working of range for loop and C-style arrays in C++ [duplicate]

C-style Arrays are not self-describing as it doesn't has any information about it's size, so for iterating it's elements we need size information somehow. I'm confused as how range-for loop gets the size information. It is expected to fail. Consider 2 conflicting examples,

#include <iostream>
using namespace std;

int main() { 
    int a[] = { 1, 2, 3, 4, 5, 6 };
    for(auto x : a)
        cout<<x<<" ";
    cout<<endl;
    return 0;
}

It ran successfully(unexpected), but

#include <iostream>
using namespace std;

void print_a(int*);

void print_a(int a[])
{
    for(auto x : a)
        cout<<x<<" ";
    cout<<endl;
}
int main() { 
    int a[] = { 1, 2, 3, 4, 5, 6 };
    print_a(a);
    return 0;
}

This produced errors(expected).

Can someone explain as how range-for loop actually works ?