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ShurikeN
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 Posted: Sat Jan 10, 2009 5:49 am Post subject: [Question] new/delete operators |
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I read a book that says when you use new, you clean up with delete. When you use new[] (with brackets), you clean up with delete[] (with brackets).
but what if:
| Code: |
int main()
{
player = new Player;
player = new Player;
player = new Player;
}
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since they are not array i cannot use delete[], how do i actually delete them properly?
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Jani
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| Posted: Sat Jan 10, 2009 5:56 am Post subject: |
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| Code: |
Player p1 = new Player;
Player p2 = new Player;
Player p3 = new Player;
delete p1;
delete p2;
delete p3;
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| Code: | Player p[3];
for(int i=0; i<3; ++i)
p[i] = new Player;
for(int i=0; i<3; ++i)
delete p[i] |
| Code: | Player *p = new Player[3];
delete [] p; |
EDIT: Missed a [/code].
EDIT2: Moar examples.
Last edited by Jani on Sun Jan 11, 2009 6:27 am; edited 3 times in total |
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Zerith
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| Posted: Sat Jan 10, 2009 7:40 am Post subject: |
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Jani, i think he meant something else.
ShurikeN: You should never do a thing like that, it would be impossible to delete those since you are assigning a new portion of memory every time and lose track of the older one.
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&Vage
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| Posted: Sat Jan 10, 2009 4:20 pm Post subject: |
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| Isn't delete for non array variables and delete[] for arrays?
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Noz3001
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| Posted: Sun Jan 11, 2009 5:48 am Post subject: |
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| You should have 2 pieces of memory allocated which you cant remove.
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Jani
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| Posted: Sun Jan 11, 2009 6:39 am Post subject: |
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Actually.. If you wanted to do it like that, you could build your own garbage collector in the class, similar to Java's one. I mean it'd delete itself it there's no more references to that object.
Let's say something like this: | Code: | class Player
{
private:
static void* m_p;
public:
Player();
};
void* Player::m_p=0;
Player::Player()
{
if( m_p )
delete m_p;
m_p = this;
}
int main(int argc, char *argv[])
{
Player *p;
p = new Player();
p = new Player();
p = new Player();
delete p;
return 0;
} |
Iono if it works, but you got the idea. Too lazy to test :p
EDIT: if you wanted to keep all the references and just delete them later: | Code: | #include <vector>
#include <iostream>
class Player
{
private:
static std::vector<void*> *m_v;
public:
Player() { m_v->push_back(this); }
~Player() {
for(unsigned int i=m_v->size()-1; i>0; --i)
delete m_v->at(i);
delete m_v;
}
unsigned int Count() { return this->m_v->size(); }
};
std::vector<void*> *Player::m_v = new std::vector<void*>();
int main(int argc, char *argv[])
{
Player *p;
p = new Player();
std::cout << p->Count() << std::endl;
new Player();
std::cout << p->Count() << std::endl;
new Player();
std::cout << p->Count() << std::endl;
delete p;
return 0;
} |
Last edited by Jani on Sun Jan 11, 2009 7:00 am; edited 1 time in total |
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ShurikeN
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| Posted: Sun Jan 11, 2009 6:45 am Post subject: |
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Zerith, thank you, you got my point. Actually i was creating a program for about a week and when i have completed it i did some clean up and i noticed a portion of my code that does exactly what i illustrated above. It wasn't producing any error but i had a feeling that it was WRONG. so thank you for clearing that up.
Thanks also Jani, i appreciate your help.
Edit:
Wow, thanks for your code sample jani. i'll try that.
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Jani
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| Posted: Sun Jan 11, 2009 7:03 am Post subject: |
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| ShurikeN wrote: | Edit:
Wow, thanks for your code sample jani. i'll try that. |
Hehe, np. You might want to create some at(int index) function if you want to access specific Player.
Also, it'd be way more reasonable to create a vector and allocate players there than creating a vector wrapper like this :P
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ShurikeN
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| Posted: Mon Jan 12, 2009 11:20 pm Post subject: |
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like this?
| Code: |
std::vector<Player*> players;
Player *player;
player = new Player();
players.push_back( player );
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Skyance
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| Posted: Tue Jan 13, 2009 3:51 am Post subject: |
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Yes, but you can simply do:
| Code: | | players.push_back(new Player()); |
Then you don't need another temporaty pointer to the new Player object.
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Jani
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| Posted: Tue Jan 13, 2009 1:29 pm Post subject: |
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| ShurikeN wrote: | | like this? |
Yup, or just directly push the allocated object: | Code: | std::vector<Player*> players;
players.push_back( new Player() ); |
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&Vage
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| Posted: Tue Jan 13, 2009 4:02 pm Post subject: |
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| You need to resize the vectors everytime you push_back.
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smartz993
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| Posted: Tue Jan 13, 2009 4:12 pm Post subject: |
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| _void_ wrote: | | You need to resize the vectors everytime you push_back. |
You are scary dumb. Stop trying to help people, you can't.
push_back will resize the vector if it does not have the necessary capacity.
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&Vage
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| Posted: Tue Jan 13, 2009 7:21 pm Post subject: |
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| smartz993 wrote: | | _void_ wrote: | | You need to resize the vectors everytime you push_back. |
You are scary dumb. Stop trying to help people, you can't.
push_back will resize the vector if it does not have the necessary capacity. |
I tried it already pussy I always have a capacity error.
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smartz993
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| Posted: Tue Jan 13, 2009 7:42 pm Post subject: |
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| Code: | | void push_back ( const T& x ); |
| cplusplus.org wrote: | Add element at the end
Adds a new element at the end of the vector, after its current last element. The content of this new element is initialized to a copy of x.
This effectively increases the vector size by one, which causes a reallocation of the internal allocated storage if the vector size was equal to the vector capacity before the call. Reallocations invalidate all previously obtained iterators, references and pointers. |
Size != Capacity.
Size is how many elements are in your vector.
The resize function will only increase capacity if you want to resize to larger than the current capacity.
The reserve function will make the capacity to at least(sometimes more) the number in the parameter you give it.
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