How is it possible this array compiles?

[JiiPee]

How is it possible this array compiles? Last time I studied C++ the
array size must be a constant value (double checked: "NOTE: The
|elements| field within square brackets |[]|, representing the number of
elements in the array, must be a /constant expression/"). How is it
possible howMany can be a variable below? Obviously there is something I
do not see... But I do see a normal array int arr[howMany]; .... so...

#include <iostream>

using namespace std;

int main()
{
int howMany;
cout << "How big array?: ";
cin >> howMany;

int arr[howMany];
if(howMany > 5)
{
arr[howMany-2] = 67;
cout<<arr[howMany-2];
}

return 0;
}

[Martijn Lievaart]

martijn@garfield:~/t$ g++ -std=c++11 -pedantic -c -o vararray.o
vararray.cpp
vararray.cpp: In function ‘int main()’:
vararray.cpp:11:21: warning: ISO C++ forbids variable length array
‘arr’ [-Wvla]
int arr[howMany];
^

It's an extension from C, known as Variable Length Array (VLA). It's not
legal C++. It's accepted by many compilers unless you tell them to be
pedantic.

HTH,
M4

[JiiPee]

oh ok, thanks. So I guess its not totally portable neither as its not
legal.... so not good to use I would think.