convert bitset to string?

What is w开发者_开发知识库rong with this code ?

set<string> nk ;
bitset<3> bs1(string("100"));
nk.insert(bs1.to_string());

error: no matching function for call to `std::bitset<3u>::to_string()'

why?!

UPDATE :

Thansk , this works . But why does it work ? :D

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While checking Space_COwbOy's answer, I found another page that shows that to_string is a template function (with parameters similar to std::basic_string). I haven't tried this, so just check it out.