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I think what I am looking for is a "nested function" which C++ doesn't

officially

support. Is the following workaround possible?





1. create a pointer to a function of type void fun ()

2. allocate memory for it

3. populate memory so newly created function does what I want

4. return pointer to said function



thx, -Alex


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alexl wrote:

Why do you think you want nested functions?



Typically, the only things that nested functions add are:



1. more limited scope of name visibility.

2. access to "up level" local variables (if c() is in b() which is in a(),

c() can access b()'s local variables as well as a()'s).



Use of classes instead of free functions more or less supplies 1. 2 can be

accomplished manually by passing references to the required up-level

variables.



What is it that you're trying to achieve?



-cd





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Thanks! Trying to accomplish the following. Should print "it worked."



typedef void(*ptf)();



class Hello {



void caller(){

ptf =cplusplusbind(this, m_callback);

..

call_fun_indirectly(ptf);

}



void m_callback () {

cout << "it worked!\n";

}



};



int main(int argc, char* argv[])

{

Hello h;

h.caller();

return 0;



}



ptf cplusplusbind (class T, T::*) {



return (/* do magic */ );



-

alexl wrote:

Boost helps here:



boost::function<void()>ptf;



class Hello {

void caller(){

ptf = boost::bind(&Hello::m_callback, this);

..

ptf();

}



void m_callback () {

cout << "it worked!\n";

}

};



int main(int argc, char* argv[])

{

Hello h;

h.caller();

return 0;

}



See boost.function and boost.bind (both being added to library extension

that is being added to standard C++), at www.boost.org.



Tom

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alexl wrote:

Actually, you can put a function within a function, but not in the

normal sense. Try something like this:



void MyClass::SomeFunction()

{

struct Inner

{

static int InnerWorkings(int i)

{

return i * 4;

}

};



printf("Inner function call result: %d\n", Inner::InnerWorkings(5));

}



You would have to wonder why one would do this because for the

most part you shouldn't need to. However on a few rare occasions

it does come in handy.



Murrgon

-

thanks!



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"Carl Daniel [VC++ MVP]" <cpdaniel_remove_this_and_nospam@mvps.org.nospam>

wrote in message>

Indeed. The common case where I want nested functions is in recursive

functions, to supply the outer case. Typically, a recursive function may act

on some state, and either we pass it down the stack every time or create an

outer function which it can access. Generally now I use an anonymous

namespace to deal with this, but this still is polluting the namespace, be

it only by one name.



I *think* I have a reasonable argument that nested functions are just

anonymous classes (in the Java sense) that have names, but I'm not entirely

sure.



S.



"Whereof one cannot speak, thereof one must be silent." -- Wittgenstein.

"If you don't know, shut up." -- The wife.





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