Help needed to understand "member function template"

[Aries Sun]

I am reading the book "Effective C++" Item 25 mentioned the following
code:
// a first cut at a class yielding NULL pointer objects
class NullClass {
public:
template<class T> // generates
operator T*() const { return 0; } // operator T* for
}; // all types T; each
// function returns
// the null pointer
const NullClass NULL; // NULL is an object of
// type NullClass
void f(int x); // same as we originally had
void f(string *p); // ditto
f(NULL); // fine, converts NULL to
// string*, then calls f(string*)
I have a hard time to understand the above, can anybody explain it to
me? thanks,

 

[Aries Sun]

my understanding is like this:
compiler would try to find out the right function for call f(NULL),
and will try f(int x), obviously this is not the right one, then will
try f(string *P), but this definition needs pointer so compiler will
try to call T* to do implicit conversion.

Am i right? thanks

 

[Barry]

my understanding is like this:
compiler would try to find out the right function for call f(NULL),
and will try f(int x), obviously this is not the right one, then will
try f(string *P), but this definition needs pointer so compiler will
try to call T* to do implicit conversion.

Am i right? thanks

you are right,
First, it find the exact match, but fail,
then find any other, to which NULL is convertible.

BTW, don't use NULL as an variable name in the program other than demo,
as it is a standard macro.

 

[Aries Sun]

thanks!

you are right,
First, it find the exact match, but fail,
then find any other, to which NULL is convertible.

BTW, don't use NULL as an variable name in the program other than demo,
as it is a standard macro.