Case Study

I now introduce a case study of a real-world function library manual, in particular the manual for the getc, fgetc, getw, and getchar functions from OpenBSD. The original file may be viewed on-line at src/lib/libc/stdio/getc.3, file version 1.12. This is not the manual for the full function library, but only a handful of similar functions.

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This is the standard comment header to manual files in OpenBSD. The $OpenBSD$ line is automatically updated by the revision control system, cvs, whenever an update to the file is committed. The line following is the copyright message, and following that is the text form of the BSD license.

.Dd $Mdocdate: May 31 2007 $
.Dt GETC 3
.Os

This classifies our manual in category 3 as a function or function library. The title of the manual, GETC, is chosen as the most general of those functions listed below in the NAME section.

.Sh NAME
.Nm fgetc ,
.Nm getc ,
.Nm getchar ,
.Nm getw
.Nd get next character or word from input stream

Lists (alphabetically) all the functions that will be documented, and some general notes about their collective function. We next jump down into the SYNOPSIS; since this set of functions is part of the C Standard Library, it needs no special linking information.

.Sh SYNOPSIS
.Fd #include <stdio.h>
.Ft int
.Fn fgetc "FILE *stream"
.Ft int
.Fn getc "FILE *stream"
.Ft int
.Fn getchar "void"
.Ft int
.Fn getw "FILE *stream"

This documents the calling syntax of all functions. Note that the Fd macro is used instead of the In macro. This invocation is historically relevant, but new manuals should always use In.

Next, each function and its arguments is explained as a free-flowing paragraph. This was probably chosen instead of using a list item for each argument (with Bl) due to the small number of arguments.

.Sh DESCRIPTION
The
.Fn fgetc
function obtains the next input character (if present) from the stream
pointed at by
.Fa stream ,
or the next character pushed back on the stream via
.Xr ungetc 3 .
.Pp
The
.Fn getc
function acts essentially identically to
.Fn fgetc ,
but is a macro that expands in-line.
.Pp
The
.Fn getchar
function is equivalent to
.Fn getc
with the argument
.Em stdin .
.Pp
The
.Fn getw
function obtains the next
.Li int
(if present)
from the stream pointed at by
.Fa stream .

The usage of the Em macro is not correct: the Va or Dv macro would have been more appropriate. The same applies to the Li. The mdoc language is semantic, so using presentation macros such as Li and Em is discouraged.

.Sh RETURN VALUES
If successful, these routines return the next requested object from the
.Fa stream .
If the stream is at end-of-file or a read error occurs, the routines return
.Dv EOF .
The routines
.Xr feof 3 and
.Xr ferror 3
must be used to distinguish between end-of-file and error.
If an error occurs, the global variable
.Va errno
is set to indicate the error.
The end-of-file condition is remembered, even on a terminal, and all
subsequent attempts to read will return
.Dv EOF
until the condition is cleared with
.Xr clearerr 3 .
.Sh SEE ALSO
.Xr ferror 3 ,
.Xr fopen 3 ,
.Xr fread 3 ,
.Xr putc 3 ,
.Xr ungetc 3

All possible return values are correctly documented in the RETURN VALUES section and relevant functions cross-linked in the SEE ALSO section. Note that the cross-linked manuals are also alphabetically sorted.

.Sh STANDARDS
The
.Fn fgetc ,
.Fn getc ,
and
.Fn getchar
functions conform to
.St -ansiC .

Noting standards conformance is extremely important: it allows programmers and administrators to depend on your component in a cross-platform fashion. These functions are part of the C Standard Library.

.Sh BUGS
Since
.Dv EOF
is a valid integer value,
.Xr feof 3
and
.Xr ferror 3
must be used to check for failure after calling
.Fn getw .
.Pp
Since the size and byte order of an
.Vt int
may vary from one machine to another,
.Fn getw
is not recommended for portable applications.

The BUGS section should be used very carefully — bugs preferably should be fixed. In this section, design bugs have been documented. Whether the CAVEATS section would be more appropriate is up to the manual author.

We found several inconsistent uses of mdoc in this manual. In general, if you find unusual or erroneous macros or styles in UNIX manuals, notify the authors! A bug in a manual is just as important as a bug in the code.