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
{
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'
// 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';
}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
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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https://en.cppreference.com/w/cpp/language/noexcept