How to make [std::operator""s] visible in a namespace?

Question

#include <chrono>

namespace X
{
using namespace std;
struct A
{
    std::chrono::seconds d = 0s; // ok
};
}

namespace Y
{
struct B
{
    std::chrono::seconds d = 0s; // error
};
}

The error message is:

error : no matching literal operator for call to 'operator""s' with argument of type 'unsigned long long' or 'const char *', and no matching literal operator template std::chrono::seconds d = 0s;

My question is:

I don't want to use namespace std; in namespace Y; then, how should I make std::operator""s visible in namespace Y?

score 16 · Accepted Answer · edited May 23 '17 at 10:30

16

If you want to have all the chrono literals then you can use

using namespace std::chrono_literals;

If you just want operator""s then you can use

using std::chrono_literals::operator""s;

Do note that at least on coliru gcc issues a warning for the above line but clang does not. To me there should be no warning. I have asked a follow up question about this at Should a using command issue a warning when using a reserved identifier?

edited May 23 '17 at 10:30

Community

1
1

answered Jan 03 '17 at 13:05

NathanOliver

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I think you need `using namespace ...;` for the first, the second one issue a warning on g++. – Holt Jan 03 '17 at 13:10
@Holt I think that is a gcc bug. Yes it is a reserved name but we are not defining it, just using it so it should be okay. I just added a note about that and that clang does not warn. – NathanOliver Jan 03 '17 at 13:11
This is meant to be used as `using namespace std::chrono_literals;`. The `literals::` part is redundant. – T.C. Jan 03 '17 at 18:50
@T.C. Good point. I forgot you could drop the `literal` namespace. – NathanOliver Jan 03 '17 at 18:54

score 3 · Answer 2 · answered Jun 16 '20 at 14:41

tl;dr: Use

using namespace std::string_literals

These operators are declared in the namespace std::literals::string_literals, where both literals and string_literals are inline namespaces. Access to these operators can be gained with using namespace std::literals, using namespace std::string_literals, and using namespace std::literals::string_literals.

Source: https://en.cppreference.com/w/cpp/string/basic_string/operator%22%22s

How to make [std::operator""s] visible in a namespace?

2 Answers2