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+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.