Using std::variant in g++

Question

How can I use std::variant in g++? Why isn't there std::variant in std::experimental (though std::optional is)? What version of g++ do I need? I prefer not to use boost and I'd like to use standard library only.

Edit: it seems like only g++ 7 supports std::variant. Then my question is: when will it be released and what problems may I encounter when using its experimental version?

@BasileStarynkevitch what is the version number? How can I get it? — Aleksandr Tukallo, Dec 22 '16 at 13:49
@BasileStarynkevitch I know my version number. I have `g++-6.2` and `g++-5.4`. They do not have `variant` unfortunately — Aleksandr Tukallo, Dec 22 '16 at 13:52

score 5 · Accepted Answer · answered Dec 22 '16 at 13:50

5

This page says, that GCC 7 has std::variant.

answered Dec 22 '16 at 13:50

Ralph Tandetzky

22,780
11
73
120

Yep, I see. How can I install it on Ubuntu? Or as I found out, GCC 7 has not been released yet, when will it be? – Aleksandr Tukallo Dec 22 '16 at 14:44
1

@AleksandrTukallo: Simply with download, configure; make; make install. Works perfect! – Klaus Dec 22 '16 at 14:55
@Klaus thanks! But what problems may I encounter when using it before release? Is it ok? – Aleksandr Tukallo Dec 22 '16 at 14:56
1

@AleksandrTukallo: It is in stage 3 which means that there are a number of open bugs which should be fixed in the next days. Maybe you run into one of them. But I believe that you even run faster in a unfixed bug of an older gcc version as in a new one from current pre release branch. Short answer: Give it a chance! You can have as many versions in parallel as you want. If it do not work: Write a bug report. It will help others! – Klaus Dec 22 '16 at 15:00

score 2 · Answer 2 · answered Dec 22 '16 at 13:10

2

GCC has an info page where you can check which language feature was implemented with which version. It looks like variant is not yet implemented.

answered Dec 22 '16 at 13:10

user2393256

1,001
1
15
26

According to the table `std::optional` is also not implemented, though I can use it in my `g++ 5.4`: [experimental optional](http://en.cppreference.com/w/cpp/experimental/optional/optional). – Aleksandr Tukallo Dec 22 '16 at 13:15
1

There is always [Boost.Variant](http://www.boost.org/doc/libs/1_62_0/doc/html/variant.html) – Martin Bonner supports Monica Dec 22 '16 at 13:16
@user2393256 Does the link list standard library status or only core language features? – Ralph Tandetzky Dec 22 '16 at 13:45

Using std::variant in g++

2 Answers2