Named variable in a list?

[Jonathan.Fillion]

Ok, I have a simple problem and I might just be blind and not see the
(possibly simple) solution to it. I want to declare variables while
adding them to a list simultaneously. What I want to do is something
like that:

int a, b, c;
int list[] = {&a, &b, &c};

But I only want to declare 'a', 'b' and 'c' once (they're declared 2
time here, one for the instance and one for the pointer in the list).
Now I figure it's possible to do that using a macro, but I just can't
figure out how, ie:

declare(list, int, a);
declare(list, int, b);
declare(list, int, c);

declare_instanc es();
declare_list_po inters();

You'd need some kind of way to store data in temporary memory with
macros. Is there something standard for doing that? (or a totally
different approach I haven't seen).

Thnx

[Puppet_Sock]

Jo************* *@gmail.com wrote:

Ok, I have a simple problem and I might just be blind and not see the
(possibly simple) solution to it. I want to declare variables while
adding them to a list simultaneously. What I want to do is something
like that:

int a, b, c;
int list[] = {&a, &b, &c};

But I only want to declare 'a', 'b' and 'c' once (they're declared 2
time here, one for the instance and one for the pointer in the list).

Um. I don't think that's quite right. This is going to give you
compiler
diagnostics about converting from int * to int. You should change this
to one of the following.

int * list[] = {&a, &b, &c};
int list[] = {a,b,c};

Though, with the second, you want to initialize a, b, and c before
you use the values to fill in the array.

Also, it does not declare a, b, and c twice. Assuming it actually
worked, the declaration of a is on the line

int a,b,c;

and nowhere else.

Also, "list" is a poor name for an array.

Now I figure it's possible to do that using a macro, but I just can't
figure out how, ie:

declare(list, int, a);
declare(list, int, b);
declare(list, int, c);

declare_instanc es();
declare_list_po inters();

You'd need some kind of way to store data in temporary memory with
macros. Is there something standard for doing that? (or a totally
different approach I haven't seen).

It's really not clear what it is that you want to do that would not be
done by cleaning up your original example. Can you explain differently
why the original would not be acceptable?
Socks

[Alan Johnson]

Jo************* *@gmail.com wrote:

Ok, I have a simple problem and I might just be blind and not see the
(possibly simple) solution to it. I want to declare variables while
adding them to a list simultaneously. What I want to do is something
like that:

int a, b, c;
int list[] = {&a, &b, &c};

You can't put pointers to ints in an array of ints.
Either:
int a, b, c ;
int * list[] {&a, &b, &c} ;

or:
int list[3] ;

>
But I only want to declare 'a', 'b' and 'c' once (they're declared 2
time here, one for the instance and one for the pointer in the list).
Now I figure it's possible to do that using a macro, but I just can't
figure out how, ie:

declare(list, int, a);
declare(list, int, b);
declare(list, int, c);

declare_instanc es();
declare_list_po inters();

You'd need some kind of way to store data in temporary memory with
macros. Is there something standard for doing that? (or a totally
different approach I haven't seen).

Thnx

"Macros are evil."

It looks like you are trying to do something like:

{
int a ;
list[0] = &a ;
}

But then when that scope exits your pointer is no longer valid anyway,
so trying to use it is undefined behavior.

Somewhat unrelated, since if I'm right about what you are trying to do,
you shouldn't use this anyway, but if you need to create temporaries in
a macro, a common trick is something like:
#define MYMACRO \
do \
{ \
} while(0)

The do/while(0) introduces a scope you can put stuff in, and also is
syntactically correct if you put a semicolon after a use of your macro.

--
Alan Johnson

[Jonathan.Fillion]

Ok, my mistake I meant:

int * list[] = {&a, &b, &c};

in the original post (google groups don't give compiler warnings duh).

I know 'a' does get declared only once; all I'm saying is if you want
to add something you gotta type it twice (declaration and adding to the
list). And uhm, list being a poor name for an array, I couldn't care
less; this is just a dumb example.

Hope this clarifies the thing.

