NGWS SDK Documentation  

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7.6.8 Cast expressions

A cast-expression is used to explicitly convert an expression to a given type.

cast-expression:
( type ) unary-expression

A cast-expression of the form (T)E, where T is a type and E is a unary-expression, performs an explicit conversion (§6.2) of the value of E to type T. If no explicit conversion exists from the type of E to T, an error occurs. Otherwise, the result is the value produced by the explicit conversion. The result is always classified as a value, even if E denotes a variable.

The grammar for a cast-expression leads to certain syntactic ambiguities. For example, the expression (x)–y could either be interpreted as a cast-expression (a cast of –y to type x) or as an additive-expression combined with a parenthesized-expression (which computes the value x y).

To resolve cast-expression ambiguities, the following rule exists: A sequence of one or more tokens (§2.4.6) enclosed in parentheses is considered the start of a cast-expression only if at least one of the following are true:

The above rules mean that only if the construct is unambiguously a cast-expression is it considered a cast-expression.

The term "correct grammar" above means only that the sequence of tokens must conform to the particular grammatical production. It specifically does not consider the actual meaning of any constituent identifiers. For example, if x and y are identifiers, then x.y is correct grammar for a type, even if x.y doesn’t actually denote a type.

From the disambiguation rules it follows that, if x and y are identifiers, (x)y, (x)(y), and (x)(-y) are cast-expressions, but (x)-y is not, even if x identifies a type. However, if x is a keyword that identifies a predefined type (such as int), then all four forms are cast-expressions (because such a keyword could not possibly be an expression by itself).