Nested functions in C++

[A]

Hi,

How do you make use of nested functions in C++? I realize in C++ that
everything must be declared first in a header file before implementation in
a .cpp file. I tried to nest a method prototype in another prototype but
seems pointless. Can someone please write a short, simple, and concise
skeleton code of how to use nested functions?

class Foo
{
private:
int a;
int b;

public:
void funcA();
void funcB(); // seems pointless
}

void Foo:: funcA()
{
this->funcB;
void Foo::funcB()
{...}
}
//error: local method problem

any help appreciated.

Regards
reuytrt


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[Dave Theese]

Re: Nested functions in C++


"A" <A@iprimus.com. au> wrote in message
news:3f6d37b3_1 @news.iprimus.c om.au...[color=blue]
> Hi,
>
> How do you make use of nested functions in C++? I realize in C++ that
> everything must be declared first in a header file before implementation[/color]
in[color=blue]
> a .cpp file. I tried to nest a method prototype in another prototype but
> seems pointless. Can someone please write a short, simple, and concise
> skeleton code of how to use nested functions?
>
> class Foo
> {
> private:
> int a;
> int b;
>
> public:
> void funcA();
> void funcB(); // seems pointless
> }
>
> void Foo:: funcA()
> {
> this->funcB;
> void Foo::funcB()
> {...}
> }
> //error: local method problem
>
> any help appreciated.
>
> Regards
> reuytrt
>
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.518 / Virus Database: 316 - Release Date: 11/09/2003
>
>[/color]

Functions may not be nested in C++. Nor is it *required* that declarations
appear in a header file, but good design generally dictates that interface
and implementation be separated.

Hope this helps!

[John Tsiombikas (Nuclear / the Lab)]

Re: Nested functions in C++

A wrote:[color=blue]
> Hi,
>
> How do you make use of nested functions in C++?[/color]

you can't...

-- Nuclear / the Lab --

[Alf P. Steinbach]

Re: Nested functions in C++

On Sun, 21 Sep 2003 15:01:30 +0930, "A" <A@iprimus.com. au> wrote:
[color=blue]
>How do you make use of nested functions in C++?[/color]

Before you can use them you must have them.

C++ does not support nested function à la Pascal, but does support a
limited form of local classes (nested in functions).

You can use local classes to achieve logical nesting, but a member
function of a local class doesn't have access to the arguments and
local variables of the enclosing function unless you provide such
access yourself, e.g. via reference constructor arguments.


[color=blue]
>I realize in C++ that everything must be declared first in a header
>file before implementation in a .cpp file.[/color]

That is incorrect; the C++ standard does not even mention files.

[color=blue]
>I tried to nest a method prototype in another prototype but
>seems pointless. Can someone please write a short, simple, and concise
>skeleton code of how to use nested functions?
>
>class Foo
>{
> private:
> int a;
> int b;
>
> public:
> void funcA();
> void funcB(); // seems pointless
>}[/color]

It is, indentation is not equal to logical nesting.



[color=blue]
>void Foo:: funcA()
>{
> this->funcB;
> void Foo::funcB()
> {...}
>}
>//error: local method problem
>
>any help appreciated.[/color]

The best you can do is forget it, then investigate the issue anew
in a few years time.

[Ying Yang]

Re: Nested functions in C++


"Dave Theese" <cheeser_1998@y ahoo.com> wrote in message
news:dRabb.558$ La.517@fed1read 02...[color=blue]
>
> "A" <A@iprimus.com. au> wrote in message
> news:3f6d37b3_1 @news.iprimus.c om.au...[color=green]
> > Hi,
> >
> > How do you make use of nested functions in C++? I realize in C++ that
> > everything must be declared first in a header file before implementation[/color]
> in[color=green]
> > a .cpp file. I tried to nest a method prototype in another prototype but
> > seems pointless. Can someone please write a short, simple, and concise
> > skeleton code of how to use nested functions?
> >
> > class Foo
> > {
> > private:
> > int a;
> > int b;
> >
> > public:
> > void funcA();
> > void funcB(); // seems pointless
> > }
> >
> > void Foo:: funcA()
> > {
> > this->funcB;
> > void Foo::funcB()
> > {...}
> > }
> > //error: local method problem
> >
> > any help appreciated.
> >
> > Regards
> > reuytrt[/color]
>
> Functions may not be nested in C++. Nor is it *required* that[/color]
declarations[color=blue]
> appear in a header file, but good design generally dictates that interface
> and implementation be separated.
>
> Hope this helps![/color]


Surely there must be a solution to this problem. The reason i wanted to do
this is because i want to be able to group related functions together. For
example a function that calls another related function to solve a problem
(this can be seen in indirect recursion calls).


Regards
ewrewrwer


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[Bronek Kozicki]

Re: Nested functions in C++

On Sun, 21 Sep 2003 18:53:06 +0930, Ying Yang wrote:[color=blue]
> Surely there must be a solution to this problem. The reason i wanted to do
> this is because i want to be able to group related functions together. For[/color]

This is exactly why C++ was invented - to group functions together into
classes. Look at following (incorrect) code:

int f(int i)
{
int j = i + 1;
int a() // local function is invalid!
{
return j * i;
};

return a() + i;
}

it won't work, but you can use class instead:

class f {
const int& i; // variables shared between all ...
int j; // ... functions grouped into class
int ret; // return value
int a() // "internal" function
{
return j * i;
}
public:
f(const int& arg_i) : i(arg_i), j(i + 1)
{
ret = a() + i;
}

operator int() {return ret;}
// bonus: alternate return type from function object
operator std::string() {return "hi!";}
};

You may call your function object simply creating it:
int r = f(3);

you may also retrieve its "alternate" return value:
std::string q = f(4);

regards


B.

[Sektor van Skijlen]

Re: Re: Nested functions in C++

Bronek Kozicki <brok@rubikon.p l> wrote:
# Look at following (incorrect) code:

# int f(int i)
# {
# int j = i + 1;
# int a() // local function is invalid!
# {
# return j * i;
# };
#
# return a() + i;
# }

# it won't work, but you can use class instead:

Maybe, but this will not replace the local (or nested, as you like) functions.
It just tries to help with the problem they deal with.

Local functions have an access to the local environment of the parent function.
You cannot achieve this in C++. To have local functions you would like also
to have a mechanism of closures, as it is done for example in boost::phoenix.

# You may call your function object simply creating it:
# int r = f(3);

# you may also retrieve its "alternate" return value:
# std::string q = f(4);

Fine, but you still have to pass arguments to such a "functionat e".
You have declared a local function in this (incorrect) code before,
which does not need to be passed an argument; it takes the value from
the local environment from the parent function. You cannot simulate
this anyhow in C++ (unless you directly pass a "closure" as an argument :).

Regards,


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