The C Preprocessor

Table of Contents

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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.

• 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:  



• Stringification:  



• 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:  



• Differences from previous versions:  



Obsolete Features


• Obsolete Features:  






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A GNU Manual



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