How to calculate size of array from pointer variable?

1. If you have only a pointer, the answer is no.

std::size_t getsize(int* parray) {
   return 0; // sorry, no way to tell!
}

2. If you have s statically allocated array, you can determine the number of elements from the arrays name. However, if that is the case, and you don't use C++ functionality, then most likely there wouldn't be a need for this in the first place.

int array[10];
std::size_t length = 10; // big surprise, that number is right in the definition!

or:

int array[] = {4,78,3,7,9,2,56,2,76,23,6,2,1,645};
std::size_t length = sizeof(array)/sizeof(int); // see solution 1

3. Alternately, use the containers from the STL, e. g. std::array or std::vector. These containers behave very similar to standard arrays, but you can query their size at runtime, no problem.

std::vector<int> array;
array.pushback(2);
array.pushback(7);
array.pushback(344);
array.pushback(45);
array.pushback(89);
array.pushback(28);
std::size_t length = array.size(); // easy!

If you have ONLY the pointer that is passed to the procedure, you can't do OriginalGriff's solution[^]. You will need to explicitly pass the size of the array to the function. This is not uncommon in C/C++ development. Lot of C library functions have this behavior.

Repost!

See here: Same question posted @ StackOverflow[^]

Hi,

<pre>sizeof(arrayname);</pre>

will do the trick..

Thanks,

Please see my article here:How to get size of array from its pointer[^]