Why is this considered an extended initializer list?

Question

#include <vector>

struct foo {
    int i;
    int j;
    int k;
};

int main() {
    std::vector<foo> v(1);
    v[0] = {0, 0, 0};
    return 0;
}

When compiling this using g++, I get the following warning:

warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x [enabled by default]

As far as I can tell, though, it's just a normal initializer list. The struct is a POD type.

Is this a bug or am I missing something?

Answer 1

Pre C++11 (and possibly C99) you can only initialize a POD at creation, not at arbitrary runtime points, which is what you're attempting here (assignment from an initializer list).

You can make a null_foo though:

int main()
{
    const foo null_foo = {0, 0, 0};
    std::vector<foo> v(1);
    v[0] = null_foo;
    return 0;
}

Answer 2

Brace-initialization for aggregates is only valid during declaration-initialization:

Foo a = { 1, 2, 3 };

It is not a way to generate temporaries midway: some_function(true, {1,2,3}, 'c').

C++11 adds uniform initialization in which you can indeed write f(Foo{1,2,3});.