Is deleting a pointer same as freeing a pointer (that deallocates the memory)?
Well, no it isn't, since it calls the destructor while free does not!
Francesco
2010-03-15 18:13:54
Furthermore, there's no guarantee that "delete" and "free" work off the same heaps. If you allocate something with "new" and then do a "free" on it, you may corrupt your heap and/or crash your program. Likewise with the "malloc"/"delete" combo.
Will
2010-03-15 18:16:56
Ah my mistake, I was thinking of "free" in a more general, nonkeyword sense
Chris Thompson
2010-03-15 18:19:05
+1
A:
You can't "delete" a pointer variable, only set their value to NULL (or 0).
Alen Sindicic
2010-03-15 18:12:25
+1. This is the correct answer - if Ashish meant a C pointer such as when defining "char *cpString". In C, we never free a pointer, but instead we free allocated memory.
logout
2010-03-15 18:20:07
+6
A:
Deleting a pointer (or deleting what it points to, alternatively) means
delete p;
delete[] p; // for arrays
p was allocated prior to that statement like
p = new type;
It may also refer to using other ways of dynamic memory management, like free
free(p);
which was previously allocated using malloc or calloc
p = malloc(size);
The latter is more often referred to as "freeing", while the former is more often called "deleting". delete is used for classes with a destructor since delete will call the destructor in addition to freeing the memory. free (and malloc, calloc etc) is used for basic types, but in C++ new and delete can be used for them likewise, so there isn't much reason to use malloc in C++, except for compatibility reasons.
Johannes Schaub - litb
2010-03-15 18:14:04
so it all brings back to the difference between in memory management of new/delete and free/malloc ?
CadetNumber1
2010-03-15 18:29:17
a pointer pointing to NULL and a 'deleted' pointer are same or different?
CadetNumber1
2010-03-15 18:30:41
@ashish, yes. malloc and free do only care about the memory, not about the type of what will be in it. `new` cares about the type and calls constructors if necessary, and it can also be extended to get memory from a different memory pool than the default (by writing your own `operator new` and `operator delete` respectively).
Johannes Schaub - litb
2010-03-15 18:32:26
@ashish, changing a pointer's value to null is different from deleting it. The pointer will point to no object afterwards if you only set it to null, but the memory of the object it pointed to previously won't be freed. So in effect you will leak memory by doing that. First delete/free, and then set to null (don't let deleted pointers keep their old value - it will make you unable to test later whether the pointer points to allocated memory or not. That's bad).
Johannes Schaub - litb
2010-03-15 18:34:55
@litb then what will happen if i try to delete a pointer pointing to null?
CadetNumber1
2010-03-15 18:37:08
@ashish, nothing will happen. deleting a null pointer has no effect. See the C++ FAQ for more information about it: http://www.parashift.com/c++-faq-lite/freestore-mgmt.html
Johannes Schaub - litb
2010-03-15 18:38:49
A:
In short, yes.
But you have to be careful: if you allocate with p = new sometype() only then should you use delete p. If you allocate using p = sometype[count] always use delete [] p
And one more thing: you should never pair malloc/delete or new/free.
shinjin
2010-03-15 18:14:20
+2
A:
Yes, delete is used to deallocate memory and call the destructor for the object involved.
It's common pratice to set pointer to NULL after deleting it to avoid having invalid pointers around:
Object *o = new Object();
// use object
delete o; // releases memory and call o->~Object()
o = NULL;
When new and delete are used with standard C types in C++ source they behave like malloc and free.
Jack
2010-03-15 18:15:38
+2
A:
You can't "delete" a pointer variable
Sure you can ;-)
int** p = new int*(new int(42));
delete *p;
delete p; // <--- deletes a pointer
But seriously, delete should really be called delete_what_the_following_pointer_points_to.
FredOverflow
2010-03-15 18:34:13