Puppet_Sock wrote:

Jo************* *@gmail.com wrote:

Ok, I have a simple problem and I might just be blind and not see the
(possibly simple) solution to it. I want to declare variables while
adding them to a list simultaneously. What I want to do is something
like that:

int a, b, c;
int list[] = {&a, &b, &c};

But I only want to declare 'a', 'b' and 'c' once (they're declared 2
time here, one for the instance and one for the pointer in the list).

Um. I don't think that's quite right. This is going to give you
compiler
diagnostics about converting from int * to int. You should change this
to one of the following.

int * list[] = {&a, &b, &c};
int list[] = {a,b,c};

Though, with the second, you want to initialize a, b, and c before
you use the values to fill in the array.

Also, it does not declare a, b, and c twice. Assuming it actually
worked, the declaration of a is on the line

int a,b,c;

and nowhere else.

Also, "list" is a poor name for an array.

Now I figure it's possible to do that using a macro, but I just can't
figure out how, ie:

declare(list, int, a);
declare(list, int, b);
declare(list, int, c);

declare_instanc es();
declare_list_po inters();

You'd need some kind of way to store data in temporary memory with
macros. Is there something standard for doing that? (or a totally
different approach I haven't seen).

It's really not clear what it is that you want to do that would not be
done by cleaning up your original example. Can you explain differently
why the original would not be acceptable?
Socks

[Frederick Gotham]

posted:

I want to declare variables while
adding them to a list simultaneously.

Are you trying to achieve something like the following?

(Written sloppily with haste, may contain a bug or two:)

#define nullptr 0 /* Until the next Standard */

#include <iostream>
using std::cout;

template<class T>
struct LinkedPointer {
T *p;
LinkedPointer *pnext;
};

class Chain {
private:
int first_int;
LinkedPointer<i ntfirst_link;

public:

Chain() : first_int(-999)
{
first_link.p = &first_int;
first_link.pnex t = nullptr;
}

Chain &Register(in t &var)
{
/* This algorithm is inefficient, but it does the trick */

LinkedPointer<i nt**p;

for(p = &first_link.pne xt; *p; p = &(*p)->pnext) /* No body */;
/* This loop brings it until the next nullptr */

*p = new LinkedPointer<i nt>;

(*p)->p = &var;
(*p)->pnext = nullptr;

return *this;
}

void PrintAllRegiste red() const
{
cout << first_int << '\n';

for(LinkedPoint er<int*const*p = &first_link.pne xt; *p; p = &
(*p)->pnext)
cout << *(*p)->p << '\n';
}
};

Chain global_chain;

void SomeFunc()
{
int static i = 67;

global_chain.Re gister(i);
}

int main()
{
int a = 5, b = 22, c = 656;

global_chain.Re gister(a).Regis ter(b).Register (c);

SomeFunc();

int &d = *new int(13);

global_chain.Re gister(d);

global_chain.Pr intAllRegistere d();

delete &d;
}

--

Frederick Gotham

[Alan Johnson]

Jo************* *@gmail.com wrote:

Puppet_Sock wrote:

Jo************* *@gmail.com wrote:

Ok, I have a simple problem and I might just be blind and not see the
(possibly simple) solution to it. I want to declare variables while
adding them to a list simultaneously. What I want to do is something
like that:
>
int a, b, c;
int list[] = {&a, &b, &c};
>
But I only want to declare 'a', 'b' and 'c' once (they're declared 2
time here, one for the instance and one for the pointer in the list).

Um. I don't think that's quite right. This is going to give you
compiler
diagnostics about converting from int * to int. You should change this
to one of the following.

int * list[] = {&a, &b, &c};
int list[] = {a,b,c};

Though, with the second, you want to initialize a, b, and c before
you use the values to fill in the array.

Also, it does not declare a, b, and c twice. Assuming it actually
worked, the declaration of a is on the line

int a,b,c;

and nowhere else.

Also, "list" is a poor name for an array.

Now I figure it's possible to do that using a macro, but I just can't
figure out how, ie:
>
declare(list, int, a);
declare(list, int, b);
declare(list, int, c);
>
declare_instanc es();
declare_list_po inters();
>
You'd need some kind of way to store data in temporary memory with
macros. Is there something standard for doing that? (or a totally
different approach I haven't seen).

