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(com_err.info)Why com_err?

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Why com_err?
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   In building application software packages, a programmer often has to
deal with a number of libraries, each of which can use a different
error-reporting mechanism.  Sometimes one of two values is returned,
indicating simply SUCCESS or FAILURE, with no description of errors
encountered.  Sometimes it is an index into a table of text strings,
where the name of the table used is dependent on the library being used
when the error is generated; since each table starts numbering at 0 or
1, additional information as to the source of the error code is needed
to determine which table to look at.  Sometimes no text messages are
supplied at all, and the programmer must supply them at any point at
which he may wish to report error conditions.  Often, a global variable
is assigned some value describing the error, but the programmer has to
know in each case whether to look at `errno', `h_errno', the return
value from `hes_err()', or whatever other variables or routines are
specified.  And what happens if something in the procedure of examining
or reporting the error changes the same variable?

   The package we have developed is an attempt to present a common
error-handling mechanism to manipulate the most common form of error
code in a fashion that does not have the problems listed above.

   A list of up to 256 text messages is supplied to a translator we have
written, along with the three- to four-character "name" of the error
table.  The library using this error table need only call a routine
generated from this error-table source to make the table "known" to the
com_err library, and any error code the library generates can be
converted to the corresponding error message.  There is also a default
format for error codes accidentally returned before making the table
known, which is of the form `unknown code foo 32', where `foo' would be
the name of the table.