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man page of unifdef

unifdef: remove preprocessor conditionals from code


unifdef, unifdefall - remove preprocessor conditionals from code
unifdef [-bBcdeKknsStV] [-Ipath] [-Dsym[=val]] [-Usym] [-iDsym[=val]] [-iUsym] ... [-o outfile] [infile] unifdefall [-Ipath] ... file
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.


-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).


The unifdef utility exits 0 if the output is an exact copy of the input, 1 if not, and 2 if in trouble.


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.


cpp(1), diff(1)
The unifdef command appeared in 2.9BSD. ANSI C support was added in FreeBSD 4.7.
The original implementation was written by Dave Yost <Dave@Yost.com>. Tony Finch <dot@dotat.at> rewrote it to support ANSI C.


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. January 18, 2011 UNIFDEF(1)

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