zapif

zapif algebraic simplifies C proprocessor conditionals and removes code that would never be selected by the preprocessor.

Unlike unifdef, zapif simplifies conditionals that it cannot eliminate. For example, given a file demo.c with:

#if foo && bar || quod
void f() {}
#endif

the command ``zapif -Dbar=1 -Dquod=0 demo.c` will produce:

#if foo
void f() {}
#endif

When simplifying a preprocessor directive, zapif tries to preserve whitespace and the original form of numerals when simplifying. Literal numerals such as 0 and 1 are treated as unknown values unless the -k option is present.

Examples of the simplifications that zapif knows:

• 0 || y -> y
• x || y -> 1 if x or y is nonzero.
• 0 && y -> 0
• 0 | y -> y
• 0 ^ y -> y
• 0 & y -> 0

Algebraic simplifications are limited to ones that seem to be useful for real C++ and C source. If you think I've missed a useful one, please open an issue, ideally with a citation to the source code.

Prequisites

I developed zapif on Mac OS X, but it should build on Linux without difficulty. To build zapif you will need:

• flex 2.5 or 2.6
• bison 2.3 or 3.0
• a C++11 compiler. The default is g++.

Building zapif

1. cd build
2. make

The 2nd step builds the executable and tests it. If the test fails, you will see output from diff.

Using zapif

The basic syntax is:

• zapif options [inputfile]

If no input file is specified, input is stdin. Output always goes to stdout.

The recognized options are:

• -Dfoo=42 - treat foo as having the value 42.
• -Dfoo - same as -Dfoo=1
• -Ufoo - treat foo as undefined. The preprocessor expression defined(foo) will evaluate to 0, and foo will be treated as 0 in other preprocessor expressions.
• -c - assume input is C, not C++. Causes and, false, not, or, true and xor to be treated as identifiers instead of their C++ meanings in #if expressions.
• -k - interpret numerals in preprocessor expressions. Without this option, numerals such as 0 are treated as unknown values.
• -n - normalize #if defined(x) to #ifdef x if the whole expression was the result of simplification. Do likewise for #if !defined(x) and the equivalent parentheses-free forms.
• -v - print version information and exit.

Limitations

• Numerals are recognized as having values only if they fit in a C++ long long, follow the C conventions for decimal, octal, or hexadecimal, and do not have any suffixes.