C++ Constant Expressions
C++ requires constant expressions — expressions that evaluate to a constant — for declarations of:
- Array bounds
- Selectors in case statements
- Bit-field length specification
- Enumeration initializers
- constant-expression :
The only operands that are legal in constant expressions are:
- Enumeration constants
- Values declared as const that are initialized with constant expressions
- sizeof expressions
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.