The C Preprocessor

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The C preprocessor implements the macro language used to transform C, C++, and Objective-C programs before they are compiled. It can also be useful on its own.

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(a) The FSF’s Front-Cover Text is:

A GNU Manual

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© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-9.5.0/cpp/index.html


• Overview:
• Header Files:
• Macros:
• Conditionals:
• Diagnostics:
• Line Control:
• Pragmas:
• Other Directives:
• Preprocessor Output:
• Traditional Mode:
• Implementation Details:
• Invocation:
• Environment Variables:
• GNU Free Documentation License:
• Index of Directives:
• Option Index:
• Concept Index:
— The Detailed Node Listing — Overview
• Character sets:
• Initial processing:
• Tokenization:
• The preprocessing language:
Header Files
• Include Syntax:
• Include Operation:
• Search Path:
• Once-Only Headers:
• Alternatives to Wrapper #ifndef:
• Computed Includes:
• Wrapper Headers:
• System Headers:
Macros
• Object-like Macros:
• Function-like Macros:
• Macro Arguments:
• Stringizing:
• Concatenation:
• Variadic Macros:
• Predefined Macros:
• Undefining and Redefining Macros:
• Directives Within Macro Arguments:
• Macro Pitfalls:
Predefined Macros
• Standard Predefined Macros:
• Common Predefined Macros:
• System-specific Predefined Macros:
• C++ Named Operators:
Macro Pitfalls
• Misnesting:
• Operator Precedence Problems:
• Swallowing the Semicolon:
• Duplication of Side Effects:
• Self-Referential Macros:
• Argument Prescan:
• Newlines in Arguments:
Conditionals
• Conditional Uses:
• Conditional Syntax:
• Deleted Code:
Conditional Syntax
• Ifdef:
• If:
• Defined:
• Else:
• Elif:
Implementation Details
• Implementation-defined behavior:
• Implementation limits:
• Obsolete Features:
Obsolete Features
• Obsolete Features:

The C Preprocessor

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