The use of ReAlloc function __ function

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
using namespace Std;
void Setval (char *tmp,int qs,int num,char mm)
{
for (int i=qs;i<num-1;i++)
{
* (tmp+i) =mm;
}
* (tmp+num-1) = ' ";
}
int main ()
{
Char *p,*q;

Shorten memory
p = (char *) malloc (1000);
Setval (p,0,1000, ' a ');
Q = (char *) realloc (p,800);
if (q!=null)
{
Setval (q,795,800, ' S ');
cout<<q<<endl;
cout<< "Success" <<endl;
}
Else
{
Setval (p,500,800, ' F ');
cout<< "Fail" <<endl;
}
Free (q);
GetChar ();
GetChar ();
System ("pause");
return 0;
}

ReAlloc can enlarge or shrink the space indicated by the given pointer, and the contents of the original memory will remain unchanged. Of course, for shrinking, the content of the part that is shrunk is lost.

ReAlloc does not guarantee that the adjusted memory space retains the same memory address as the original memory space. Conversely, the pointer returned by ReAlloc is likely to point to a new address:

Because ReAlloc allocates memory from the heap, when a chunk of memory is enlarged, the realloc gets the additional bytes directly from those bytes behind the existing data on the heap, but if the byte behind the data is not enough, then the first free block with enough size on the heap is used. The existing data is then copied to the new location, and the old block is put back on the heap.
In the code, if we use the int* memory mode of i = (realloc) (I, 2*sizeof (int)), there are two scenarios:

1. Assign success, return void* pointer: realloc return value if the value is different from the previous malloc, then the ReAlloc function is complete, I point to the old memory automatically free.
2. Allocation failure, return null value: At this time, I originally pointed to the memory has not been free, and now can not find the address, this appears memory leak.

Workaround: Define another pointer J to receive the ReAlloc return value, determine if it succeeds, and succeed to assign J to I

Article from: http://blog.csdn.net/leopardaa521/archive/2009/10/12/4658887.aspx