C++0x Initializer Lists

Question

I need some help understanding some subtleties of C++0x consolidated initializer lists.

Why does...

#include <iostream>

int main()
{
    struct Foo
    {
        public:
            struct Bar
            {
                public:
                    Bar(int a, int b, int c){}

                    int ma, mb, mc;
            } mBar[2];

            Foo(int a, int b, int c)
            : mBar{{a, b, c},
                   {a+10, b+10, c+10}}
            {}
    } mFoo(1, 2, 3);

    return 0;
}

...result in this compiler error...

>g++ -std=c++0x main.cpp
main.cpp: In constructor ‘main()::Foo::Foo(int, int, int)’:
main.cpp:18: error: bad array initializer
>

...whereas this...

#include <iostream>

int main()
{
    struct Foo
    {
        public:
            struct Bar
            {
                public:
////////////////////Bar(int a, int b, int c){}

                    int ma, mb, mc;
            } mBar[2];

            Foo(int a, int b, int c)
            : mBar{{a, b, c},
                   {a+10, b+10, c+10}}
            {}
    } mFoo(1, 2, 3);

    return 0;
}

...does not...

>g++ -std=c++0x main.cpp
>

...whereas if I compile the first version of the above code with a different compiler, it compiles...

>/opt/mv_7/arm/tools/arm-gnu/bin/arm-montavista-linux-gnueabi-g++ -std=c++0x main.cpp
>

?
I'd be very grateful for clarity on this. I thought I'd come to understand initializer lists because the first stab at this topic was with the cross-compiler (that compiled the first version of code with no complaints), but the above discrepancy has me puzzled now. Thank you.

Answer 1

In the comments you indicated that you were using gcc 4.4.7.

This is a relatively old compiler. I had no issues compiling the given code using gcc 5.3.1 in -std=c++14 mode.

If this code does not compile with the -std=c++11 flag with your compiler, it's because this older compiler hasn't yet fully implemented the C++1x standard.