Thread: Lot of questions.

Originally Posted by laserlight

It is a major mistake. By assigning the address of x to p, p now points to an object that will be automatically destroyed. As such, delete p; becomes a mistake. Furthermore, the object that was created on the previous line cannot be destroyed because there is no way to access it.

In the code though the first one needs to be there right? where it says:

Code:

p = &i;

Does that need to be there or would thta delete the i later?

Originally Posted by laserlight

Yes. The i variable would be automatically destroyed when at the end of the function. This has nothing to do with pointers but with the lifetime of such variables.

When would the i variable be destroyed. would it be destroyed when p was assigned to a new variable?

i was just wondering how to add body to a code, like how could i add body to a switch case like this:

Code:

   int input;
    int* p;             //not sure if the pointer would en up looping it but i just added this to give
    p = &input;     //it a try if the program would run.
    
    cout<<"1. Play Game\n";
    cout<<"2. Load Game\n";
    cout<<"3. Play Multiplayer\n";
    cout<<"4. Exit\n";
    cout<<"Selection: ";
    cin>> input;
    switch ( input ) {
           case 1:
                playgame();
                break;
           case 2:
                loadgame();
                break;
           case 3:
                playmultiplayer();
                break;
           case 4:
                cout<<"Thank you for playing!\n";
                break;
           default:
                   cout<<"Error, bad input.\n";
                   cout<< *p <<"\n";
                   break;

The program compiles but it doesn't run ( this is the script from the tut, by the way). The tutorials said that it wouldn't run because the functions dont have bodies. It's told me to add 'if' functions (i think thats what it was asking, that or it was comparing) I was just wondering how to give the functions bodies. I tried just simply adding a cout<< but that din't work. What would i need to do to make the program run?

i is a local variable which would fall out of scope when the function returns, the pointer has nothing to do with it.

p = new int(x);
p = &x;
// ...
delete p;

That might not match the code you gave us but it doesn't matter, the problem is the same. The error here is two-fold:

a) the memory returned by new is an inaccessible object, thanks to the subsequent reassignment. This is called a memory leak, because you won't get that memory back until the program terminates.

b) delete is a mistake. p points to the x variable, which would fall out of scope on it's own.

When pointers point to something returned by new or new [] you should clean up those objects with a matching delete/delete [] before reassigning the pointer or before the pointer variable falls out of scope.

Originally Posted by whiteflags

When pointers point to something returned by new or new [] you should clean up those objects with a matching delete/delete [] before reassigning the pointer or before the pointer variable falls out of scope.

The added delete doesn't really seem to have any effect with the outcome but i guesse it's better safe then sorry. Thanks for the tip. So something like this?

Code:

int i(25 + 4);
    int x(4);
    int *p;
    p = &i;
    cout<< *p <<"\n";
    cout<< *p <<"\n";
    delete p;
    p = new int(x);
    p = &x;
    cout<< *p <<"\n";
    delete p;
    p = 0;
    cin.get();

ao my previous code was alot better... Then what needs to be fixed???!!!

(Previouse code)

Code:

#include <iostream>

using namespace std;

int main()
{
    int i(25 + 4);
    int x(4);
    int *p;
    p = &i;
    cout<< *p <<"\n";
    cout<< *p <<"\n";
    p = new int(x);
    p = &x;
    cout<< *p <<"\n";
    delete p;
    p = 0;
    cin.get();
}

Why is this hard?

Code:

int i = 29;
int x = 4;
int *p;

p = &i;

cout << *p << "\n";

p = new int(x);

cout << *p << "\n";

delete p; //done with p

cin.get();

Originally Posted by whiteflags

Why is this hard?

Code:

int i = 29;
int x = 4;
int *p;

p = &i;

cout << *p << "\n";

p = new int(x);

cout << *p << "\n";

delete p; //done with p

cin.get();

THATS EXACLTY WHAT I WROTE BEFORE!!!!!! (well not when i showed the "previouse code", i made a mistake, i forgot to take out the p = &x) I wrote that in my code then you sayd that i wrote it wrongand that i needed to add a delete somwhere. I added the extra cout<< as a little test, I just wanted to see that the pointer was working. I put the delete in the wrong place so someone else told me not to put a delete where i had placed it and that it was dangerous to delete something that wasn't assigned with new. It's not hard its just i have no friggin clue as to what you guys are trying to say!!!

You told me that the delete was a mistake, but then you showed me this code which is exactly what i did before that you said was wrong!

Originally Posted by whiteflags

Why is this hard?

he's a noob... try to cut him a bit of slack. the idea was to GUIDE him in the right direction so that he would come up with the code that you wrote on his own. Now you just handed it to him and he learns nothing.

Originally Posted by Elkvis

he's a noob... try to cut him a bit of slack. the idea was to GUIDE him in the right direction so that he would come up with the code that you wrote on his own. Now you just handed it to him and he learns nothing.

I dont need any slack, he wrote the exact same code that i had before! he told me that i needed to do something to delete, but the delete that i had was in the right place so i thought he meant something else. So i added that extra delete which was wrong because the int that i used it with was not associated with new. then he writes the exact same code that i had written before but without one of the cout<< functions. Technically he didn't hand me anything because i was right the whole time!

If you had read the other threads you would have noticed that laserlight had corrected me on the p = &x. I added the p = 0 because the tutorials said that making it a null pointer was a good idea. When i reposted the final code i had forgotten to take out the p = &x which i pointed out in my response to whiteflag I'm sorry, is almost completely my fault. I agree that i am a noob and that i sometimes have no idea what the heck im, or what anyone else is talking about. For example, what do you mean by "lose hold of" the pointer?