COM\_ERR(3) Library Functions Manual COM\_ERR(3) # [NAME](#NAME) com\_err - common error display routine # [SYNOPSIS](#SYNOPSIS) ``` #include 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](#DESCRIPTION) *Com\_err* displays an error message on the standard error stream *stderr* (see [*stdio*(3S)](/man/os/e2fsprogs/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)](/man/os/e2fsprogs/compile_et.1)), and a string produced using the *format* string and any following arguments, in the same style as [*fprintf*(3)](/man/os/e2fsprogs/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)](/man/os/e2fsprogs/syslog.3). *Reset\_com\_err\_hook* may be used to restore the behavior of *com\_err* to its default form. Both procedures return the previous \`\`hook'' value. These \`\`hook'' procedures must have the declaration given for *proc* above in the synopsis. The *initialize\_XXXX\_error\_table* routine is generated mechanically by [*compile\_et*(1)](/man/os/e2fsprogs/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](#SEE_ALSO) [compile\_et (1)](/man/os/e2fsprogs/compile_et.1), [syslog (3)](/man/os/e2fsprogs/syslog.3). Ken Raeburn, "A Common Error Description Library for UNIX". 22 Nov 1988 SIPB --- Document: com_err(3) from e2fsprogs 1.47.4-r3 (Chainguard OS) Source: https://github.com/tytso/e2fsprogs