memory usage question

[Sean P.]

why does "int *iptr = new int[1024];" use up to 8KB of memory when i
only declared a ptr to 1024 integers? Intuitively, it should be only
1024*sizeof(int)+4 (for the pointer). Does C++ add an accompanying
pointer to every element or something? thanks.

 

[John Dibling]

why does "int *iptr = new int[1024];" use up to 8KB of memory when i
only declared a ptr to 1024 integers? Intuitively, it should be only
1024*sizeof(int)+4 (for the pointer). Does C++ add an accompanying
pointer to every element or something? thanks.

How did you determine the memory usage?

</dib>

John Dibling
email: dib@substitute_my_full_last_name_here.com
Witty banter omitted for your protection

 

[David White]

why does "int *iptr = new int[1024];" use up to 8KB of memory when i
only declared a ptr to 1024 integers? Intuitively, it should be only
1024*sizeof(int)+4 (for the pointer). Does C++ add an accompanying
pointer to every element or something? thanks.

How do you know that 8 kb has been used? What is sizeof(int) on your
machine?

Pedantic note: "Usage" means _how_ something is used, not how much.

DW

 

[John Harrison]

why does "int *iptr = new int[1024];" use up to 8KB of memory when i
only declared a ptr to 1024 integers? Intuitively, it should be only
1024*sizeof(int)+4 (for the pointer). Does C++ add an accompanying
pointer to every element or something? thanks.

There is always a small overhead when allocating memory. But there is no way
that on a system where sizeof(int) == 4 that allocating 1024 ints uses 8Kb.
More likely your method of finding out how much memory is being used is
faulty.

john

 

[Harald Grossauer]

why does "int *iptr = new int[1024];" use up to 8KB of memory when i
only declared a ptr to 1024 integers? Intuitively, it should be only
1024*sizeof(int)+4 (for the pointer). Does C++ add an accompanying
pointer to every element or something? thanks.

Maybe your machine has a page size of 4kb, then
4*sizeof(int)+a_little_bit_overhead takes two pages.