参数包中的参数计数?这里有一个C ++ 0x std lib函数吗? [英] Count of parameters in a parameter pack? Is there a C++0x std lib function for this?
问题描述
我只是想知道是否有什么C ++ 0x std lib已经可用来计算参数包中的参数数量?我想摆脱下面的代码中的field_count。我知道我可以建立自己的计数器,但它只是似乎这是一个明显的事情,包括在C + + 0x std lib,我想确定它不是已经有:)自己的计数器实现
模板 const tuple< Args ...>数据;
const array< const char *,field_count> source_names;
Entity():data(){
}
};是的,您可以使用。 sizeof ...
。从C ++ 0x FCD(§5.3.3/ 5):
在 sizeof中的标识符。 ..
表达式应命名一个参数包。 sizeof ...
运算符产生为参数包标识符提供的参数数。参数包由 sizeof ...
运算符扩展(14.5.3)。 [示例:
模板< class ... Types&
struct count {
static const std :: size_t value = sizeof ...(Types);
};
- end example ]
< blockquote>
I was just wondering if there was anything in the C++0x std lib already available to count the number of parameters in a parameter pack? I'd like to get rid of the field_count in the code below. I know I can build my own counter, but it just seems like this would be an obvious thing to include in the C++0x std lib, and I wanted to be sure it wasn't already there :) Home-grown counter implementations are most welcome too.
template<const int field_count, typename... Args> struct Entity {
const tuple<Args...> data;
const array<const char*, field_count> source_names;
Entity() : data() {
}
};
解决方案 Yes, you can use sizeof...
. From the C++0x FCD (§5.3.3/5):
The identifier in a sizeof...
expression shall name a parameter pack. The sizeof...
operator yields the number of arguments provided for the parameter pack identifier. The parameter pack is expanded (14.5.3) by the sizeof...
operator. [Example:
template<class... Types>
struct count {
static const std::size_t value = sizeof...(Types);
};
—end example ]
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