C默认功能参数

我想实现这个目标：

- second parameter by default set to first argument

就像是：

int foo (int a,int b = a);

但是怎么做呢？

非常感谢！

解决方法

这是禁止的：

8.3.6默认参数[dcl.fct.default]

9) Default arguments are evaluated each time the function is called.
The order of evaluation of function arguments is unspecified.
Consequently,parameters of a function shall not be used in default
argument expressions,even if they are not evaluated. Parameters of a
function declared before a default argument expression are in scope
and can hide namespace and class member names. [ Example:

int a;

int f(int a,int b = a); / / error: parameter a

/ / used as default argument

typedef int I;

int g( float I,int b = I (2)); / / error: parameter I found

int h(int a,int b = sizeof (a )); / / error,parameter a used

/ / in default argument

—end example ]

另一种方法是重载：

int foo(int a,int b);

int foo(int a)
{
   return foo(a,a);
}