C++ Initializing an array with a variable and not a constant expression -

i in process of learning c++ , have been reading c++ primer (5th edition).

in chapter 3.5 talks arrays , initializing them, says arrays must initialized using constant expression.

here example book

unsigned cnt = 42; // not constant expression constexpr unsigned sz = 42; // constant expression int arr[10]; // array of ten ints int *parr[sz]; // array of 42 pointers int string bad[cnt]; // error: cnt not constant expression string strs[get_size()]; // ok if get_size constexpr, error otherwise”  excerpt from: stanley b. lippman. “c++ primer, fifth edition.”  

however when try using g++ -std=c++11 compiles fine. kind of confused whether mistake in book or has standard been modified since writing of book though book states uses c++ 11.

here actual code using compiles , runs fine

unsigned int cnt = 42; // not constant expression constexpr unsigned int sz = 42; // constant expression  int arr[10]; // array of 10 ints int *parr[sz]; // array of 10 int pointers string bad[cnt]; 

i tried this

int var = 2; int size = var; int int_arr[size]; 

and works.

if has explanation or why works though states shouldn't appreciate it.

thanks!

variable length arrays extensions built compiler c++11 , not standard, if compile -wvla flag see compiler emit error code.

you better of using std::vector dynamic arrays instead. if not familiar how use suggest looking around online. there plenty of sources go detail how use std::vector , how works.