<programming> A program that transforms input data in some way before it is read by the main program. In the case of a compiler, the input is source code. The main advantage of using a preprocessor is that it is possible to change the specification of the input data without changing the main program. The separation can also help to make the system's overall behaviour easier to understand. The disadvantage is that performance may be reduced by the extra input and output performed between the two programs. For example, the C preprocessor, cpp, handles textual macro substitution (it acts as a "macro preprocessor"), conditional compilation and inclusion of other files. A preprocessor may be used to transform a program into a simpler language, e.g. to transform C++ into C. (2007-04-05)

In computer science, a preprocessor (or precompiler) is a program that processes its input data to produce output that is used as input to another program. The output is said to be a preprocessed form of the input data, which is often used by some subsequent programs like compilers.

To prevent a section of code from being compiled by surrounding it with a conditional compilation directive whose condition is always false. The canonical examples of these directives are "#if 0" (or "#ifdef notdef", though some find the latter bletcherous) and "#endif" in C. Compare comment out. [Jargon File] (1994-11-30)

<tool, programming> (cpp) The standard Unix macro-expansion utility run as the first phase of the C compiler, cc. Cpp interprets lines beginning with "#" such as #define BUFFER_SIZE 256 as a textual assignment giving the symbol BUFFER_SIZE a value "256". Symbols defined with cpp are traditionally given upper case names to distinguish them from C identifiers. This symbol can be used later in the input, as in char input_buffer[BUFFER_SIZE]; This use of cpp to name constants, rather than writing these magic numbers inline, makes a program easier to read and maintain, especially if there is more than one occurrence of BUFFER_SIZE all of which must all have the same value. Cpp macros can have parameters: #define BIT(n) (1<<(n)) This can be used with any appropriate actual argument: msb = BIT(nbits-1); Note the parentheses around the "n" in the definition of BIT. Without these, operator precedence might mean that the expression substituted in place of n might not be interpreted correctly (though the example above would be OK). Cpp also supports conditional compilation with the use of #ifdef SYMBOL ... #else ... #endif and #if EXPR ... #else ... #endif constructs, where SYMBOL is a Cpp symbol which may or may not be defined and EXPR is an arithmetic expression involving only Cpp symbols, constants and C operators which Cpp can evaluate to a constant at compile time. Decus cpp is a free implementation for VMS. The most widely used C preprocessor today is the GNU CPP, distributed as part of GCC. (2001-12-31)

<World-Wide Web, programming> (PHP) An Open Source, server-side, cross-platform, scripting language used to create dynamic web pages. PHP can be embedded in HTML using special tags like: < ? php echo ' < p > Hello World < /p >'; ? > This is stored in a file with a ".php" extension. The {web server} passes the file to the PHP interpreter which executes the code in the < ? php ... ? > tags. This generates ordinary HTML to send to the web browser. PHP is a recursive acronym. Latest version: 5.2.3 2007-05-31, as of 2007-08-10. PHP Home (http://php.net/). {Cheat sheet (http://www.ilovejackdaniels.com/cheat-sheets/php-cheat-sheet/)}. (2007-08-10)

The Kinetic PreProcessor (KPP) is an open-source software tool used in atmospheric chemistry. Taking a set of chemical reactions and their rate coefficients as input, KPP generates Fortran 90, FORTRAN 77, C, or Matlab code

The PL/I preprocessor is the preprocessor for the PL/I computer programming language. The preprocessor interprets a subset of the full PL/I language to perform source file inclusion, conditional compilation, and macro expansion.

In computer programming, a directive or pragma (from "pragmatic") is a language construct that specifies how a compiler (or other translator) should process its input. Directives are not part of the grammar of a programming language, and may vary from compiler to compiler.

A general-purpose macro processor or general purpose preprocessor is a macro processor that is not tied to or integrated with a particular language or piece of software.