C ++ std :: atomic< bool> :: fetch_还是未实现？ [英] c++ std::atomic<bool>::fetch_or not implemented?

问题描述

具有以下代码摘录：

class myclass {
    volatile std::atomic<bool> flag;
    public:
    myclass(): flag(false) {}
    bool get_flag() { return flag; }
    bool try_set() {
        return !flag.fetch_or(flag, true);
    }
    void reset() {
        flag = false;
    }
};

我遇到此编译错误：

error: ‘volatile struct std::atomic<bool>’ has no member named ‘fetch_or’   
   return !flag.fetch_or(flag, true);

但是，如果我将模板参数更改为 int，则会进行编译：

It compiles if, however, I change the template parameter to int:

class myclass {
    volatile std::atomic<int> flag;
    public:
    myclass(): flag(0) {}
    bool get_flag() { return flag; }
    bool try_set() {
        return !flag.fetch_or(flag, true);
    }
    void reset() {
        flag = 0;
    }
};

atomic 参考文献指出，完全专业化 atomic< bool> 被视为非专业化，相信是问题的根源。所以我的疑问是：

The atomic reference says that "the full specialization atomic<bool>" is treated as "non-specialized", what I believe to be the source of the problems. So my doubts:

1. 如何将完全专业化视为非专业化？


2. 使用标志模板参数 int 代替 bool 调用 flag.fetch_or（）？



1. How can a "full specialization" be "treated as non-specialized"?
2. May there I face any tricky pitfalls using as flag template parameter int instead of bool when calling flag.fetch_or()?

我正在使用gcc 5.1.0，并使用 -std = c ++ 14 进行编译。

I am using gcc 5.1.0, and compiling with -std=c++14.

推荐答案

C ++ 11 N3337草案对于 bool 不需要该方法。

29.5原子类型

template <class T> struct atomic {
  [...]
}

template <> struct atomic<integral> {
  [...]
  integral fetch_or(integral , memory_order = memory_order_seq_cst) noexcept;
  [...]
}

29.5 / 1：

关于原子专业化操作的语义在29.6中定义。

The semantics of the operations on specializations of atomic are defined in 29.6.

29.6.3 / 2对原子类型的算术运算：

29.6.3/2 "Arithmetic operations on atomic types":

在这些函数和函数模板的声明中在专业化方面，积分的名称是指整数类型，而名称atomic-integral的名称是原子的，或者是表145或表146推断的积分的命名基类。

In the declarations of these functions and function template specializations, the name integral refers to an integral type and the name atomic-integral refers to either atomic or to a named base class for integral from Table 145 or inferred from Table 146.

并且表145不包含 bool 。

因此，仅积分（没有 bool ）的专业化 struct 将具有该方法。

So only the integral (without bool) specializations of struct will have that method.

这有点令人困惑，因为在标准的其余部分中，整数类型包括布尔值3.9.1 / 7基本类型：

This is a bit confusing because in the rest of the standard, "integral types" includes bool, 3.9.1/7 "Fundamental types":

键入bool，char，char16_t，char32_t，wcha r_t以及有符号和无符号整数类型统称为整数类型。整数类型的同义词是整数类型。

Types bool, char, char16_t, char32_t, wchar_t, and the signed and unsigned integer types are collectively called integral types. A synonym for integral type is integer type.

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