c++ - 如何知道函数何时抛出异常以及何时使用 noexcept

Question

在声明函数时，您可以使用noexcept 说明符来声明该函数不会抛出:

int foo() noexcept
{
  return 10;
}

但是，如何确定函数何时抛出异常？我知道使用 new 运算符可能会抛出 std::bad_alloc，但还有哪些其他表达式/运算符会抛出？有没有办法明确确定它是否会？

Answer 1

but what are some other expressions/operators that can throw?

潜在抛出表达式定义为(根据 cppreference )

An expression e is potentially-throwing if:

• e is a function call to a potentially-throwing function or pointer to function
• e makes an implicit call to a potentially-throwing function (such as an overloaded operator, an allocation function in a new-expression, a constructor for a function argument, or a destructor if e is a full-expression)
• e is a throw-expression
• e is a dynamic_cast that casts a polymorphic reference type
• e is a typeid expression applied to a dereferenced pointer to a polymorphic type
• e has an immediate subexpression that is potentially-throwing

此外，任何具有未定义行为的表达式。

就语言而言，未声明 noexcept 的函数可能会抛出，即使它可能永远不会抛出。

Is there a way to explicitly determine if it will?

通常不会，您无法确定表达式是否会抛出 - 至少在假设 P ≠ NP 的多项式时间内不会。

但是，您可以使用noexcept-expression 确定一个表达式是否潜在抛出:

void foo() noexcept;
void bar() {
    // nothing that might throw
}

std::cout << noexcept(1+1);                        // prints 1
std::cout << noexcept(foo())                       // prints 1
std::cout << noexcept(bar())                       // prints 0
std::cout << noexcept(new char);                   // prints 0
std::cout << noexcept(throw 1);                    // prints 0