pointer. Here are all of them:
-
-
- @b wxLogFatalError which is like @e wxLogError, but also
- terminates the program with the exit code 3 (using @e abort() standard
- function). Unlike for all the other logging functions, this function can't be
- overridden by a log target.
- @b wxLogError is the function 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.
- @b wxLogWarning for warnings - they are also normally shown to the
- user, but don't interrupt the program work.
- @b wxLogMessage is for all normal, informational messages. They also
- appear in a message box by default (but it can be changed, see below).
- @b wxLogVerbose is 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 is @b wxLogInfo).
- @b wxLogStatus is for status messages - they will go into the status
- bar of the active or specified (as the first argument) #wxFrame if it has one.
- @b wxLogSysError is 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.
- @b wxLogDebug is @b the right function for debug output. It only
- does anything at all in the debug mode (when the preprocessor symbol
- __WXDEBUG__ is defined) and expands to nothing in release mode (otherwise).
- @b Tip: under Windows, you must either run the program under debugger or
- use a 3rd party program such as #DbgView
- to actually see the debug output.
- @b wxLogTrace as @b wxLogDebug only does something in debug
- build. The reason for making it a separate function from it is that usually
- there are a lot of trace messages, so it might make sense to separate them
- from other debug messages which would be flooded in them. Moreover, the second
- version of this function takes a trace mask as the first argument which allows
- to further restrict the amount of messages generated.
-
-
- The usage of these functions should be fairly straightforward, however it may
- be asked why not use the other logging facilities, such as C standard stdio
- functions or C++ streams. The short answer is that they're all very good
- generic mechanisms, but are not really adapted for wxWidgets, while the log
- classes are. Some of advantages in using wxWidgets log functions are:
-
-
- @b Portability It is a common practice to use @e printf()
- statements or cout/cerr C++ streams for writing out some (debug or otherwise)
- information.
- Although it works just fine under Unix, these messages go strictly nowhere
- under Windows where the stdout of GUI programs is not assigned to anything.
- Thus, you might view @e wxLogMessage() as a simple substitute for @e printf().
- You can also redirect the @e wxLogXXX calls to @e cout by just writing:
-
-
- @code
- wxLog *logger=new wxLogStream();
- wxLog::SetActiveTarget(logger);
- @endcode
-
-
- Finally, there is also a possibility to redirect the output sent to @e cout
- to a #wxTextCtrl by using the
- #wxStreamToTextRedirector class.
- @b Flexibility The output of wxLog functions can be redirected or
- suppressed entirely based on their importance, which is either impossible or
- difficult to do with traditional methods. For example, only error messages, or
- only error messages and warnings might be logged, filtering out all
- informational messages.
- @b Completeness Usually, an error message should be presented to the user
- when some operation fails. Let's take a quite simple but common case of a file
- error: suppose that you're writing your data file on disk and there is not
- enough space. The actual error might have been detected inside wxWidgets code
- (say, in @e wxFile::Write), so the calling function doesn't really know the
- exact reason of the failure, it only knows that the data file couldn't be
- written to the disk. However, as wxWidgets uses @e wxLogError() in this
- situation, the exact error code (and the corresponding error message) will be
- given to the user together with "high level" message about data file writing
- error.
-
-
- After having enumerated all the functions which are normally used to log the
- messages, and why would you want to use them we now describe how all this
- works.
- wxWidgets has the notion of a @e log target: it is just a class deriving
- from #wxLog. As such, it implements the virtual functions of
- the base class which are called when a message is logged. Only one log target
- is @e active at any moment, this is the one used by @e wxLogXXX()
- functions. The normal usage of a log object (i.e. object of a class derived
- from wxLog) is to install it as the active target with a call to @e SetActiveTarget() and it will be used automatically by all subsequent calls
- to @e wxLogXXX() functions.
- To create a new log target class you only need to derive it from wxLog and
- implement one (or both) of @e DoLog() and @e DoLogString() in it. The
- second one is enough if you're happy with the standard wxLog message
- formatting (prepending "Error:" or "Warning:", timestamping c) but just want
- to send the messages somewhere else. The first one may be overridden to do
- whatever you want but you have to distinguish between the different message
- types yourself.
