set_com_err_hook man page on NetBSD

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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 dis‐
     play library

LIBRARY
     Common Error Library (libcom_err, -lcom_err)

SYNOPSIS
     #include <stdio.h>
     #include <stdarg.h>
     #include <krb5/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 com‐
	      paction 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 dae‐
	      mons to use a routine which calls syslog(3), or in a window sys‐
	      tem 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
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