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noexcept specifier (a partir do C++ 11)

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Specifies whether a function will throw exceptions or not.

Índice

[editar] Sintaxe

noexcept (1)
noexcept(expression) (2)

[editar] Explicação

If the value of the constant expression is true, the function is declared to not throw any exceptions. noexcept without a constant expression is equivalent to noexcept(true).

One of the uses of the constant expression is (along with the Operador NJ) to define templated functions that declare noexcept for some types but not others.

Note that a noexcept specification on a function is not a compile-time check; it is merely a method for a programmer to inform the compiler whether or not a function should throw exceptions. The compiler can use this information to enable certain optimizations on non-throwing functions as well as enable the Operador NJ, which can check at compile time if a particular expression is declared to throw any exceptions. For example, containers such as std::vector will move their elements if the elements' move constructor is noexcept, and copy otherwise.

If a function marked noexcept allows an uncaught exception to escape at runtime, std::terminate is called immediately.

[editar] Deprecates

noexcept is an improved version of throw(), which is deprecated in C++11. Unlike throw(), noexcept will not call std::unexpected and may or may not unwind the stack, which potentially allows the compiler to implement noexcept without the runtime overhead of throw().

[editar] Palavras-chave

noexcept

[editar] Exemplo

// whether foo is declared noexcept depends on if the expression
// T() will throw any exceptions
template <class T>
  void foo() noexcept(noexcept(T())) {}
void bar() noexcept(true) {}
void baz() noexcept { throw 42; }  // noexcept is the same as noexcept(true)
 
int main() 
{
    foo<int>();  // noexcept(noexcept(int())) => noexcept(true), so this is fine
 
    bar();  // fine
    baz();  // compiles, but at runtime this calls std::terminate
}


[editar] Veja também

noexcept operador determines if an expression throws any exceptions (a partir do C++ 11) [edit]
especificação de exceção
especifica que as exceções são lançadas por um (obsoleta) função
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specifies what exceptions are thrown by a function (obsoleta)
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[edit]
jogar expressão
sinais de um erro e transfere o controle para o manipulador de erro
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signals an error and transfers control to error handler
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[edit]
obtém uma referência rvalue se o construtor movimento não joga
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obtains an rvalue reference if the move constructor does not throw
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(modelo de função) [edit]