当文件名包含宽字符时使用ifstream

Question

Using C++Builder XE5 (bcc32) in Windows 7.

I am trying to open a file whose filename contains a wide character. The actual filename I'm testing with is C:\\bΛx\\foo.txt . The non-ASCII character there is U+039B .

I have this filename stored correctly in a std::wstring . However, trying:

std::ifstream f( filename.c_str() );

fails to open the file.

Of course, in Standard C++ fopen only takes char * . However, the Dinkumware C++ RTL implementation has an overload accepting wchar_t * . Unfortunately the implementation of that overload in ...\\Embarcadero\\RAD Studio\\12.0\\source\\cpprtl\\Source\\dinkumware\\source\\fiopen.cpp does not call _wfopen . Instead it uses wcstombs to convert the string to UTF-8 and then calls fopen .

Checking the source for fopen , it calls the narrow version of an underlying function ___topen which ultimately passes the UTF-8 string to CreateFile .

When I inspect the attempt to open the file using Sysinternals Process Monitor, it shows that it did attempt to open the file with a UTF-8 file string, and the operating system rejected this with the result NAME COLLISION .

If I open the file using _wfopen( filename.c_str(), L"r" ) then all is well and I can read the file using CI/O functions, but I can't use C++ iostreams of course.

Is there any way to use std::ifstream to open a file with U+039B or other such characters in the filename?

Note that using std::wifstream doesn't work either (it still tries to open the UTF-8 version of the filename).

Answer 1

If I open the file using _wfopen( filename.c_str(), L"r" ) then all is well and I can read the file using CI/O functions, but I can't use C++ iostreams of course.

I don't see that "of course". Your problem is reduced to making an iostreams streambuf from a FILE* . Howard Hinnant answered here that there's no method provided by the Standard, but implementing a streambuf -derived class on top of FILE* is pretty straightforward. He even mentions some code that he feels would be a good starting point.

Note that this only makes sense for a text file. iostreams and binary files do not get along; there's a character encoding layer and ios_base::binary does not turn that off.