explain_output(3)					     Library Functions Manual						 explain_output(3)

NAME

       explain_output - output error messages

SYNOPSIS

       #include <libexplain/output.h>

DESCRIPTION

       These functions may be used to write error messages.

   explain_output_message
       void explain_output_message(const char *text);

       The  explain_output_message  function is used to print text.  It is printed via the registered output class, see explain_output_register(3)
       for how.

       text    The text of the message to be printed.  It has not been wrapped (yet).

   explain_output_error
       void explain_output_error(const char *fmt, ...);

       The explain_output_error function is used to print a formatted error message.  The printing is done via the explain_output_message(3) func-
       tion.

       fmt     The format text of the message to be printed.  See printf(3) for more information.

   explain_output_error_and_die
       void explain_output_error_and_die(const char *fmt, ...);

       The explain_output_error_and_die function is used to print text, and then terminate immediately.  The printing is done via the explain_out-
       put_message(3) function, process termination is via the explain_output_exit_failure(3) function.

       fmt     The format text of the message to be printed.  See printf(3) for more information.

   explain_output_warning
       void explain_output_warning(const char *fmt, ...);

       The explain_output_warning function is used to print a formatted error message, including the word "warning".  The printing is done via the
       explain_output_message(3) function.

       fmt     The format text of the message to be printed.  See printf(3) for more information.

   explain_output_exit
       void explain_output_exit(int status);

       The  explain_output_exit  function  is  used to terminate execution.  It is executed via the registered output class, explain_output_regis-
       ter(3) for how.

       status  The exist status requested.

   explain_output_exit_failure
       void explain_output_exit_failure(void);

       The explain_output_exit_failure function is used to terminate execution, with exit status EXIT_FAILURE.	It is executed via the	registered
       output class, see explain_output_register(3) for how.

   explain_option_hanging_indent_set
       void explain_option_hanging_indent_set(int columns);

       The  explain_option_hanging_indent_set  function is used to cause the output wrapping to use hanging indents.  By default no hanging indent
       is used, but this can sometimes obfuscate the end of one error message and the beginning of another.  A hanging indent results in continua-
       tion lines starting with white space, similar to RFC822 headers.

       This can be set using the "hanging-indent=n" string in the EXPLAIN_OPTIONS environment variable.  See explain(3) for more information.

       Using this function will override any environment variable setting.

       columns The  number  of	columns of hanging indent to be used.  A value of 0 means no hanging indent (all lines flush with left margin).  A
	       common value to use is 4: it doesn't consume too much of each line, and it is a clear indent.

OUTPUT REDIRECTION

       It is possible to change how and where libexplain sends its output, and even how it calls the exit(2) function.	This functionality is used
       by the explain_*_or_die and explain_*_on_error functions.

       By default, libexplain will wrap and print error messages on stderr, and call the exit(2) system call to terminate execution.

       Clients	of  the libexplain library may choose to use some message handling facilities provided by libexplain, or they may choose to imple-
       ment their own.

       syslog
	       To cause all output to be sent to syslog, use

		      explain_output_register(explain_output_syslog_new());

	       This is useful for servers and daemons.

       stderr and syslog
	       The "tee" output class can be used to duplicate output.	To cause all output to be sent to both stderr and syslog, use

		      explain_output_register
		      (
			  explain_output_tee_new
			  (
			      explain_output_stderr_new(),
			      explain_output_syslog_new()
			  )
		      );

	       If you need more than two, use several instances of "tee", cascaded.

       stderr and a file
	       To cause all output to be sent to both stderr and a regular file, use

		      explain_output_register
		      (
			  explain_output_tee_new
			  (
			      explain_output_stderr_new(),
			      explain_output_file_new(filename, 0)
			  )
		      );

       See the <libexplain/output.h> file for extensive documentation.

   explain_output_new
       explain_output_t *explain_output_new(const explain_output_vtable_t *vtable);

       The explain_output_new function may be used to create a new dynamically allocated instance of explain_output_t.

