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Message Callback
For portability reasons, the library does not assume the availability
of a terminal, so it does not initially know where to print messages
to. The library generates some messages about its progress as well
as more serious warnings and errors. An application should provide a
message callback that displays them. The function might also choose to
ignore informative messages and only display the fatal ones.
A Message Callback takes three parameters. The first one is the opaque
data pointer of type void*. The second one is a text message
of more or less arbitrary length without line breaks. The last
parameter is an indicator of the seriousness of this message. A string
representation of the warning level is also prefixed to the message.
- UUMSG_MESSAGE
- This is just a plain informative message, nothing important. The
application can choose to simply ignore the message. If a log file
is available, it should be logged, but the message should never result
in a modal dialogue.
- UUMSG_NOTE
- ``Note:''
Still an informative message, meaning that the library made a decision
on its own that might interest the user. One example for a note is
that the setuid bit has been stripped from a file mode for security
reasons. Notes are nothing serious and may still be ignored.
- UUMSG_WARNING
- ``Warning:''
A warning indicates that a non-serious problem occurred which did not
stop the library from proceeding with the current action. One example
is a temporary file that could not be removed. Warnings should be
displayed, but an application may decide to continue even without user
intervention.
- UUMSG_ERROR
- ``ERROR:''
A problem occurred that caused termination of the current request, for
example if the library tried to access a non-existing file. After an
error has occurred, the application should closely examine the
resulting return code of the operation. Error messages are usually
printed in modal dialogues; another option is to save the error
message string somewhere and later print the error message after the
application has examined the operation's return value.
- UUMSG_FATAL
- ``Fatal Error:''
This would indicate that a serious problem has occurred that prevents
the library from processing any more requests. Currently unused.
- UUMSG_PANIC
- ``Panic:''
Such a message would indicate a panic condition, meaning the
application should terminate without further clean-up handling.
Unused so far.3
Next: Busy Callback
Up: Callback Functions
Previous: Intro
2005-01-26