Is there a way to define array size based on command line argument? Run time vs compile time instantiation?

I have a global array of size DIMENSIONS: DIMENSIONS is a static global variable. I can change the hardcoded DIMENSIONS variable without issues in compilation or execution, but is there a way to determine this value at compile time versus run time?

const static unsigned int DIMENSIONS = 2;
std::array<double, DIMENSIONS> arr;

// ...
// ...
// ...

int main (int argc, char* argv[]) {
    // argv[0] contains value '4'
}

If I made DIMENSIONS non-constant non-static, is there a way to reinitialize it as argv[0] in main() and have arr still instantiate properly?

I'd like to control the dimensionality of my program (it's meant for hill climbing optimization) through the command line. I understand arrays cannot have dynamic sizing and besides VLAs, must have their size declared at compile time, not run time. I specifically need a global non-VLA, though.