The source file name must end with a suffix of ``.et''; the file consists of a declaration supplying the name (up to four characters long) of the error-code table:
followed by up to 256 entries of the form:
error_code name, " string "
and a final
to indicate the end of the table.
The name of the table is used to construct the name of a subroutine initialize_XXXX_error_table which must be called in order for the com_err library to recognize the error table.
The various error codes defined are assigned sequentially increasing numbers (starting with a large number computed as a hash function of the name of the table); thus for compatibility it is suggested that new codes be added only to the end of an existing table, and that no codes be removed from tables.
The names defined in the table are placed into a C header file with preprocessor directives defining them as integer constants of up to 32 bits in magnitude.
A C source file is also generated which should be compiled and linked with the object files which reference these error codes; it contains the text of the messages and the initialization subroutine. Both C files have names derived from that of the original source file, with the ``.et'' suffix replaced by ``.c'' and ``.h''.
A ``#'' in the source file is treated as a comment character, and all remaining text to the end of the source line will be ignored.
Since the original compile_et uses a very simple parser based on yacc(1), and this current version of compile_et uses an awk/sed combination of scripts, its error recovery leaves much to be desired.
Ken Raeburn, "A Common Error Description Library for UNIX".