NAME    [Toc]    [Back]

     com_err, com_err_va, error_message, error_table_name, init_error_table,
     set_com_err_hook, reset_com_err_hook - common error display library

LIBRARY    [Toc]    [Back]

     Common Error Library (libcom_err, -lcom_err)

SYNOPSIS    [Toc]    [Back]

     #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);

DESCRIPTION    [Toc]    [Back]

     The com_err library provides a common error-reporting mechanism for
     defining and accessing error codes and descriptions for application software
 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.

     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    [Toc]    [Back]

     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.

     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.

     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    [Toc]    [Back]

     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    [Toc]    [Back]

     compile_et(1)

BSD                            November 21, 2001                           BSD