Array size at run time without dynamic allocation is allowed?

Question

I\'ve been using C++ for a few years, and today I saw some code, but how can this be perfectly legal?

int main(int argc, char **argv)
{
    size_t size;
             


        

Answer 1

I recently came across a scenario where a stack-allocated array is desired. (It's a wrapper around v8, needed an array of args on every method call).

An std::vector would do heap memory allocation, whose performance is not acceptable.

Here is my solution, use template to allocation array of cases:

template
static void call(...) {
    v8::Local v8Args[Argc];

    // use v8Args
    ...
}

template
static void callV8Function(size_t argc, It argvBegin, It argvEnd,) {
    // C++ don't have dynamic stack allocation (like C99 does)
    // try to avoid heap-allocation...
    if (argc <= 4) {
        return callV8FunctionOnStack<4>(...);
    } else if (argc <= 8) {
        return callV8FunctionOnStack<8>(...);
    } else if (argc <= 16) {
        return callV8FunctionOnStack<16>(...);
    } else if (argc <= 32) {
        return callV8FunctionOnStack< 32>(...);
    } else {
        std::vector> v8Args(argc);
        // fallback to vector
   }
}

(And of course, I can just do with a 32-sized array, but which is not so elegant.)