Why can I define this variable length array in C++? [duplicate]

Question

Given

gcc -c main.C
gcc -lstdc++ -o main main.o

And main.C being

#include <iostream>

int main() { 
    int somany; 
    std::cin >> somany; 
    double ex[somany]; 

    for(int i=0;i<somany;i++){ 
            ex[i]=0.03; 
            std::cout << ex[i]; 
    } 
}

Why does this not result in a compiler error? I thought C++ does not have VLAs?

Executing the program works just fine.

It's a gcc extension. You're right that it's not in the standard. — jrok
– jrok, Commented Sep 16, 2014 at 12:41
How can I compile against the c++ standard only? Is there some flag for gcc? (g++ is not available for me atm) — ben
– ben, Commented Sep 16, 2014 at 12:42
If anybody knows how to make the title of the question more specific feel free to edit. — ben
– ben, Commented Sep 16, 2014 at 12:44

Lightness Races in Orbit · Accepted Answer · 2014-09-16 12:55:24Z

0

This is a GCC extension and doesn't have anything to do with your approach of compiling with gcc then manually linking the C++ standard library.

The --pedantic compilation flag will typically disable such extensions.

answered Sep 16, 2014 at 12:55

Lightness Races in Orbit

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