NAME
unifdef,
unifdefall —
remove preprocessor conditionals from code
SYNOPSIS
unifdef |
[-ceklst]
[-Ipath]
[-Dsym[=val]]
[-Usym]
[-iDsym[=val]]
[-iUsym]
... [-o
output]
[file] |
unifdefall |
[-Ipath]
... file |
DESCRIPTION
The
unifdef utility selectively processes conditional
cpp(1) directives. It removes from
a file both the directives and any additional text that they specify should be
removed, while otherwise leaving the file alone.
The
unifdef utility acts on
#if,
#ifdef,
#ifndef,
#elif,
#else, and
#endif lines, and it
understands only the commonly-used subset of the expression syntax for
#if and
#elif lines. It handles integer
values of symbols defined on the command line, the
defined()
operator applied to symbols defined or undefined on the command line, the
operators
!,
<,
>,
<=,
>=,
==,
!=,
&&,
||, and
parenthesized expressions. Anything that it does not understand is passed
through unharmed. It only processes
#ifdef and
#ifndef directives if the symbol is specified on the command
line, otherwise they are also passed through unchanged. By default, it ignores
#if and
#elif lines with constant
expressions, or they may be processed by specifying the
-k
flag on the command line.
The
unifdef utility also understands just enough about C to
know when one of the directives is inactive because it is inside a comment, or
affected by a backslash-continued line. It spots unusually-formatted
preprocessor directives and knows when the layout is too odd to handle.
A script called
unifdefall can be used to remove all
conditional
cpp(1) directives from
a file. It uses
unifdef -s and
cpp -dM to get lists of all the
controlling symbols and their definitions (or lack thereof), then invokes
unifdef with appropriate arguments to process the file.
Available options:
- -Dsym[=val]
- Specify that a symbol is defined, and optionally specify
what value to give it for the purpose of handling #if
and #elif directives.
- -Usym
- Specify that a symbol is undefined. If the same symbol
appears in more than one argument, the last occurrence dominates.
- -c
- If the -c flag is specified, then the
operation of unifdef is complemented, i.e., the lines
that would have been removed or blanked are retained and vice versa.
- -e
- Because unifdef processes its input one
line at a time, it cannot remove preprocessor directives that span more
than one line. The most common example of this is a directive with a
multi-line comment hanging off its right hand end. By default, if
unifdef has to process such a directive, it will
complain that the line is too obfuscated. The -e option
changes the behaviour so that, where possible, such lines are left
unprocessed instead of reporting an error.
- -k
- Process #if and #elif
lines with constant expressions. By default, sections controlled by such
lines are passed through unchanged because they typically start
“
#if 0
” and are used as a kind of
comment to sketch out future or past development. It would be rude to
strip them out, just as it would be for normal comments.
- -l
- Replace removed lines with blank lines instead of deleting
them.
- -o
output
- The argument given is the name of an
output file to be used instead of the standard
output. This file can be the same as the input file.
- -s
- Instead of processing the input file as usual, this option
causes unifdef to produce a list of symbols that appear
in expressions that unifdef understands. It is useful in
conjunction with the -dM option of
cpp(1) for creating
unifdef command lines.
- -t
- Disables parsing for C comments and line continuations,
which is useful for plain text.
- -iDsym[=val]
-
- -iUsym
- Ignore #ifdefs. If your C code uses
#ifdefs to delimit non-C lines, such as comments or code
which is under construction, then you must tell unifdef
which symbols are used for that purpose so that it will not try to parse
comments and line continuations inside those #ifdefs.
One specifies ignored symbols with
-iDsym[=val]
and -iUsym similar to
-Dsym[=val]
and -Usym above.
- -Ipath
- Specifies to unifdefall an additional
place to look for #include files. This option is ignored
by unifdef for compatibility with
cpp(1) and to simplify the
implementation of unifdefall.
The
unifdef utility copies its output to
stdout and will take its input from
stdin
if no
file argument is given.
The
unifdef utility works nicely with the
-Dsym option of
diff(1).
DIAGNOSTICS
- Too many levels of nesting.
- Inappropriate #elif,
#else or #endif.
- Obfuscated preprocessor control line.
- Premature
EOF
(with the line
number of the most recent unterminated #if).
EOF
in comment.
The
unifdef utility exits 0 if the output is an exact copy of
the input, 1 if not, and 2 if in trouble.
SEE ALSO
cpp(1),
diff(1)
HISTORY
The
unifdef command appeared in
4.3BSD. ANSI C support was added in
FreeBSD 4.7.
BUGS
Expression evaluation is very limited.
Preprocessor control lines split across more than one physical line (because of
comments or backslash-newline) cannot be handled in every situation.
Trigraphs are not recognized.
There is no support for symbols with different definitions at different points
in the source file.
The text-mode and ignore functionality does not correspond to modern
cpp(1) behaviour.