I was updating some old code the other day and came across a function which was supposed to delete a pointer passed to it and then set it to null. When the function returned, the pointer was deleted, but was not null. Reason why: the function had been set up wrong:
void deletePointer(XYZ* _xyz)
{
delete _xyz;
_xyz = 0;
}
void callDeletePointer()
{
XYZ* xyz = new XYZ();
...
...
...
deletePointer(xyz);
}
The way deletePointer really needed to be set up is like this:
void deletePointer(XYZ*& _xyz)
{
delete _xyz;
_xyz = 0;
}
Here's why:
The first deletePointer receives a copy of the pointer to _xyz, which allows the user to modify the object addressed by the pointer.
The second deletePointer receives the actual pointer to _xyz, which allows the user to modify the pointer itself.
Oh and one more tip:
When deallocating memory do this:
XYZ* xyz = new XYZ();
delete xyz;
xyz = 0;
instead of:
XYZ* xyz = new XYZ();
if(xyz != 0)
{
delete xyz;
xyz = 0;
}
Apparently, C++ guarantees operator delete() won't be called by a delete if the pointer is 0, so testing for null is not necessary. In fact, if you do include a pointer null test, the test will be done twice.
Source: C++ Primer, Third Edition, by Stanley B. Lippman, Josee Lajoie
More C++
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