问题描述
向量的新方法 data()
提供了一个const和非const版本。
不过string的 data / code>方法只提供一个const版本。
Vector's new method data()
provides a const and non-const version.
However string's data()
method only provides a const version.
我认为他们改变了 std :: string
,以便字符现在需要是连续的(如 std :: vector
)。
I think they changed the wording about std::string
so that the chars are now required to be contiguous (like std::vector
).
code> std :: string :: data 刚刚错过了?或者是只允许const访问字符串底层字符的好理由。
Was std::string::data
just missed? Or is the a good reason to only allow const access to a string's underlying characters?
注意: std :: vector :: data
有另一个不错的功能,它不是未定义的行为调用 data()
在一个空向量。而& vec.front()
是未定义的行为。
note: std::vector::data
has another nice feature, it's not undefined behavior to call data()
on an empty vector. Whereas &vec.front()
is undefined behavior if it's empty.
推荐答案
在C ++ 98/03中,由于字符串常常被实现为COW,因此没有非const data()
的好理由。如果引用计数大于1,则非const data()
将需要一个副本。虽然可能,这在C ++ 98中并不可取/ 03。
In C++98/03 there was good reason to not have a non-const data()
due to the fact that string was often implemented as COW. A non-const data()
would have required a copy to be made if the refcount was greater than 1. While possible, this was not seen as desirable in C++98/03.
2005年10月,委员会在添加了const和非const data()
到 vector
添加const和非const 到
到
映射
。当时, string
没有被更改,因此取缔COW。但后来,通过C ++ 11,COW string
不再符合。 string
spec在C ++ 11中也被收紧,因此它需要是连续的,并且总是有一个由 ](size())
。在C ++ 03中,终止null只是由 operator []
的const重载保证。
In Oct. 2005 the committee voted in LWG 464 which added the const and non-const data()
to vector
, and added const and non-const at()
to map
. At that time, string
had not been changed so as to outlaw COW. But later, by C++11, a COW string
is no longer conforming. The string
spec was also tightened up in C++11 such that it is required to be contiguous, and there's always a terminating null exposed by operator[](size())
. In C++03, the terminating null was only guaranteed by the const overload of operator[]
.
简单来说,对于C ++ 11 string
,非const data()
看起来更合理。据我所知,从未提出过。
So in short a non-const data()
looks a lot more reasonable for a C++11 string
. To the best of my knowledge, it was never proposed.
更新:
charT* data() noexcept;
在作者在2月份的杰克逊维尔会议上。
was added basic_string
in the C++1z working draft N4582 by David Sankel's P0272R1 at the Jacksonville meeting in Feb. 2016.
很好的工作David!
Nice job David!
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