Using std :: hash <std :: thread :: id> () (std :: this_thread :: get_id ())
I am currently working on building a C ++ application on Windows and Linux, during some debugging I found that
std::this_thread::get_id().hash()
does not compile on Linux with gcc 4.8 (thanks to the comments in this thread ). The suggested fix for this was to use:
std::hash<std::thread::id>()(std::this_thread::get_id())
Does anyone know if they produce the same result?
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GCC reserves the right to reject the code. The standard does not define a member hash
for std::thread::id
. C ++ 11, 30.3.1.1:
namespace std {
class thread::id {
public:
id() noexcept;
};
bool operator==(thread::id x, thread::id y) noexcept;
bool operator!=(thread::id x, thread::id y) noexcept;
bool operator<(thread::id x, thread::id y) noexcept;
bool operator<=(thread::id x, thread::id y) noexcept;
bool operator>(thread::id x, thread::id y) noexcept;
bool operator>=(thread::id x, thread::id y) noexcept;
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<< (basic_ostream<charT, traits>& out, thread::id id);
// Hash support
template <class T> struct hash;
template <> struct hash<thread::id>;
}
So using std::hash<std::thread::id>()(std::this_thread::get_id())
is definitely a valid (actually the only valid) way to get a stream ID hash.
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std::thread::id::hash()
not up to standard as far as I can tell. So this is probably an extension or implementation of a part. Thus, his behavior will obviously be implemented.
std::hash<std::thread::id>()(std::this_thread::get_id())
is in the standard.
Since you cannot have a thread on multiple systems, and you cannot call .hash()
in any portable code, what remains is that some platform-specific modules use .hash()
your common code using std::hash
. You can rely on your sanity and believe that .hash()
is the same, or you can sweep your platform module. I would go in a big way.
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