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Use of typedef with Class Types

Use of the typedef specifier with class types is supported largely because of the ANSI C practice of declaring unnamed structures in typedef declarations. For example, many C programmers use the following:

// typedef_with_class_types1.cpp
// compile with: /c
typedef struct {   // Declare an unnamed structure and give it the
                   // typedef name POINT.
   unsigned x;
   unsigned y;

The advantage of such a declaration is that it enables declarations like:

POINT ptOrigin;

instead of:

struct point_t ptOrigin;

In C++, the difference between typedef names and real types (declared with the class, struct, union, and enum keywords) is more distinct. Although the C practice of declaring a nameless structure in a typedef statement still works, it provides no notational benefits as it does in C.

// typedef_with_class_types2.cpp
// compile with: /c /W1
typedef struct {
   int POINT();
   unsigned x;
   unsigned y;

The preceding example declares a class named POINT using the unnamed class typedef syntax. POINT is treated as a class name; however, the following restrictions apply to names introduced this way:

  • The name (the synonym) cannot appear after a class, struct, or union prefix.

  • The name cannot be used as constructor or destructor names within a class declaration.

In summary, this syntax does not provide any mechanism for inheritance, construction, or destruction.

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