c++ - 将 `nullptr` 分配给 `bool` 类型。哪个编译器是正确的？

Question

我有以下代码片段，将 nullptr 分配给 bool 类型。

#include <iostream>

int main()
{
    bool b = nullptr;
    std::cout << b;
}

在 clang 3.8.0 中工作正常。它给出了输出 0。 Clang Demo

但是g++ 5.4.0报错:

source_file.cpp: In function ‘int main()’:
source_file.cpp:5:18: error: converting to ‘bool’ from ‘std::nullptr_t’ requires direct-initialization [-fpermissive]
         bool b = nullptr;

哪个编译器是正确的？

Answer 1

来自 C++ 标准(4.12 boolean 转换)

1 A prvalue of arithmetic, unscoped enumeration, pointer, or pointer to member type can be converted to a prvalue of type bool. A zero value, null pointer value, or null member pointer value is converted to false; any other value is converted to true. For direct-initialization (8.5), a prvalue of type std::nullptr_t can be converted to a prvalue of type bool; the resulting value is false.

所以这个声明

bool b( nullptr );

有效且这个

bool b = nullptr;

错了。

我自己已经在 isocpp 指出了这个问题