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com_err(3) [linux man page]

COM_ERR(3)						     Library Functions Manual							COM_ERR(3)

NAME
com_err - common error display routine SYNOPSIS
#include <et/com_err.h> void (*proc) (const char *, long, const char *, va_list); void com_err (const char *whoami, long code, const char *format, ...); proc = set_com_err_hook (proc); proc = reset_com_err_hook (); void initialize_XXXX_error_table (); DESCRIPTION
Com_err displays an error message on the standard error stream stderr (see stdio(3S)) composed of the whoami string, which should specify the program name or some subportion of a program, followed by an error message generated from the code value (derived from compile_et(1)), and a string produced using the format string and any following arguments, in the same style as fprintf(3). The behavior of com_err can be modified using set_com_err_hook; this defines a procedure which is called with the arguments passed to com_err, instead of the default internal procedure which sends the formatted text to error output. Thus the error messages from a program can all easily be diverted to another form of diagnostic logging, such as syslog(3). Reset_com_err_hook may be used to restore the behav- ior of com_err to its default form. Both procedures return the previous ``hook'' value. These ``hook'' procedures must have the declara- tion given for proc above in the synopsis. The initialize_XXXX_error_table routine is generated mechanically by compile_et(1) from a source file containing names and associated strings. Each table has a name of up to four characters, which is used in place of the XXXX in the name of the routine. These routines should be called before any of the corresponding error codes are used, so that the com_err library will recognize error codes from these tables when they are used. The com_err.h header file should be included in any source file that uses routines from the com_err library; executable files must be linked using ``-lcom_err'' in order to cause the com_err library to be included. SEE ALSO
compile_et(1), syslog(3). Ken Raeburn, "A Common Error Description Library for UNIX". SIPB
22 Nov 1988 COM_ERR(3)

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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 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
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