Integer constant expressions
An integer constant is a value that is determined at compile time and cannot be changed at run time. An integer constant expression is an expression that is composed of constants and evaluated to a constant at compile time.
An integer constant expression is an expression that is
composed of only the following elements:
- literals
- enumerators
- const variables initialized with compile-time constant expressions
- static const data members initialized with compile-time constant expressions
- casts to integral types
- sizeof expressions, where the operand is not a variable length array
The sizeof operator applied to a variable length array type is evaluated at run time, and therefore is not a constant expression.
You must use an integer constant expression in the following
situations:
- In the subscript declarator as the description of an array bound.
- After the keyword case in a switch statement.
- In an enumerator, as the numeric value of an enumeration constant.
- In a bit-field width specifier.
- In the preprocessor #if statement. (Enumeration constants, address constants, and sizeof cannot be specified in a preprocessor #if statement.)