       vtable  The struct containing the pointers to the methods of the derived class.

       returns NULL on error (i.e. malloc failed), or a pointer to a new dynamically allocated instance of the class.

   explain_output_stderr_new
       explain_output_t *explain_output_stderr_new(void);

       The explain_output_stderr_new function may be used to create a new dynamically allocated instance of an explain_output_t class that  writes
       to stderr, and exits via exit(2);

       This is the default output handler.

       returns NULL on error (i.e. malloc failed), or a pointer to a new dynamically allocated instance of the stderr class.

   explain_output_syslog_new
       explain_output_t *explain_output_syslog_new(void);

       The  explain_output_syslog_new function may be used to create a new dynamically allocated instance of an explain_output_t class that writes
       to syslog, and exits via exit(2);

       The following values are used:

	      option = 0
	      facility = LOG_USER
	      level = LOG_ERR

       See syslog(3) for more information.

       returns NULL on error (i.e. malloc(3) failed), or a pointer to a new dynamically allocated instance of the syslog class.

   explain_output_syslog_new1
       explain_output_t *explain_output_syslog_new1(int level);

       The explain_output_syslog_new1 function may be used to create a new dynamically allocated instance of an explain_output_t class that writes
       to syslog, and exits via exit(2);

       The following values are used:

	      option = 0
	      facility = LOG_USER

       See syslog(3) for more information.

       level   The syslog level to be used, see syslog(3) for a definition.

       returns NULL on error (i.e. malloc(3) failed), or a pointer to a new dynamically allocated instance of the syslog class.

   explain_output_syslog_new3
       explain_output_t *explain_output_syslog_new3(int option, int facility, int level);

       The explain_output_syslog_new3 function may be used to create a new dynamically allocated instance of an explain_output_t class that writes
       to syslog, and exits via exit(2);

       If you want different facilities or levels, create multiple instances.

       option  The syslog option to be used, see syslog(3) for a definition.

       facility
	       The syslog facility to be used, see syslog(3) for a definition.

       level   The syslog level to be used, see syslog(3) for a definition.

       returns NULL on error (i.e. malloc(3) failed), or a pointer to a new dynamically allocated instance of the syslog class.

   explain_output_file_new
       explain_output_t *explain_output_file_new(const char *filename, int append);

       The explain_output_file_new function may be used to create a new dynamically allocated instance of an explain_output_t class that writes to
       a file, and exits via exit(2).

       filename
	       The file to be opened and written to.

       append  true (non-zero) if messages are to be appended to the file, false (zero) if the file is to be replaced with new contents.

       returns NULL on error (i.e. malloc(3) or open(2) failed), or a pointer to a new dynamically allocated instance of the syslog class.

   explain_output_tee_new
       explain_output_t *explain_output_tee_new(explain_output_t *first, explain_output_t *second);

       The  explain_output_tee_new function may be used to create a new dynamically allocated instance of an explain_output_t class that writes to
       two other output classes.

       first   The first output class to write to.

       second  The second output class to write to.

       returns NULL on error (i.e. malloc(3) failed), or a pointer to a new dynamically allocated instance of the syslog class.

       The output subsystem will "own" the first and second objects after this call.  You may not make any reference to these pointers ever again.
       The output subsystem will destroy these objects and free the memory when it feels like it.

   explain_output_register
       void explain_output_register(explain_output_t *op);

       The  explain_output_register  function  is  used  to  change libexplain's default output handling facilities with something else.  The NULL
       pointer restores libexplain's default processing.

       If no output class is registered, the default is to wrap and print to stderr, and to exit via the exit(2) system call.

       op      Pointer to the explain_output_t instance to be operated on.

       The output subsystem will "own" the pointer after this call.  You may not make any reference to this pointer ever again.  The  output  sub-
       system will destroy the object and free the memory when it feels like it.

COPYRIGHT

       libexplain version 0.52
       Copyright (C) 2010 Peter Miller

AUTHOR

       Written by Peter Miller <pmiller@opensource.org.au>

																 explain_output(3)