- There are some predefined classes deriving from wxLog and which might be
- helpful to see how you can create a new log target class and, of course, may
- also be used without any change. There are:
-
-
- @b wxLogStderr This class logs messages to a @e FILE *, using
- stderr by default as its name suggests.
- @b wxLogStream This class has the same functionality as wxLogStderr,
- but uses @e ostream and cerr instead of @e FILE * and stderr.
- @b wxLogGui This is the standard log target for wxWidgets
- applications (it is used by default if you don't do anything) and provides the
- most reasonable handling of all types of messages for given platform.
- @b wxLogWindow This log target provides a "log console" which
- collects all messages generated by the application and also passes them to the
- previous active log target. The log window frame has a menu allowing user to
- clear the log, close it completely or save all messages to file.
- @b wxLogBuffer This target collects all the logged messages in an
- internal buffer allowing to show them later to the user all at once.
- @b wxLogNull The last log class is quite particular: it doesn't do
- anything. The objects of this class may be instantiated to (temporarily)
- suppress output of @e wxLogXXX() functions. As an example, trying to open a
- non-existing file will usually provoke an error message, but if for some
- reasons it is unwanted, just use this construction:
-
- @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
-
-
-
- The log targets can also be combined: for example you may wish to redirect the
- messages somewhere else (for example, to a log file) but also process them as
- normally. For this the #wxLogChain, #wxLogInterposer and
- #wxLogInterposerTemp can be used.
-
- */
-
+@page overview_log wxLog Classes Overview
+
+Classes:
+@li wxLog
+@li wxLogStderr
+@li wxLogStream
+@li wxLogTextCtrl
+@li wxLogWindow
+@li wxLogGui
+@li wxLogNull
+@li wxLogBuffer
+@li wxLogChain
+@li wxLogInterposer
+@li wxLogInterposerTemp
+@li wxStreamToTextRedirector
+
+This is a general overview of logging classes provided by wxWidgets. The word
+logging here has a broad sense, including all of the program output, not only
+non-interactive messages. The logging facilities included in wxWidgets provide
+the base wxLog class which defines the standard interface for a @e log target
+as well as several standard implementations of it and a family of functions to
+use with them.
+
+First of all, no knowledge of wxLog classes is needed to use them. For this,
+you should only know about @e wxLogXXX() functions. All of them have the same
+syntax as @e printf() or @e vprintf() , i.e. they take the format string as the
+first argument and respectively a variable number of arguments or a variable
+argument list pointer. Here are all of them:
+
+@li wxLogFatalError which is like wxLogError, but also terminates the program
+ with the exit code 3 (using @e abort() standard function). Unlike for all
+ the other logging functions, this function can't be overridden by a log
+ target.
+@li wxLogError is the function 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.
+@li wxLogWarning for warnings. They are also normally shown to the user, but
+ don't interrupt the program work.
+@li wxLogMessage is for all normal, informational messages. They also appear in
+ a message box by default (but it can be changed, see below).
+@li wxLogVerbose is 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 is
+ wxLogInfo).
+@li wxLogStatus is for status messages. They will go into the status bar of the
+ active or specified (as the first argument) wxFrame if it has one.
+@li wxLogSysError is 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
+ ::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.
+@li wxLogDebug is @b the right function for debug output. It only does anything
+ at all in the debug mode (when the preprocessor symbol __WXDEBUG__ is
+ defined) and expands to nothing in release mode (otherwise). @b Tip: under
+ Windows, you must either run the program under debugger or use a 3rd party
+ program such as DebugView to actually see the debug output.
+ - DebugView: http://www.microsoft.com/technet/sysinternals/Miscellaneous/DebugView.mspx
+@li wxLogTrace as wxLogDebug only does something in debug build. The reason for
+ making it a separate function from it is that usually there are a lot of
+ trace messages, so it might make sense to separate them from other debug
+ messages which would be flooded in them. Moreover, the second version of
+ this function takes a trace mask as the first argument which allows to
+ further restrict the amount of messages generated.
