Automatic variable

Hello everyone,


I have searched and found the term automatic variable means function local variable, compared with static and global variable. Is that correct?


thanks in advance,
George

Yes, that's what it means.

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Mats

It means a variable that will be destroyed as soon as it goes out of scope (i.e. not a pointer, since you manually have to free() them)

I think I've also seen an auto keyword, although I don't see why you would ever need to use it since it's auto by default?

Yes, auto is a keyword in C. It doesn't provide much usefullness tho'. In Bjarne's book, it says "If you absolutely must be explicit about this, C++ provides the redundant keyword auto" [This is the ONLY reference to auto anywhere in the book].

--
Mats

Quote:

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Originally Posted by cpjust

It means a variable that will be destroyed as soon as it goes out of scope (i.e. not a pointer, since you manually have to free() them)

I think I've also seen an auto keyword, although I don't see why you would ever need to use it since it's auto by default?

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I, for one, am glad for the presence of the auto keyword. There are rumblings afoot that this keyword will be co-opted to a new use in the new C++ standard. It will mean "whatever type makes this declaration valid." Should prove extremely useful for metaprogramming.

Example

Code:

---

auto x = boost::some_crazy_object();

---

Where the type of boost::some_crazy_object() might be some enormous 5000-character long template typename, which you neither care to infer nor could even if you wanted to. "auto" in this case means "that type," so you can easily declare x without having to figure out what exact type is being used.

Also, I hope they allow it for return types from template functions (allowing it for normal functions would be unreasonable and probably impossible to implement):

Code:

---

template <typename T>
auto my_func(T blah)
{
    return some_crazy_thing(blah);
}

---

Where the return type is whatever type some_crazy_thing(blah) is.

Can't wait!

Quote:

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Originally Posted by brewbuck

I, for one, am glad for the presence of the auto keyword. There are rumblings afoot that this keyword will be co-opted to a new use in the new C++ standard. It will mean "whatever type makes this declaration valid." Should prove extremely useful for metaprogramming.

Example

Code:

---

auto x = boost::some_crazy_object();

---

Where the type of boost::some_crazy_object() might be some enormous 5000-character long template typename, which you neither care to infer nor could even if you wanted to. "auto" in this case means "that type," so you can easily declare x without having to figure out what exact type is being used.

Also, I hope they allow it for return types from template functions (allowing it for normal functions would be unreasonable and probably impossible to implement):

Code:

---

template <typename T>
auto my_func(T blah)
{
    return some_crazy_thing(blah);
}

---

Where the return type is whatever type some_crazy_thing(blah) is.

Can't wait!

---

I highly doubt they would change the meaning of auto since it would completely break backwards compatibility with C & current C++.

Quote:

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Originally Posted by cpjust

I highly doubt they would change the meaning of auto since it would completely break backwards compatibility with C & current C++.

---

It's being seriously discussed. Might not happen but I don't "highly doubt" it.

It would break backwards compatibility with existing C and C++ programs that actually use the auto keyword. I don't know if this is better than introducing a new keyword or not, because a new keyword could have been used for a variable name in existing code.

Or the new keyword could be named something like _Bool. :) But that is hard to type and so they introduced a new header for bool, an easier name to swallow.

>> There are rumblings afoot that this keyword will be co-opted to a new use in the new C++ standard.

off-topic, but in addition to this I believe a typeof keyword is being considered as well, eg:

Code:

---

typedef typeof(insane_template_instantiation) type;

---

or was I just daydreaming? :D

Apparently not. http://www.boost.org/doc/html/typeof.html