Resolution of ambiguous statements (C++ only)

The C++ syntax does not disambiguate between expression statements and declaration statements. The ambiguity arises when an expression statement has a function-style cast as its left-most subexpression. (Note that, because C does not support function-style casts, this ambiguity does not occur in C programs.) If the statement can be interpreted both as a declaration and as an expression, the statement is interpreted as a declaration statement.

The following expressions disambiguate into expression statements because the ambiguous subexpression is followed by an assignment or an operator. type_spec in the expressions can be any type specifier:

type_spec(i)++;             // expression statement
type_spec(i,3)<<d;          // expression statement
type_spec(i)->l=24;         // expression statement

In the following examples, the ambiguity cannot be resolved syntactically, and the statements are interpreted as declarations. type_spec is any type specifier:

type_spec(*i)(int);         // declaration
type_spec(j)[5];            // declaration
type_spec(m) = { 1, 2 };    // declaration
type_spec(*k) (float(3));   // declaration

The last statement above causes a compile-time error because you cannot initialize a pointer with a float value.

Any ambiguous statement that is not resolved by the above rules is by default a declaration statement. All of the following are declaration statements:

type_spec(a);               // declaration
type_spec(*b)();            // declaration
type_spec(c)=23;            // declaration
type_spec(d),e,f,g=0;       // declaration
type_spec(h)(e,3);          // declaration

Related information

• Data objects and declarations
• Expressions and operators
• Function call expressions