C++ operator++ overloading, prefix vs postfix

[chingkui]

I have seen how people implement the prefix and postfix ++ overloading, which are as follow:

Number& operator++ () // prefix ++
{
// Do work on this.
return *this;
}

Number operator++ (int) // postfix ++
{
Number result(*this); // make a copy for result
++(*this); // Now use the prefix version to do the work
return result; // return the copy (the old) value.
}

What I don't understand is:
When you call ++m1 and m2++, how does the machine know it should call Number& operator++ () for m1 and Number operator++ (int) for m2? I look at it and think about it for a long time, but I still couldn't tell from the syntax how it is done. Did I miss something obvious?

 

[D H]

The prefix and postfix versions have different signatures. The (int) argument to the postfix version of operator++ is a dummy argument. It's a built-in feature of the language specification that ++m1 translates to a call to operator++(), m2++ to a call to operator++(int).