+
+The usage of these functions should be fairly straightforward, however it may
+be asked why not use the other logging facilities, such as C standard stdio
+functions or C++ streams. The short answer is that they're all very good
+generic mechanisms, but are not really adapted for wxWidgets, while the log
+classes are. Some of advantages in using wxWidgets log functions are:
+
+@li @b Portability: It is a common practice to use @e printf() statements or
+ cout/cerr C++ streams for writing out some (debug or otherwise)
+ information. Although it works just fine under Unix, these messages go
+ strictly nowhere under Windows where the stdout of GUI programs is not
+ assigned to anything. Thus, you might view wxLogMessage() as a simple
+ substitute for @e printf().
+ You can also redirect the @e wxLogXXX calls to @e cout by just writing:
+ @code
+ wxLog* logger = new wxLogStream(&cout);
+ wxLog::SetActiveTarget(logger);
+ @endcode
+ Finally, there is also a possibility to redirect the output sent to @e cout
+ to a wxTextCtrl by using the wxStreamToTextRedirector class.
+@li @b Flexibility: The output of wxLog functions can be redirected or
+ suppressed entirely based on their importance, which is either impossible
+ or difficult to do with traditional methods. For example, only error
+ messages, or only error messages and warnings might be logged, filtering
+ out all informational messages.
+@li @b Completeness: Usually, an error message should be presented to the user
+ when some operation fails. Let's take a quite simple but common case of a
+ file error: suppose that you're writing your data file on disk and there is
+ not enough space. The actual error might have been detected inside
+ wxWidgets code (say, in wxFile::Write), so the calling function doesn't
+ really know the exact reason of the failure, it only knows that the data
+ file couldn't be written to the disk. However, as wxWidgets uses
+ wxLogError() in this situation, the exact error code (and the corresponding
+ error message) will be given to the user together with "high level" message
+ about data file writing error.
+
+After having enumerated all the functions which are normally used to log the
+messages, and why would you want to use them we now describe how all this
+works.
+
+wxWidgets has the notion of a <em>log target</em>: it is just a class deriving
+from wxLog. As such, it implements the virtual functions of the base class
+which are called when a message is logged. Only one log target is @e active at
+any moment, this is the one used by @e wxLogXXX() functions. The normal usage
+of a log object (i.e. object of a class derived from wxLog) is to install it as
+the active target with a call to @e SetActiveTarget() and it will be used
+automatically by all subsequent calls to @e wxLogXXX() functions.
+
+To create a new log target class you only need to derive it from wxLog and
+implement one (or both) of @e DoLog() and @e DoLogString() in it. The second
+one is enough if you're happy with the standard wxLog message formatting
+(prepending "Error:" or "Warning:", timestamping @&c) but just want to send
+the messages somewhere else. The first one may be overridden to do whatever
+you want but you have to distinguish between the different message types
+yourself.
+
+There are some predefined classes deriving from wxLog and which might be
+helpful to see how you can create a new log target class and, of course, may
+also be used without any change. There are:
+
+@li wxLogStderr: This class logs messages to a <tt>FILE *</tt>, using stderr by
+ default as its name suggests.
+@li wxLogStream: This class has the same functionality as wxLogStderr, but uses
+ @e ostream and cerr instead of <tt>FILE *</tt> and stderr.
+@li wxLogGui: This is the standard log target for wxWidgets applications (it is
+ used by default if you don't do anything) and provides the most reasonable
+ handling of all types of messages for given platform.
+@li wxLogWindow: This log target provides a "log console" which collects all
+ messages generated by the application and also passes them to the previous
+ active log target. The log window frame has a menu allowing user to clear
+ the log, close it completely or save all messages to file.
+@li wxLogBuffer: This target collects all the logged messages in an internal
+ buffer allowing to show them later to the user all at once.
+@li wxLogNull: The last log class is quite particular: it doesn't do anything.
+ The objects of this class may be instantiated to (temporarily) suppress
+ output of @e wxLogXXX() functions. As an example, trying to open a
+ non-existing file will usually provoke an error message, but if for some
+ reasons it is unwanted, just use this construction:
+ @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
+
+The log targets can also be combined: for example you may wish to redirect the
+messages somewhere else (for example, to a log file) but also process them as
+normally. For this the wxLogChain, wxLogInterposer, and wxLogInterposerTemp can
+be used.
+
+*/
projects / wxWidgets.git / commitdiff
