When are variable-length arrays legal?

Question

I\'m not a C++ expert, but as far as I know this code should fail due to size not being constant:

#include

using namespace std;         


        

Answer 1

c99 supports variable length arrays(VLA) but neither c90 nor C++ supports variable length arrays, but gcc support this as an extension in both C and C++ you can see this more clearly if you compile with these arguments:

gcc -std=c89 -pedantic

this will give you the following warning:

warning: ISO C90 forbids variable length array ‘array’ [-Wvla]

or with g++:

g++ -pedantic

will give you this warning:

warning: ISO C++ forbids variable length array ‘array’ [-Wvla]

this standards section in the gcc manual goes into more details. Important to note that as of the 2011 C standard variable length arrays(VLA) are now optional.