Partial implementation of N3665. This paper was not voted into the C++1y draft. However I was looking at it and with some experimentation realized that I could partially implement it, and at the same time offer a performance optimization to cout. I simply added an xsputn override to the cout filebuf. The override does nothing special at all if there is a non-trivial codecvt installed. However if the codecvt returns true for always_noconv(), then this function can dump an entire string to fwrite, instead of doing it a character at a time under overflow(). This just makes sense. I stopped short of a full implementation of N3665 because in order to do so, xsputn would have to allocate a buffer when always_noconv() returned false, and I don't want to go to that expense.

llvm-svn: 188077
This commit is contained in:
Howard Hinnant 2013-08-09 16:25:43 +00:00
parent c65848caa5
commit d7cda0680a
1 changed files with 14 additions and 0 deletions

View File

@ -233,6 +233,7 @@ public:
protected: protected:
virtual int_type overflow (int_type __c = traits_type::eof()); virtual int_type overflow (int_type __c = traits_type::eof());
virtual streamsize xsputn(const char_type* __s, streamsize __n);
virtual int sync(); virtual int sync();
virtual void imbue(const locale& __loc); virtual void imbue(const locale& __loc);
@ -308,6 +309,19 @@ __stdoutbuf<_CharT>::overflow(int_type __c)
return traits_type::not_eof(__c); return traits_type::not_eof(__c);
} }
template <class _CharT>
streamsize
__stdoutbuf<_CharT>::xsputn(const char_type* __s, streamsize __n)
{
if (__always_noconv_)
return fwrite(__s, sizeof(char_type), __n, __file_);
streamsize __i = 0;
for (; __i < __n; ++__i, ++__s)
if (overflow(traits_type::to_int_type(*__s)) == traits_type::eof())
break;
return __i;
}
template <class _CharT> template <class _CharT>
int int
__stdoutbuf<_CharT>::sync() __stdoutbuf<_CharT>::sync()