Extended function parameters

Function parameter expansion

• It can provide a default value in the C ++ function declaration parameters 
• When the function call does not provide the value of the parameter, the default value

The default rule function parameters

• The default value of the parameter must be from right to left provided
• Use the default value when the function call, then the following parameters must use the default value

#include " stdio.h " 
int Mull ( int X = 2 );
 int the Add ( int X = . 1 , int Y = 2 , int Z = . 3 );
 // function parameter placeholder 
int FUNC ( int X, int )
{
        return x;
}
int main ()
{
        printf("%d\n", mull());       //x=2
        printf("%d\n", mull(3));      //x=3
        printf("%d\n", mull(-1));     //x=-1
        printf("%d\n", add());        //x=1,y=2,z=3
        printf("%d\n", add(0));       //x=0,y=2,z=3
        printf("%d\n", add(2,3));     //x=2,y=3,z=3
        printf("%d\n", add(4,5,6));   //x=4,y=5,z=6
        func(1,2);
        return 0;
}
int mull(int x)
{
        return x*x;
}
you add ( you get, you y, you z)
{
        return x + y + z;
}

Placeholder function parameter

• It may be provided as a function of positional parameters in C ++
• Placeholder parameters only parameter type declaration, but did not declare the parameter name
• Under normal circumstances, can not be used in the functions that parameter placeholder

Meaning placeholder function parameter

• Placeholder parameters used in conjunction with default parameters
• Not compatible with standard programs written in C language may arise

In the C language void func (); and a void func (void); inequivalent

void func in the C ++ language (); and a void func (void); Equivalent