On 2013/01/16 14:14, Denis Krjuchkov <[email protected]> wrote:
> 16.01.2013 19:00, Max Kellermann ??????????:
> >First you map UTF-8 to filesystem path (e.g. via map_uri_fs()), which
> >duplicates the string. Then for conversion to your path class (for
> >passing to a system call), std::string duplicates the string again.
> >Makes two allocations instead of one, even on sane operating systems.
>
> OK. This doubles the copying. But what if we don't adopt std::string
> and use custom memory management? This would allow transfer of
> ownership of allocated string from character conversion routine to
> our wrapper. I think this still gives some protection because it
> would be clearly noticeable if such string is going to be combined
> with char* string which might have other encoding. Don't you agree?
Why custom memory management, when std::string already does all we
need? Transfer of ownership is std::move(). But only if internal
path names are already in std::string, which was my suggestion.
But it's even easier; with my idea, you don't need to transfer
ownership at all. Let some code do the talking:
class Path : private std::string { ... };
(Base class is "private" so you can't accidently cast to a "normal"
std::string.)
Then you have a portability library which overloads some system calls:
static inline FILE *fopen(const Path &path) { return fopen(path.c_str()); }
No overhead here.
On Windows, this function resolves to this instead:
FILE *fopen(const Path &path) {
SystemPath system_path(path);
return fopen(system_path.c_str());
}
Some overhead on Windows.
Next step:
#ifdef WIN32
class Path : private std::wstring { ... };
static inline FILE *fopen(const Path &path) {
return _wfopen(system_path.c_str());
}
#endif
This eliminates the remaining overhead on Windows.
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