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 degugging 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.
March 11, 2010