Looking at the C++ new[] cookie. How portable is this code?
- by carleeto
I came up with this as a quick solution to a debugging problem - I have the pointer variable and its type, I know it points to an array of objects allocated on the heap, but I don't know how many. So I wrote this function to look at the cookie that stores the number of bytes when memory is allocated on the heap.
template< typename T >
int num_allocated_items( T *p )
{
return *((int*)p-4)/sizeof(T);
}
//test
#include <iostream>
int main( int argc, char *argv[] )
{
using std::cout; using std::endl;
typedef long double testtype;
testtype *p = new testtype[ 45 ];
//prints 45
std::cout<<"num allocated = "<<num_allocated_items<testtype>(p)<<std::endl;
delete[] p;
return 0;
}
I'd like to know just how portable this code is.
