C ++ 11运算符“带双参数 [英] C++11 operator"" with double parameter

问题描述

请考虑：

struct str {};

str operator"" _X(long double d) {
    return str();
}

使用g ++进行编译4.7.2 Wall std = c ++ 11

This compiles fine with g++ 4.7.2 Wall std=c++11

但现在如果我给一个double：

but now if I give a double :

str operator"" _X(double d) {
    return str();
}

我收到以下错误信息：
main.cpp | 3 |错误：str运算符_X（双）具有无效的参数列表

I get the following error message: main.cpp|3|error: 'str operator"" _X(double)' has invalid argument list

有什么问题？这有什么关系不可能重新定义内置文字后缀的意义（Stroustrup FAQ）？

What is the problem ? Has this something to do with "It is not possible to redefine the meaning of a built-in literal suffix" (Stroustrup FAQ) ? Can you think of a workaround ?

推荐答案

问题是什么？ p>

What is the problem?

问题是，标准禁止它。根据用户定义文字的C ++ 11标准的第13.5.8./3节：

The problem is that the Standard forbids it. Per paragraph 13.5.8./3 of the C++11 Standard on user-defined literals:

文字操作符的声明有一个等价于
之一的参数声明子句：

The declaration of a literal operator shall have a parameter-declaration-clause equivalent to one of the following:

const char*
unsigned long long int
long double
char
wchar_t
char16_t
char32_t
const char*, std::size_t
const wchar_t*, std::size_t
const char16_t*, std::size_t
const char32_t*, std::size_t

关于解决方法，我不确定是否需要，因为下面的工作正常（ double 到 long double ，因此您可以传递 double 类型的文字：

Concerning a workaround, I am not sure it is needed, since the following works fine (a double gets implicitly converted to a long double, so you can pass in literals of type double):

struct str {};

str operator"" _X(long double d) {
    return str();
}

int main()
{
    str s = 4.0_X;
}

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