Re: Getting memory size

Nimish wrote:

> Hi all
> 
> How can I find the size of memory allocated to the pointer.
> For eg.
> 
> int main()
> {
>              int b[100];
>              int *a = b;
>              ....
>              ....
>              return 0;
> }
> 
> In this function I want to get size of memory allocated to "a"
> pointer.
> How can this be done.
> 

A pointer includes no accessible information about the total size of
the memory block it points at (or the number of elements in an array).


You need to explicitly track that yourself.

For example,

    size_t  elements_of_a = 100;
    size_t  memory_usage_of_a = elements_of_a*sizeof(int);

A technique can be used for arrays is

int main()
{
      int b[100];
      size_t elements_of_b = sizeof(b)/sizeof(b[0]);
           // will yield 100
}

but that does not work for pointers.

int main()
{
      int b[100];
      int *a = b;
      size_t elements_of_a = sizeof(a)/sizeof(a[0]);
          //  will yield sizeof(int *)/sizeof(int)
}

For example, on a 32 bit computer with 8-bit bytes and an int
that is 4 bytes sizeof(int *) will [often] be 4 and sizeof(int)
will also be 4, so elements_of_a will be 1.   The value may be
different on other machines, but will not be related to the
number of elements in b.

If you employ standard containers (std::vector, etc) the container
does keep track of the number of elements it contains.

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