我目前正在使用非常聪明的包 boost::const_string 直到 http://libcxx.llvm.org/ 已在 Ubuntu 或 GCC 上预打包，使其 __versa_string（在标题中ext/vstring.h）其默认字符串实现。 libcxx 的 std::string 以及 __versa_string 默认使用 _small-string 优化 (SSO)。然而，缺乏对输出到 std::ostream 的默认支持。 除非我们通过 c_str() 强制将 x 转换为 c 字符串，该代码
#include <iostream>
#include <boost/const_string.hpp>
const_string<char> x;
std::cout << x << endl;
才能
std::cout << x.c_str() << endl;
按预期编译和工作。我将以下行添加到 const_string.hpp
template <typename T>
inline std::ostream & operator << (std::ostream & os, const boost::const_string<T> & a)
{
return os.write(a.data(), a.size());
}
这应该会提高 x.c_str() 的性能，因为 size() 已经已知并且不存在需要通过搜索 NULL 来计算，如 c_str() 中。我为我工作，但我不确定它是否适用于所有情况。我错过了什么吗？
I'm currently using the very clever package boost::const_string until http://libcxx.llvm.org/ is available pre-packaged on Ubuntu or GCC make its __versa_string (in header ext/vstring.h) its default string implementation. libcxx's std::string aswell as __versa_string uses _small-string optimization (SSO) by default. Default support for outputting to an std::ostream is lacking however. The code
#include <iostream>
#include <boost/const_string.hpp>
const_string<char> x;
std::cout << x << endl;
does not work unless we force x into a c-string via c_str() which becomes
std::cout << x.c_str() << endl;
which compiles and works as expected. I added the following line to const_string.hpp
template <typename T>
inline std::ostream & operator << (std::ostream & os, const boost::const_string<T> & a)
{
return os.write(a.data(), a.size());
}
This should improve performance over x.c_str() because size() is already known and does not need to be calculated by searching for NULL as in c_str(). I works for me but I am uncertain whether it works all cases. Have I missed something?
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不（你没有错过任何东西，据我所知）。如果您的目标不是复制内容，那么 str.data() 就是正确的选择。
No (you have not missed anything, afaik). If your aim is not to copy over content, str.data() is the way to go.
是的，只需包含
const_string/io.hpp即可。然而它所做的只是：Yes, just include
const_string/io.hpp. All it does however is:看起来，这可能会根据应用于字符串流的区域设置和/或方面与仅编写直接数据而产生影响。
这会降低性能，但是从 const_string 创建 std::string 并使用
<<将其插入到流中怎么样？It seems that this could have implications based on the locale and/or facets applied to the stream for strings vs just writing the straight data as you're doing.
It would be less performant, but what about creating a std::string from the const_string and using
<<to insert that into the stream?