16 Library introduction [library]

16.4 Library-wide requirements [requirements]

16.4.5 Constraints on programs [constraints]

16.4.5.3 Reserved names [reserved.names]

16.4.5.3.1 General [reserved.names.general]

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The C++ standard library reserves the following kinds of names:
2
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If a program declares or defines a name in a context where it is reserved, other than as explicitly allowed by [library], its behavior is undefined.