Resolving ambiguous declarations (C++)


For the latest documentation on Visual Studio 2017 RC, see Visual Studio 2017 RC Documentation.

To perform explicit conversions from one type to another, you must use casts, specifying the desired type name. Some type casts result in syntactic ambiguity. The following function-style type cast is ambiguous:

char *aName( String( s ) );  

It is unclear whether it is a function declaration or an object declaration with a function-style cast as the initializer: It could declare a function returning type char * that takes one argument of type String, or it could declare the object aName and initialize it with the value of s cast to type String.

If a declaration can be considered a valid function declaration, it is treated as such. Only if it cannot possibly be a function declaration — that is, if it would be syntactically incorrect — is a statement examined to see if it is a function-style type cast. Therefore, the compiler considers the statement to be a declaration of a function and ignores the parentheses around the identifier s. On the other hand, the statements:

char *aName( (String)s );  


char *aName = String( s );  

are clearly declarations of objects, and a user-defined conversion from type String to type char * is invoked to perform the initialization of aName.

C++ Abstract Declarators