| title | C++ Constant Expressions | Microsoft Docs | |||||||||||||
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| ms.date | 11/04/2016 | |||||||||||||
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| ms.topic | language-reference | |||||||||||||
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| ms.assetid | b07245a5-4c21-4589-b503-e6ffd631996f | |||||||||||||
| caps.latest.revision | 8 | |||||||||||||
| author | mikeblome | |||||||||||||
| ms.author | mblome | |||||||||||||
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A constant value is one that doesn't change. C++ provides two keywords to enable you to express the intent that an object is not intended to be modified, and to enforce that intent.
C++ requires constant expressions — expressions that evaluate to a constant — for declarations of:
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Array bounds
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Selectors in case statements
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Bit-field length specification
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Enumeration initializers
The only operands that are legal in constant expressions are:
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Literals
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Enumeration constants
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Values declared as const that are initialized with constant expressions
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sizeofexpressions
Nonintegral constants must be converted (either explicitly or implicitly) to integral types to be legal in a constant expression. Therefore, the following code is legal:
const double Size = 11.0;
char chArray[(int)Size];
Explicit conversions to integral types are legal in constant expressions; all other types and derived types are illegal except when used as operands to the sizeof operator.
The comma operator and assignment operators cannot be used in constant expressions.