It's really not clear what it is that you want to do that would not be
done by cleaning up your original example. Can you explain differently
why the original would not be acceptable?
Socks

Ok, my mistake I meant:

int * list[] = {&a, &b, &c};

in the original post (google groups don't give compiler warnings duh).

I know 'a' does get declared only once; all I'm saying is if you want
to add something you gotta type it twice (declaration and adding to the
list). And uhm, list being a poor name for an array, I couldn't care
less; this is just a dumb example.

Hope this clarifies the thing.

Please don't top post.
http://www.parashift.com/c++-faq-lit...t.html#faq-5.4

Perhaps it would help if you explained what problem you are trying to
solve. Creating a bunch of ints and then putting pointers to them in
an array doesn't seem particularly useful. If you want an array of
ints just declare one. If, perhaps, you want a list, look into
std::list or std::vector.

--
Alan Johnson

[Frederick Gotham]

Frederick Gotham posted:

void PrintAllRegiste red() const
{
cout << first_int << '\n';

for(LinkedPoint er<int*const*p = &first_link.pne xt; ...

LinkedPointer<i ntconst *const *p

--

Frederick Gotham

[Jonathan.Fillion]

Frederick Gotham wrote:

Frederick Gotham posted:

void PrintAllRegiste red() const
{
cout << first_int << '\n';

for(LinkedPoint er<int*const*p = &first_link.pne xt; ...

LinkedPointer<i ntconst *const *p

--

Frederick Gotham

Uhm, look, what I'm asking is simple. I want to do this:

int a, b;
list.add(&a); list.add(&b);

with something like this:

declare_and_add (a);
declare_and_add (b);

Now, fill in the blank for 'declare_and_ad d' (either with a #define,
template, whatever). Don't ask about the particular context -- this is
a totally out of context, _simple_ problem (not that the solution is).

[Frederick Gotham]

Jonathan posted:

Uhm, look, what I'm asking is simple.

Magnificient tone of voice. I think I'll be sadistic and not help you.

I want to do this:

int a, b;
list.add(&a); list.add(&b);

with something like this:

declare_and_add (a);
declare_and_add (b);

Now, fill in the blank for 'declare_and_ad d'

Do I've to have this done for you by 5pm on Thursday?

(either with a #define, template, whatever).

#define JonathanFillion Arrogant Asshole

or perhaps:

struct JonathanFillion {};

template<class ArrogantAsshole >
void TempFunc()
{

}

void (&Func)() = TempFunc<Jonath anFillion>;

Don't ask about the particular context -- this is
a totally out of context, _simple_ problem (not that the solution is).

The solution is *extremely* simple. Pity I'm too sadistic to show you how
macros work.

--

Frederick Gotham

[Jonathan.Fillion]

Frederick Gotham wrote:

Jonathan posted:

Uhm, look, what I'm asking is simple.

Magnificient tone of voice. I think I'll be sadistic and not help you.

I want to do this:

int a, b;
list.add(&a); list.add(&b);

with something like this:

declare_and_add (a);
declare_and_add (b);

Now, fill in the blank for 'declare_and_ad d'

Do I've to have this done for you by 5pm on Thursday?

(either with a #define, template, whatever).

#define JonathanFillion Arrogant Asshole

or perhaps:

struct JonathanFillion {};

template<class ArrogantAsshole >
void TempFunc()
{

}

void (&Func)() = TempFunc<Jonath anFillion>;

Don't ask about the particular context -- this is
a totally out of context, _simple_ problem (not that the solution is).

The solution is *extremely* simple. Pity I'm too sadistic to show you how
macros work.

--

Frederick Gotham

Yew, I hope that's not how you talk to your co-workers when they ask
you a question and you don't succeed in giving them a relevant answer.

Chill out, all I was saying is you don't need to paste me your kernel's
source code to answer me; what I'm looking for should be only a couple
of lines.

Don't get heated up for that, for fsck's sake.