Function pointer

Hello everyone,


In the following statements,

Code:

---

template <class R, class T> class 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

Quote:

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Originally Posted by George2

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?

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That first statement is weird. There must be some missing code.
Could it be some kind of declaration of function pointer? Still, it's missing ; at the end.

Quote:

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2. If yes, what is the parameter list of the function? Empty parameter list?

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Yes.

Quote:

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3. I doubt whether it is useful to define a function pointer with empty parameter list -- too restricted.

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Not always. You can use events for example, where you call back saying an event has finished or some such. Also useful when using dynamic linking of dlls. You get a function address dynamically from a dll, and call it using a function pointer.
Sometimes these functions don't take any arguments.

Quote:

---

Originally Posted by George2

Hello everyone,


In the following statements,

Code:

---

template <class R, class T> class 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.

Quote:

---

2. If yes, what is the parameter list of the function? Empty parameter list?

---

Correct.

Quote:

---

3. I doubt whether it is useful to define a function pointer with empty parameter list -- too restricted.

---

Yes, it's restricted in the sense that you can't pass in any parameters.

But some functions are fine without parameters. It's a typical case of "right tool for the job" - no point in adding parameters to a function if you don't actually need any. For example, this function may be to fetch an object R out of the T class, which only holds ONE R object - in which case, it's perfectly fine to do that without any parameters. Without a wider scope to understand the meaning of the code, it's impossible to say if it's "too restricted" or "just right".

--
Mats