Preprocessor
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A preprocessor is a program that takes text and performs lexical conversions on it. The conversions may include macro substitution, conditional inclusion, and inclusion of other files.
The use of preprocessors has been getting less common as recent languages provide more abstract features rather than lexical-oriented ones. Indeed, the overuse of the preprocessor might yield quite chaotic code. In designing a new language based on C, Stroustrup introduced features such as inline and templates into C++ in an attempt to make the C preprocessor less relevant. Nevertheless, there is an abundance of installed C code which relies on the preprocessor.
New languages proposed recently have little or no preprocessor ability. Java has no preprocessor. D, designed as a replacement of C and C++, supports features such as imports, nested functions, versioning, debug statements, etc. that help make it practical to eliminate the preprocessor entirely.
Other preprocessors include m4 and Oracle Pro*C. The m4 preprocessor is general-purpose; Oracle Pro*C converts embedded PL/SQL into C.
Preprocessing can be quite cumbersome in incremental parsing or incremental lexical analysis because changes to preprocessing rules can affect the entire text to be preprocessed.
Most C compilers have a flag which allows generation of post-processed code so that static analysis can be performed on the output if desired.