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The C preprocessor is a macro processor that is used automatically by the C compiler to transform your program before actual compilation. It is called a macro processor because it allows you to define macros, which are brief abbreviations for longer constructs.
The C preprocessor provides four separate facilities that you can use as you see fit:
C preprocessors vary in some details. This manual discusses the GNU C preprocessor, the C Compatible Compiler Preprocessor. The GNU C preprocessor provides a superset of the features of ANSI Standard C.
ANSI Standard C requires the rejection of many harmless constructs commonly used by today's C programs. Such incompatibility would be inconvenient for users, so the GNU C preprocessor is configured to accept these constructs by default. Strictly speaking, to get ANSI Standard C, you must use the options `-trigraphs', `-undef' and `-pedantic', but in practice the consequences of having strict ANSI Standard C make it undesirable to do this. See section 1.9 Invoking the C Preprocessor.
The C preprocessor is designed for C-like languages; you may run into problems if you apply it to other kinds of languages, because it assumes that it is dealing with C. For example, the C preprocessor sometimes outputs extra white space to avoid inadvertent C token concatenation, and this may cause problems with other languages.
1.1 Transformations Made Globally Actions made uniformly on all input files. 1.2 Preprocessing Directives General syntax of preprocessing directives. 1.3 Header Files How and why to use header files. 1.4 Macros How and why to use macros. 1.5 Conditionals How and why to use conditionals. 1.6 Combining Source Files Use of line control when you combine source files. 1.7 Miscellaneous Preprocessing Directives Miscellaneous preprocessing directives. 1.8 C Preprocessor Output Format of output from the C preprocessor. 1.9 Invoking the C Preprocessor How to invoke the preprocessor; command options. Concept Index Index of concepts and terms. Index of Directives, Macros and Options Index of directives, predefined macros and options.
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