当返回对象的函数在没有返回语句的情况下结束时会发生什么

2022-01-19 00:00:00 function return object language-lawyer c++

在 C++ 中，当一个应该返回对象的函数在没有返回语句的情况下结束时会发生什么?返回什么?

In C++, what happens when a function that is supposed to return an object ends without a return statement? What gets returned?

例如

std::string func() {}

推荐答案

返回什么?

我们不知道.根据标准，行为是未定义的.

We don't know. According to the standard, the behavior is undefined.

§6.6.3/2 返回声明[stmt.return]:

(强调我的)

从构造函数、析构函数或具有 cv void 返回类型的函数的末尾流出等效于没有操作数的 return.否则，从 main (basic.start.main) 导致未定义的行为.

Flowing off the end of a constructor, a destructor, or a function with a cv void return type is equivalent to a return with no operand. Otherwise, flowing off the end of a function other than main (basic.start.main) results in undefined behavior.

事实上，大多数编译器都会给出警告，例如 Clang:

In fact most compilers would give a warning for it, like Clang:

警告:控制到达非空函数的结尾 [-Wreturn-type]

warning: control reaches end of non-void function [-Wreturn-type]

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