A C preprocessor is a part of a C compiler responsible for macro
replacement, conditional compilation and inclusion of header files.
It is often found as a stand-alone program on Unix systems.

ucpp is such a preprocessor; it is designed to be quick and light,
but anyway fully compliant to the ISO standard 9899:1999, also known
as C99. ucpp can be compiled as a stand-alone program, or linked to
some other code; in the latter case, ucpp will output tokens, one
at a time, on demand, as an integrated lexer.

ucpp operates in two modes:
-- lexer mode: ucpp is linked to some other code and outputs a stream of
tokens (each call to the lex() function will yield one token)
-- non-lexer mode: ucpp preprocesses text and outputs the resulting text
to a file descriptor; if linked to some other code, the cpp() function
must be called repeatedly, otherwise ucpp is a stand-alone binary.