当返回对象的函数在没有 return 语句的情况下结束时会发生什么

2021-12-11 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 return 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 返回语句[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价于没有操作数的 return.否则，从 main (basic.start.main) 导致未定义行为.

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，比如 Clang:

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

警告:控制到达非空函数结束[-Wreturn-type]

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

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