NAME¶
unifdef,
unifdefall —
remove preprocessor conditionals from code
SYNOPSIS¶
unifdef |
[-bBcdeKknsStV]
[-Ipath]
[-Dsym[=val]]
[-Usym]
[-iDsym[=val]]
[-iUsym]
... [-o
outfile]
[infile] |
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. A directive is
only processed if the symbols specified on the command line are sufficient to
allow
unifdef to get a definite value for its control
expression. If the result is false, the directive and the following lines
under its control are removed. If the result is true, only the directive is
removed. An
#ifdef or
#ifndef directive is
passed through unchanged if its controlling symbol is not specified on the
command line. Any
#if or
#elif control
expression that has an unknown value or that
unifdef cannot
parse is passed through unchanged. By default,
unifdef
ignores
#if and
#elif lines with constant
expressions; it can be told to process them by specifying the
-k flag on the command line.
It understands a commonly-used subset of the expression syntax for
#if and
#elif lines: integer constants,
integer values of symbols defined on the command line, the
defined() operator, the operators
!,
<,
>,
<=,
>=,
==,
!=,
&&,
||, and parenthesized
expressions. A kind of “short circuit” evaluation is used for the
&& operator: if either operand is definitely false
then the result is false, even if the value of the other operand is unknown.
Similarly, if either operand of
|| is definitely true then
the result is true.
In most cases, the
unifdef utility does not distinguish
between object-like macros (without arguments) and function-like arguments
(with arguments). If a macro is not explicitly defined, or is defined with the
-D flag on the command-line, its arguments are ignored. If a
macro is explicitly undefined on the command line with the
-U flag, it may not have any arguments since this leads to a
syntax error.
The
unifdef utility 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 for it 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.
OPTIONS¶
- -Dsym=val
- Specify that a symbol is defined to a given value which is
used when evaluating #if and #elif
control expressions.
- -Dsym
- Specify that a symbol is defined to the value 1.
- -Usym
- Specify that a symbol is undefined. If the same symbol
appears in more than one argument, the last occurrence dominates.
- -b
- Replace removed lines with blank lines instead of deleting
them. Mutually exclusive with the -B option.
- -B
- Compress blank lines around a deleted section. Mutually
exclusive with the -b option.
- -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.
- -d
- Turn on printing of debugging messages.
- -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
- Always treat the result of && and
|| operators as unknown if either operand is unknown,
instead of short-circuiting when unknown operands can't affect the result.
This option is for compatibility with older versions of
unifdef.
- -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.
- -n
- Add
#line
directives to the output
following any deleted lines, so that errors produced when compiling the
output file correspond to line numbers in the input file.
- -o
outfile
- Write output to the file outfile
instead of the standard output. If outfile is the
same as the input file, the output is written to a temporary file which is
renamed into place when unifdef completes successfully.
- -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.
- -S
- Like the -s option, but the nesting depth
of each symbol is also printed. This is useful for working out the number
of possible combinations of interdependent defined/undefined symbols.
- -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.
You can specify 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.
- -V
- Print version details.
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).
EXIT STATUS¶
The
unifdef utility exits 0 if the output is an exact copy of
the input, 1 if not, and 2 if in trouble.
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.
SEE ALSO¶
cpp(1),
diff(1)
HISTORY¶
The
unifdef command appeared in
2.9BSD. ANSI C support was added in
FreeBSD 4.7.
AUTHORS¶
The original implementation was written by
Dave Yost
⟨Dave@Yost.com⟩.
Tony Finch ⟨dot@dotat.at⟩ rewrote it to
support ANSI C.
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.