noexcept operator (since C++11)

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.


noexcept( expression )

Returns a prvalue of type bool.


The noexcept operator does not evaluate expression.

The result is true if the set of potential exceptions of the expression is empty (until C++17)expression is non-throwing (since C++17), and false otherwise.




#include <iostream>
#include <utility>
#include <vector>
void may_throw();
void no_throw() noexcept;
auto lmay_throw = []{};
auto lno_throw = []() noexcept {};
class T
    ~T(){} // dtor prevents move ctor
           // copy ctor is noexcept
class U
    ~U(){} // dtor prevents move ctor
           // copy ctor is noexcept(false)
    std::vector<int> v;
class V
    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'
        // note: the following tests also require that ~T() is noexcept because
        // the expression within noexcept constructs and destroys a temporary
        << "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';  


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) 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)

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