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noexcept operator (since C++11)

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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.

Contents

[edit] Syntax

noexcept( expression )

Returns a prvalue of type bool.

[edit] 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:

In all other cases the result is true.

[edit] Keywords

noexcept

[edit] Example

#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

[edit] See also

noexcept specifier requires a function to not throw any exceptions (C++11) [edit]
exception specification specifies what exceptions are thrown by a function (deprecated) [edit]