Hello everyone,
In the following statements, -
template <class R, class Tclass mem_fun_t : public unary_function
-
<T*, R>
-
-
{
-
-
R (T::*pmf)()
-
....
-
}
-
1. I think pmf is a type of function pointer, the return type of the
function is R and the function is a member function of type (class) T.
Is my understanding correct?
2. If yes, what is the parameter list of the function? Empty parameter
list?
3. I doubt whether it is useful to define a function pointer with
empty parameter list -- too restricted.
thanks in advance,
George 3 1726
George2 wrote:
Hello everyone,
In the following statements,
-
template <class R, class Tclass mem_fun_t : public unary_function
-
<T*, R>
-
{
-
R (T::*pmf)()
-
...
-
}
-
1. I think pmf is a type of function pointer,
With a semicolon added to the end of that line, pmf would be the name of a
member variable of mem_fun_t.
the return type of the function is R and the function is a member function
of type (class) T.
Yes.
2. If yes, what is the parameter list of the function? Empty parameter
list?
Yes.
3. I doubt whether it is useful to define a function pointer with
empty parameter list -- too restricted.
Well, it is restricted to functions that have exactly 0 parameters. If you
defined a pointer to function with 10 parameters, it would be restricted to
functions that take exactly 10 parameters.
George2 a écrit :
Hello everyone,
In the following statements,
-
template <class R, class Tclass mem_fun_t : public unary_function
-
<T*, R>
-
{
-
R (T::*pmf)()
-
...
-
}
-
1. I think pmf is a type of function pointer, the return type of the
function is R and the function is a member function of type (class) T.
Is my understanding correct?
yes.
In brief it iss a pointer on a member fucntion of class T.
>
2. If yes, what is the parameter list of the function? Empty parameter
list?
Yes. No parameters.
>
3. I doubt whether it is useful to define a function pointer with
empty parameter list -- too restricted.
It is useful if you want to call a method of a class that takes no
parameters.
struct foo
{
static int gcounter=0;
foo(){id_=gcoun ter++;}
void bar(){std::cout <<"My id is "<<id_<<std::en dl;}
int id_;
};
std::vector<foo v(10);
std::for_each(v .begin(),v.end( ),std::mem_fun_ ref(&foo::bar)) ;
Of course, you could put parameters in a class and make it a wrapper
class of a more elaborate functor.
Another example from SGI:
struct B {
virtual void print() = 0;
};
struct D1 : public B {
void print() { cout << "I'm a D1" << endl; }
};
struct D2 : public B {
void print() { cout << "I'm a D2" << endl; }
};
int main()
{
vector<B*V;
V.push_back(new D1);
V.push_back(new D2);
V.push_back(new D2);
V.push_back(new D1);
for_each(V.begi n(), V.end(), mem_fun(&B::pri nt));
}
Michael
On 2007-12-10 06:48:11 -0500, George2 <ge************ *@yahoo.comsaid :
Hello everyone,
In the following statements,
-
template <class R, class Tclass mem_fun_t : public unary_function
-
<T*, R>
-
{
-
R (T::*pmf)()
-
...
-
}
-
1. I think pmf is a type of function pointer,
No. It's a pointer to member function, which is not at all like a
pointer to (non-member) function.
the return type of the
function is R and the function is a member function of type (class) T.
Is my understanding correct?
Right.
>
2. If yes, what is the parameter list of the function? Empty parameter
list?
Yes.
>
3. I doubt whether it is useful to define a function pointer with
empty parameter list -- too restricted.
Read about what mem_fun_t is used for. The definition of pmf is exactly
what's needed.
--
Pete
Roundhouse Consulting, Ltd. ( www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
( www.petebecker.com/tr1book) This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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