How to get the length of an array from a pointer? [duplicate]

Answer 1

It is true that you cannot get the array size from a pointer to an element of the array.

If the reason you only have a pointer is because you are implementing a function that takes an array parameter as an argument like this:

void foo (T *p) {
    // p is a pointer to T
}

then you can use a template function instead to get the array size to the function.

template 
void foo (T (&p)[N]) {
    // p is a reference to an array[N] of T
    std::cout << "array has " << N << " elements" << std::endl;
    std::cout << "array has "
              << sizeof(p)/sizeof(p[0])
              << " elements"
              << std::endl;
}

int main ()
{
    int array[40];
    char array2[25];
    foo(array);
    foo(array2);
    return 0;
}