Difference between revisions of "cpp/language/noexcept"
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Revision as of 22:05, 6 June 2014
The noexcept operator performs a compile-time check that returns true if an expression is declared to not throw any exceptions.
It can be used within a function template's noexcept specifier to declare that the function will throw exceptions for some types but not others.
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Syntax
noexcept( expression )
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Returns a rvalue of type bool.
Explanation
The noexcept operator does not evaluate expression. The result is false if the expression contains at least one of the following potentially evaluated constructs:
- call to any type of function that does not have non-throwing exception specification, unless it is a constant expression.
-
throwexpression. -
dynamic_castexpression when the target type is a reference type, and conversion needs a run time check -
typeidexpression when argument type is polymorphic class type
In all other cases the result is true.
Keywords
Example
Run this code
#include <iostream> #include <utility> #include <vector> void may_throw(); void no_throw() noexcept; auto lmay_throw = []{}; auto lno_throw = []() noexcept {}; class T{ public: ~T(){} // dtor prevents move ctor // copy ctor is noexcept }; class U{ public: ~U(){} // dtor prevents move ctor // copy ctor is noexcept(false) std::vector<int> v; }; class V{ public: std::vector<int> v; }; int main() { T t; U u; V v; std::cout << std::boolalpha << "Is may_throw() noexcept? " << noexcept(may_throw()) << '\n' << "Is no_throw() noexcept? " << noexcept(no_throw()) << '\n' << "Is lmay_throw() noexcept? " << noexcept(lmay_throw()) << '\n' << "Is lno_throw() noexcept? " << noexcept(lno_throw()) << '\n' << "Is ~T() noexcept? " << noexcept(std::declval<T>().~T()) << '\n' << "Is T(rvalue T) noexcept? " << noexcept(T(std::declval<T>())) << '\n' << "Is T(lvalue T) noexcept? " << noexcept(T(t)) << '\n' << "Is U(rvalue U) noexcept? " << noexcept(U(std::declval<U>())) << '\n' << "Is U(lvalue U) noexcept? " << noexcept(U(u)) << '\n' << "Is V(rvalue V) noexcept? " << noexcept(V(std::declval<V>())) << '\n' << "Is V(lvalue V) noexcept? " << noexcept(V(v)) << '\n'; }
Output:
Is may_throw() noexcept? false Is no_throw() noexcept? true Is lmay_throw() noexcept? false Is lno_throw() noexcept? true Is ~T() noexcept? true Is T(rvalue T) noexcept? true Is T(lvalue T) noexcept? true Is U(rvalue U) noexcept? false Is U(lvalue U) noexcept? false Is V(rvalue V) noexcept? true Is V(lvalue V) noexcept? false
See also
noexcept specifier(C++11)
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specifies whether a function could throw exceptions |
| Dynamic exception specification(until C++17) | specifies what exceptions are thrown by a function (deprecated in C++11) |
