The specification for vector's move constructor is (copied out of the standard):
vector(vector&&); Notice the lack of noexcept. But both gcc 4.8 and Clang 3.2 report that std::is_nothrow_move_constructible<std::vector<int>>::value returns true (i.e, 1):
#include<vector> #include<iostream> int main() { std::cout << std::is_nothrow_move_constructible<std::vector<int>>::value << '\n'; } What is the cause of this apparent discrepancy?
The standard allows an implementation to strengthen the exception specification of a method as per
17.6.5.12 Restrictions on exception handling [res.on.exception.handling]
4 Destructor operations defined in the C++ standard library shall not throw exceptions. Every destructor in the C++ standard library shall behave as if it had a non-throwing exception specification. Any other functions defined in the C++ standard library that do not have an exception-specification may throw implementation-defined exceptions unless otherwise specified.191 An implementation may strengthen this implicit exception-specification by adding an explicit one.192
vector move constructor is declared noexcept.
vector<vector<int>>::push_back. Said differently, the lack of the noexcept creates a significant performance penalty for cases like this.std::is_nothrow_move_constructible) that vector, list, string, set, multiset, map, and multimap are noexcpt. Clang 3.2 reports that all standard containers are noexcept. VS2013 reports that only string is noexcept.