delete[] or delete?

[X PaYnE X]

We had a computers lesson yesterday and our teacher was explaining pointers and how to allocate memory.. etc.. using new and delete([]).

At one point, she said:

char* strng = new char[astring.getCount() + 1];

for (i = 0; i < astring.getCount(); i++)
{
	strng[i] = astring.getCharacter(i);
}

strng[i] = '\0';

//do something with strng

delete strng;

I always thought it was delete[] strng, since strng is allocated as an array? I didnt want to correct the teacher since well, i didnt want to be wrong, but im almost 100% sure that its delete[] and not delete...

[joshdick]

If you use new, use delete. If you use new[], use delete[].

You are right. Your teacher goofed. Most teachers I know appreciate being corrected, as do I as a teaching assistant.

[7smurfs]

What happened to teaching the STL?

Anyways...both compile(for me) but I don't know if it actually works both ways.

[X PaYnE X]

ah, thanks for the quick reply, i was beginning to doubt my own knowledge...

its really annoying when a teacher says something wrong and its like you have to force yourself to beleive him/her because he/she is a teacher...

anyway, thanks again.

edit: the teacher wants to leave STL to the end, she thinks if we can make do without STL then we'd do even better with it.

[Fordy]

delete [] has the advantage of calling destructors on all objects of the array, if you use the standard delete, you risk the chance of memory leaks or worse.

For chars and ints etc, it probably wont make a difference, but the standard says that you must match both forms of delete and new, so not doing so could result in undefined behavior

[Micko]

delete [] has the advantage of calling destructors on all objects of the array, if you use the standard delete, you risk the chance of memory leaks or worse.

Yes, Fordy is right, to help you understand problem try this code

#include <iostream>
#include <cstdlib>

using namespace std;


class MyClass
{
      int x;
      public:
             MyClass()
             {
                      cout<<"Constructor!"<<endl;
             }
             ~MyClass()
             {
                       cout<<"Destructor!"<<endl;
             }
};

int main()
{
    MyClass *pobj = new MyClass[5];
    
    delete [] pobj;
   //delete pobj;
    
    system("pause");
}

After trying, comment line with [] and uncomment line with delete pobj. Observe what happens.
What would happen if in MyClass was int *x , constructor allocated memory and destructor deallocated memory?

After that, post your conclusion here!

[Joelito]

Ah so... If I understood:
I should use delete[] whe the allocation was from new[] and delete from new?

// ...
int main()
{
// ...
MyClass *mc = new MyClass;
//...
delete mc;
//...
char* s = new s[256];
//...
delete s[]:
//...
return 0;
}

[joshdick]

Precisely! That's all there is to it, Joelito.