COM_ERR(3)						   BSD Library Functions Manual 						COM_ERR(3)

NAME

     com_err, com_err_va, error_message, error_table_name, init_error_table, set_com_err_hook, reset_com_err_hook, add_to_error_table,
     initialize_error_table_r free_error_table, com_right -- common error display library

LIBRARY

     Common Error Library (libcom_err, -lcom_err)

SYNOPSIS

     #include <stdio.h>
     #include <stdarg.h>
     #include <com_err.h>
     #include "XXX_err.h"

     typedef void (*errf)(const char *, long, const char *, ...);

     void
     com_err(const char *whoami, long code, const char *format, ...);

     void
     com_err_va(const char *whoami, long code, const char *format, ...);

     const char *
     error_message(long code);

     const char *
     error_table_name(int num);

     int
     init_error_table(const char **msgs, long base, int count);

     errf
     set_com_err_hook(errf func);

     errf
     reset_com_err_hook();

     void
     add_to_error_table(struct et_list *new_table);

     void
     initialize_error_table_r(struct et_list **et_list, const char **msgs, int base, long count);

     void
     free_error_table(struct et_list *);

     const char *
     com_right(struct et_list *list, long, code");

DESCRIPTION

     The com_err library provides a common error-reporting mechanism for defining and accessing error codes and descriptions for application soft-
     ware packages.  Error descriptions are defined in a table and error codes are used to index the table.  The error table, the descriptions and
     the error codes are generated using compile_et(1).

     The error table is registered with the com_err library by calling its initialisation function defined in its header file.	The initialisation
     function is generally defined as initialize_<name>_error_table(), where name is the name of the error table.

     If a thread-safe version of the library is needed initialize_<name>_error_table_r() that internally calls initialize_error_table_r() instead
     be used.

     Any variable which is to contain an error code should be declared <name>_error_number where name is the name of the error table.

FUNCTIONS

     The following functions are available to the application developer:

     com_err(whoami, code, format, ...)
	      Displays an error message on standard error composed of the whoami string, which should specify the program name, followed by an
	      error message generated from code, and a string produced using the printf(3) format string and any following arguments.  If format
	      is NULL, the formatted message will not be printed.  The argument format may not be omitted.

     com_err_va(whoami, code, format, va_list args)
	      This routine provides an interface, equivalent to com_err(), which may be used by higher-level variadic functions (functions which
	      accept variable numbers of arguments).

     error_message(code)
	      Returns the character string error message associate with code.  If code is associated with an unknown error table, or if code is
	      associated with a known error table but is not in the table, a string of the form `Unknown code XXXX NN' is returned, where XXXX is
	      the error table name produced by reversing the compaction performed on the error table number implied by that error code, and NN is
	      the offset from that base value.

	      Although this routine is available for use when needed, its use should be left to circumstances which render com_err() unusable.

	      com_right() returns the error string just like com_err but in a thread-safe way.

     error_table_name(num)
	      Convert a machine-independent error table number num into an error table name.

     init_error_table(msgs, base, count)
	      Initialise the internal error table with the array of character string error messages in msgs of length count.  The error codes are
	      assigned incrementally from base.  This function is useful for using the error-reporting mechanism with custom error tables that
	      have not been generated with compile_et(1).  Although this routine is available for use when needed, its use should be restricted.

	      initialize_error_table_r() initialize the et_list in the same way as init_error_table(), but in a thread-safe way.

     set_com_err_hook(func)
	      Provides a hook into the com_err library to allow the routine func to be dynamically substituted for com_err().  After
	      set_com_err_hook()
	       has been called, calls to com_err() will turn into calls to the new hook routine.  This function is intended to be used in daemons
	      to use a routine which calls syslog(3), or in a window system application to pop up a dialogue box.

     reset_com_err_hook()
	      Turns off the hook set in set_com_err_hook().

     add_to_error_table(new_table)
	      Add the error table, its messages strings and error codes in new_table to the internal error table.

EXAMPLES

     The following is an example using the table defined in compile_et(1):

	     #include <stdio.h>
	     #include <stdarg.h>
	     #include <syslog.h>

	     #include "test_err.h"

	     void
	     hook(const char *whoami, long code,
		     const char *format, va_list args)
	     {
		     char buffer[BUFSIZ];
		     static int initialized = 0;

		     if (!initialized) {
			     openlog(whoami, LOG_NOWAIT, LOG_DAEMON);
			     initialized = 1;
		     }
		     vsprintf(buffer, format, args);
		     syslog(LOG_ERR, "%s %s", error_message(code), buffer);
	     }

	     int
	     main(int argc, char *argv[])
	     {
		     char *whoami = argv[0];

		     initialize_test_error_table();
		     com_err(whoami, TEST_INVAL, "before hook");
		     set_com_err_hook(hook);
		     com_err(whoami, TEST_IO, "after hook");
		     return (0);
	     }

SEE ALSO

     compile_et(1)

BSD
								   July 7, 2005 							       BSD