The topic you requested is included in another documentation set. For convenience, it's displayed below. Choose Switch to see the topic in its original location.

Anonymous Class Types


The latest version of this topic can be found at Anonymous Class Types.

Classes can be anonymous — that is, they can be declared without an identifier. This is useful when you replace a class name with a typedef name, as in the following:

typedef struct  
    unsigned x;  
    unsigned y;  
} POINT;  

System_CAPS_ICON_note.jpg Note

The use of anonymous classes shown in the previous example is useful for preserving compatibility with existing C code. In some C code, the use of typedef in conjunction with anonymous structures is prevalent.

Anonymous classes are also useful when you want a reference to a class member to appear as though it were not contained in a separate class, as in the following:

struct PTValue  
    POINT ptLoc;  
        int  iValue;  
        long lValue;  
PTValue ptv;  

In the preceding code, iValue can be accessed using the object member-selection operator (.) as follows:

int i = ptv.iValue;  

Anonymous classes are subject to certain restrictions. (For more information about anonymous unions, see Unions.) Anonymous classes:

  • Cannot have a constructor or destructor.

  • Cannot be passed as arguments to functions (unless type checking is defeated using ellipses).

  • Cannot be returned as return values from functions.

Microsoft Specific

A Microsoft C extension allows you to declare a structure variable within another structure without giving it a name. These nested structures are called anonymous structures. C++ does not allow anonymous structures.

You can access the members of an anonymous structure as if they were members in the containing structure.

// anonymous_structures.c  
#include <stdio.h>  
struct phone  
    int  areacode;  
    long number;  
struct person  
    char   name[30];  
    char   gender;  
    int    age;  
    int    weight;  
    struct phone;    // Anonymous structure; no name needed  
} Jim;  
int main()  
    Jim.number = 1234567;  
    printf_s("%d\n", Jim.number);     
//Output: 1234567  

END Microsoft Specific

(NOTINBUILD) Defining Class Types