clearing memory allocated to a struct

I'm having trouble figuring out how to free memory allocated to a
struct. Here's my code:

Code:

//global defines
struct Test
{
   long l;
   int i;
   char c[20];
   bool b;
};

Test tTest;

//initialization
tTest.l=1233455;
tTest.i=12;
strcpy(tTest.c,"TestChar");
tTest.b=true;

//test/deallocation (this is what I can't get right)
if(&tTest)
{
    MessageBox(NULL,"Allocated","Debug",NULL);
    tTest.l=NULL;
    tTest.i=NULL;
    strcpy(tTest.c,"");
    tTest.b=NULL;
}
else
{
   MessageBox(NULL,"Memory cleared","Debug",NULL);
}

I've also tried:

Code:

Test* tTest;

//initialization
tTest=new Test[1];
tTest->l=1233455;
tTest->i=12;
strcpy(tTest->c,"TestChar");
tTest->b=true;

//test/deallocation (this is what I can't get right)
if(tTest)
{
    MessageBox(NULL,"Allocated","Debug",NULL);
    delete [] tTest;
}
else
{
   MessageBox(NULL,"Memory cleared","Debug",NULL);
}

With the second bit of code I get the following error:

Debug Assertion Failed!

Anybody know what I'm doing wrong?

AAAGGGHHH!

Ok, now I've got it to work (that is return the message I want)
but I'm not sure if it's doing what I really want in the background.

what I did was using the second code snippet I replaced the
line:

Code:

delete [] tTest;

with this:

Code:

tTest=NULL;

By setting the pointer to the structure to NULL am I really freeing
the memory? (I'm sorry if this is a stupid question, but I've never
really learned that much about memory management and I'm
trying to learn it now; playing catch up I guess)

I shook the 8 ball and it said you had to release it back to the heap. NULL still occupies the address. Que no? Of course, the 8 ball (or Horton) could be wrong.

The delete (or delete[] for arrays) will free the memory up to be used again. Setting the pointer to NULL is a safety measure because technically it still "points" to the memory location (dangling pointer). You could in theory still use the pointer but the memory may have been reallocated. You set the pointer to NULL to prevent accidental use after the memory has been released. If you set the pointer to NULL before releasing it you end up with a memory leak which is where you've allocated memory but have no way to access it anymore.