Default Parameters.

Within C you could not provide default values for function parameters. Well, C++ has come to your rescue.

    #include <iostream.h>
    
    void Func( int one, int two=2, int three=3);
    
    main ()
    {
        Func(10, 20, 30);
        Func(10, 20);   // Let the last parm default
        Func(10);       // Just provide the required parm.
    }
    

    void Func( int one, int two, int three)
    {
        cout << "One   = " << one   << endl;
        cout << "Two   = " << two   << endl;
        cout << "Three = " << three << endl << endl;
    }

From this example, you can see that the prototype/function declaration gives default values for the second and third parameters. It is now down to the programmer calling the function to decide how many s/he wants to provide.

There are some basic rules that should be applied when using default parameter values.

• When a default is provided, all remaining parameters must be given defaults. There can not be any holes.
• Default values must be of the correct type.
• Defaults can be placed on the function prototype or the function definition. They can also be placed in both locations at the same time. I have been told its good practice to place them in the prototype only.

Examples:

See Also:

C References