LogIO.h

Classes

LogIO -- ostream-like interface to creating log messages. (full description)

Global Functions -- Functions to send commands to a LogIO object. (full description)

Global Functions -- Functions to accumulate text in the output message. (full description)

class LogIO

Types

enum Command

POST
Post the accumulated message. Equivalent to calling LogIO::post().

EXCEPTION
Post the accumulated message then throw an exception. Always posts the message at SEVERE priority. Equivalent to calling LogIO::postThenThrow().

SEVERE
Change the message priority to SEVERE.

WARN
Change the message priority to WARN.

NORMAL
Change the message priority to NORMAL.

DEBUGGING
Change the message priority to DEBUGGING.

Interface

Public Members

LogIO()

LogIO(LogSink &sink)

LogIO(const LogOrigin &OR)

LogIO(const LogOrigin &OR, LogSink &sink)

LogIO(const LogIO &other)

LogIO &operator=(const LogIO &other)

~LogIO()

void post()

void postLocally()

void postThenThrow()

void priority(LogMessage::Priority which)

void sourceLocation(const SourceLocation *where)

void origin(const LogOrigin &origin)

ostream& output()

LogSinkInterface &localSink()

const LogSinkInterface &localSink() const

Description

Review Status

Reviewed By:

UNKNOWN

Date Reviewed:

before2004/08/25

Programs:

Demos:

dLogging.cc

Tests:

tLogIO.cc

Prerequisite

LogSink class
LogMessage class
LogOrigin class

Etymology

Log message, Input/Output.

Synopsis

LogIO is intended to be used in a way similar to the ostream class. However, rather than sending it's output to a file or stdout, it bundles its output up into LogMessage objects and posts them to a LogSink.

When you use the "<<" operator on a LogIO, you are building up a log message inside the LogIO object. The message is posted when:

LogIO::post() is called
You send the LogIO::POST or LogIO::EXCEPTION commands to the LogIO with the shift ( << ) command.
The LogIO object is destructed.

Note that log messages may span multiple lines, so sending the LogIO a newline (via "\n" or endl) does not force the message to be emitted.

Example

A LogIO may be created in the following ways:

    LogIO   os;

Here, os is attached to the global log sink, and no origin information is set.

    TableLogSink tab(...);
    LogIO   os(tab);

Here, os is attached to tab (and also to the global log sink since every sink's post also calls the global sink's post).

    LogIO   os(LogOrigin("class", "func(args)", WHERE));

Here, os is attached to the global sink and the origin information is set to class::func(args) and the line number and source file information is set (with WHERE).

    TableLogSink tab(...);
    LogIO   os(LogOrigin("class", "func(args)", WHERE), tab);

Here all the above information is set.

Once you have a LogIO, using it is pretty simple:

   os << "Every good boy deserves" << 5 << " pieces of fudge!";

This accumulates the message but does not send it. If you want to force it to be sent you can do so with either of the following methods:

    os << LogIO::POST;     // From the Commands enum
    os.post();             // Member function

Note that after a post the priority is reset to NORMAL.

If you want to change the level of the message you can also do so with the shift operator:

   os << LogIO::DEBUGGING << "Boring message" << 
         LogIO::SEVERE << "Error!" << LogIO::POST;

Note that changing the priority changes the priority of the entire message. The message does not get posted until the POST is done. So in the above example the DEBUGGING priority does not do anything because the priority is overwritten by the SEVERE one.

You can also change the origin information with the << operator:

    os << LogOrigin("class", "func(args)");
    os << WHERE;

Motivation

The earlier method of creating log messages solely through LogSink and LogMessage required the programmer to type in more lines of code than this solution. Also, this interface makes it easy to drop log messages into existing code that uses ostreams.

To Do

Add << operators for all classes that have ostream<< defined. (We could probably do it with a template, but might result in ambiguity).
Have a function for changing the LogSink only? (You can get much the same effect with operator=). them?

Member Description

enum Command

Special commands to the LogIO object

LogIO()

Attach this LogIO object to the global sink with no origin information.

LogIO(LogSink &sink)

Attach this LogIO object to the supplied sink. A referencing copy of the sink is made inside the LogIO object, so you do not need to worry about memory management.

LogIO(const LogOrigin &OR)

Attach this LogIO object to the supplied origin and global sink.

LogIO(const LogOrigin &OR, LogSink &sink)

Attach this LogIO object to the supplied origin and sink.

LogIO(const LogIO &other)
LogIO &operator=(const LogIO &other)

Copying uses reference semantics, i.e. the same sink will be shared by both copies.

~LogIO()

The destructor will post any accumulated message that has not already been posted.

void post()

Post the accumulated message. If you wish, you can post the messages only locally to the sink. After the post the priority is reset to NORMAL.

void postLocally()

Post the accumulated message locally. After the post the priority is reset to NORMAL.

void postThenThrow()

Post the accumulated message at SEVERE priority and then throw an exception. After the post the priority is reset to NORMAL.

void priority(LogMessage::Priority which)

Change the priority of the message. It does NOT post the accumulated message at the old priority first.

void sourceLocation(const SourceLocation *where)

Change the location in the origin. Almost always this is called with the macro WHERE as its argument.

void origin(const LogOrigin &origin)

Change the origin of the accumulated message.

ostream& output()

Acumulate output in this ostream.

LogSinkInterface &localSink()

Occasionally it is useful to interrogate the local log sink.

const LogSinkInterface &localSink() const

Functions to send commands to a LogIO object. (source)

Interface

Private Members

LogIO &operator<<(LogIO &os, LogIO::Command item)

LogIO &operator<<(LogIO &os, const SourceLocation *item)

LogIO &operator<<(LogIO &os, const LogOrigin &OR)

Description

The following commands don't change the accumulated message, rather they send commands to the LogIO object, either to:

post the current message: os << "message" << LogIO::POST;
post the current message and then throw an exception: os << "error" << LogIO::EXCEPTION;
Change the priority of the current message: os << LogIO::DEBUGGING;

Change the origin of the message:

          os << LogOrigin(...);
          os << WHERE;             // Changes only source file/line number

Member Description

LogIO &operator<<(LogIO &os, LogIO::Command item)

LogIO &operator<<(LogIO &os, const SourceLocation *item)

LogIO &operator<<(LogIO &os, const LogOrigin &OR)

Functions to accumulate text in the output message. (source)

Interface

LogIO &operator<<(LogIO &os, const String &item)

LogIO &operator<<(LogIO &os, const char *item)

LogIO &operator<<(LogIO &os, Double item)

LogIO &operator<<(LogIO &os, Complex item)

LogIO &operator<<(LogIO &os, DComplex item)

LogIO &operator<<(LogIO &os, Int item)

LogIO &operator<<(LogIO &os, uInt item)

LogIO &operator<<(LogIO &os, uLong item)

LogIO &operator<<(LogIO &os, Long item)

LogIO &operator<<(LogIO &os, Bool item)

LogIO &operator<<(LogIO &os, ostream &(*item)(ostream &))

Description

Accumulate text in the output message. The last entry is for things like endl.