Why a variable length array compiles in this c++ program?

Question

It is said that arrays are allocated at compile time, then the size must be const and available at compile time.
But the following example also works, Why?

#include <iostream>                                  
#include <vector>                                                 
using namespace::std;                                             
int main()                                                       
{                                                    
    vector<int> ivec;                                               
    int k;                                                  
    while(cin>>k)                                              
        ivec.push_back(k);                                     
    int iarr[ivec.size()];                                           
    for (size_t k=0;k<ivec.size();k++)                                 
    {                                                             
        iarr[k]=ivec[k];                                               
        cout<<iarr[k]<<endl;                                   
    }                                                            
    return 0;                                                    
}   

Answer 1

Compile your code with -pedantic.
Most compilers support variable length arrays through compiler extensions.
The code works due to the compiler extensions, However as you noted the code is non standard conforming and hence non portable.