c++ - g++ variable size array no warning?

Question

int a;
cin >> a;
int ints[a];

Why does this not throw any kind of warning while compiling? How do I know when this array thing is actually using the heap or the stack?

g++ -std=c++11 -Wall *.cpp -o main

Answer 1

ISO C++ disallows the use of variable length arrays, which g++ happily tells you if you increase the strictness of it by passing it the -pedantic flag.

Using -pedantic will issue a warning about things breaking the standard. If you want g++ to issue an error and with this refuse compilation because of such things; use -pedantic-errors.

---

g++ -Wall -pedantic -std=c++11 apa.cpp

apa.cpp: In function ‘int main(int, char**)’:
apa.cpp:8:13: warning: ISO C++ forbids variable length array ‘ints’ [-Wvla]
   int ints[a];
             ^
apa.cpp:8:7: warning: unused variable ‘ints’ [-Wunused-variable]
   int ints[a];
       ^