Function returning a function pointer?

[Protoman]

How would you write a function returning a function pointer and why
would you need to do this? Is it:

int(*)(int&) fn(int& arg);

Thanks!!!

 

[benben]

How would you write a function returning a function pointer and why
would you need to do this?

There are many reason why one function would return a function pointer.
The most obvious are:

- to give user a channel to access futher information
- to give follow up which can be chain-invoked

Is it:

int(*)(int&) fn(int& arg);

Thanks!!!

The correct declaration is:

int (*fn(int& arg))(int&);

If this seems cryptic, read it outside in:

-the return type is a pointer to int(int&) therefore:

int (* [...])(int&);

-the [...] is the function fn itself therefore:

int (*
fn(int& arg)
)(int& arg);

Alternatively, you can typedef the return type in advance:

typedef int(*fn_ptr)(int&);
fn_ptr fn(int& arg);

Regards,
Ben

 

[John Carson]

How would you write a function returning a function pointer and why
would you need to do this? Is it:

int(*)(int&) fn(int& arg);

Thanks!!!

Given a function

int foo(int &x)
{
++x;
return x;
}

a function that takes an int reference parameter arg and will return a
pointer to foo takes the form

int (*fn(int& arg))(int &)
{
return &foo; // the & is optional
}

However, you will give yourself less brain strain if you do it this way:

typedef int (*fnptr)(int&);

fnptr fn(int& arg)
{
return &foo;
}

As for why you would need to do this, perhaps fn would select the
appropriate function pointer the program needs to use, based on the
calculations it does with arg.

 

[Protoman]

Can I use such a construct to do currying?

 

[Alf P. Steinbach]

* Protoman:

How would you write a function returning a function pointer and why
would you need to do this? Is it:

int(*)(int&) fn(int& arg);

Thanks!!!

See the FAQ about H O M E W O R K.

 

[Protoman]

THIS IS NOT HOMEWORK!!!!!!! I AM A COLLEGE MED STUDENT!!!! THIS IS A
BLOODY HOBBY OF MINE!!!! NOTHING I EVER POST IS HOMEWORK!!!!!

 

[Neelesh Bodas]

Can I use such a construct to do currying?

You can simulate currying using function pointers

Eg f x y = x is a curried function. It can be seen as a function
which takes an object of type T and returns a function (poiner) which
takes an object of type U and returns an object of type T. In pseudo
code, it becomes T (*f (T))(U)

HTH

 

[Protoman]

You can simulate currying using function pointers

Eg f x y = x is a curried function. It can be seen as a function
which takes an object of type T and returns a function (poiner) which
takes an object of type U and returns an object of type T. In pseudo
code, it becomes T (*f (T))(U)

HTH

I can't follow that; could you put that into C++ code and show me an
example? Thanks!!!

 

[Alf P. Steinbach]

* benben:

I believe C++ declaration syntax is more than what people would struggle
with as homework.

"and why would you need it"

 

[benben]

See the FAQ about H O M E W O R K.

I believe C++ declaration syntax is more than what people would struggle
with as homework.

Ben

 

[benben]

You can simulate currying using function pointers

I believe function objects would be more appropriate as they can hold a
state (the extra argument)

As for the OP:

std::bind1st, std::bind2nd, mem_fun and mem_fun_ref are what I believe
good examples of currying right out from the standard library. The
latter two curry the hidden *this pointer.

Ben

 

[Neelesh Bodas]

I believe function objects would be more appropriate as they can hold a
state (the extra argument)

Yes. You are right. I was trying hard to simulate currying using plane
old functions but could not get how to do that

int (*fp)(char);
fp f(int x)
{
//somehow create a function and store this x in it so that when that
function will be invoked later in the code we could get back this x.
// could be done with global variables but would require a fresh global
variable for every invocation of f.
// best alternative is to use function objects
}

 

[red floyd]

THIS IS NOT HOMEWORK!!!!!!! I AM A COLLEGE MED STUDENT!!!! THIS IS A
BLOODY HOBBY OF MINE!!!! NOTHING I EVER POST IS HOMEWORK!!!!!

I thought you were a JPL Rocket Scientist?

 

[John Carson]

I thought you were a JPL Rocket Scientist?

I remember now. Protoman is a liar who just tells one story after another. I
had him in my blocked senders list, but I haven't transferred that list over
to my new computer. Oh well, I have corrected that now, at least as far as
Protoman is concerned.

 

[Protoman]

No, this is the *truth*. I've just finished pre-med at UCLA and I'm
entering Harvard med. Now, lets get back on topic. I DON'T LIE
ANYMORE!!!! Thank you.