How do I find the length of an array?

c++ arrays
Maxpm picture Maxpm · Nov 5, 2010 · Viewed 1.5M times · Source

Is there a way to find how many values an array has? Detecting whether or not I've reached the end of an array would also work.

Answer

Oliver Charlesworth picture Oliver Charlesworth · Nov 5, 2010

If you mean a C-style array, then you can do something like:

int a[7];
std::cout << "Length of array = " << (sizeof(a)/sizeof(*a)) << std::endl;

This doesn't work on pointers (i.e. it won't work for either of the following):

int *p = new int[7];
std::cout << "Length of array = " << (sizeof(p)/sizeof(*p)) << std::endl;

or:

void func(int *p)
{
    std::cout << "Length of array = " << (sizeof(p)/sizeof(*p)) << std::endl;
}

int a[7];
func(a);

In C++, if you want this kind of behavior, then you should be using a container class; probably std::vector.

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