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#ifndef directive

#ifndef directive Tests whether a macro is undefined 
#ifndef identifier

The #ifndef directive begins a region of conditional compilation. It takes a single identifier as an argument and is equivalent to #if not defined identifier.

See Also

defined operator, #if directive, #ifdef directive



    		Chapter 1. Language Basics
    		Chapter 2. Declarations
    		Chapter 3. Expressions
    		Chapter 4. Statements
    		Chapter 5. Functions
    		Chapter 6. Classes
    		Chapter 7. Templates
    		Chapter 8. Standard Library
    		Chapter 9. Input and Output
    		Chapter 10. Containers, Iterators, and Algorithms
    		Chapter 11. Preprocessor Reference
    		# operator and directive
    		## operator
    		#define directive
    		defined operator
    		#elif directive
    		#else directive
    		#endif directive
    		#error directive
    		#if directive
    		#ifdef directive
    		#ifndef directive
    		#include directive
    		#line directive
    		#pragma directive
    		#undef directive
    		Chapter 12. Language Reference
    		Chapter 13. Library Reference
    		Appendix A. Compiler Extensions
    		Appendix B. Projects
    		Glossary