Type Names In C++ - Tutorials Directory

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Type Names In C++

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Added: 13 June 2008 Views: 480

Path : Computers

Programming

C++

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In C, a common style of usage is to say:

        struct A {
                int x;
        };
        typedef struct A A;

after which A can be used as a type name to declare objects:

        void f()
        {
                A a;
        }

In C++, classes, structs, unions, and enum names are automatically type names, so you can say:

        struct A {
                int x;
        };

        void f()
        {
                A a;
        }

or:

        enum E {ee};

        void f()
        {
                E e;
        }

By using the typedef trick you can follow a style of programming in C somewhat like that used in C++.

But there is a quirk or two when using C++. Consider usage like:

        struct A {
                int x;
        };

        int A;

        void f()
        {
                A a;
        }

This is illegal because the int declaration A hides the struct declaration. The struct A can still be used, however, by specifying it via an "elaborated type specifier":

        struct A

The same applies to other type names:

        class A a;

        union U u;

        enum E e;

Taking advantage of this feature, that is, giving a class type and a variable or function the same name, isn't very good usage. It's supported for compatibility reasons with old C code; C puts structure tags (names) into a separate namespace, but C++ does not. Terms like "struct compatibility hack" and "1.5 namespace rule" are sometimes used to describe this feature.

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Type Names In C++
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