Programming Forums > Application Development > C++

Ancient Dragon · Jun 13th, 2005, 2:06 PM

my VC++ 6.0 MFC program is compiled for UNICODE. I have a std::wstring object that contains a filename. I tried to use wifstream in(filename.c_str()) but got error that the compiler can't convert the first parameter from wchar_t* to char*. Is there another way to do it without explicitly converting it myself? If not, how do people using other languages use anything from the fstream STL library, or is the C-style FILE the only way?

Thanks

Scorpions4ever · Jun 13th, 2005, 4:50 PM

Darn site keeps going up and down. Anyway, one way to do this is to convert the filename to type string like this:

(Toggle Plain Text)

#include <string>
#include <fstream>
#include <iostream>
using namespace std;

int main(void) {
  wstring filename = L"string.cpp";
  string s_filename(filename.begin(), filename.end());
  wifstream in(s_filename.c_str());
  wstring line;
  while (!in.eof()) {
    getline(in, line);
    wcout << line << endl;
  }
  in.close();
  return 0;
}

Ancient Dragon · Jun 13th, 2005, 4:53 PM

I don't want to convert to ascii -- what if the filename is Chinese or Japanese, or some other language that doesn't fit in ascii???

uman · Jun 13th, 2005, 5:01 PM

Does WIndows even allow wide-character filenames?

Scorpions4ever · Jun 13th, 2005, 5:03 PM

BTW, I forgot to mention that the solution above is not necessarily portable either. Also, if the filename is something in japanese or whatever, wifstream fails. Several people have proposed fixes to the STL library for this. Apparently, one of the things holding this up is that several filesystems don't actually support unicode.

Scorpions4ever · Jun 13th, 2005, 5:04 PM

BTW dinkumware (the guys that Microsoft uses for their STL implementation) apparently has a lib that supports wifstream with a wchar_t * filename.

Ancient Dragon · Jun 13th, 2005, 6:34 PM

well, thanks for the comments. Not what I wanted to hear, so I guess I'll have to use wfopen() and associated functions.

Not supporting UNICODE is a lousy excuse for not fixing wifstream() -- there are a lot of other STL unicode classes too, such as wstring that don't work on os without unicode support.

Quote:

Originally Posted by uman

Does WIndows even allow wide-character filenames?

Windows is not the only os that support UNICODE -- *nix and others do too.

obirsoy · Jun 16th, 2005, 3:20 PM

Quote:

Originally Posted by Ancient Dragon

Not supporting UNICODE is a lousy excuse for not fixing wifstream() -- there are a lot of other STL unicode classes too, such as wstring that don't work on os without unicode support.

Windows is not the only os that support UNICODE -- *nix and others do too.

It is not that easy. The below quote is taken from the FAQ of filesystem library in boost. AFAIK POSIX systems do not support wide character file names. They do support UTF-8.

Quote:

Why aren't wide-character names supported? Why not std::wstring or even a templated type?

Wide-character names would provide an illusion of portability where portability does not in fact exist. Behavior would be completely different on operating systems (Windows, for example) that support wide-character names, than on systems which don't (POSIX). Providing functionality that appears to provide portability but in fact delivers only implementation-defined behavior is highly undesirable. Programs would not even be portable between library implementations on the same operating system, let alone portable to different operating systems.

The C++ standards committee Library Working Group discussed this in some detail both on the committee's library reflector and at the Spring, 2002, meeting, and feels that (1) names based on types other than char are extremely non-portable, (2) there are no agreed upon semantics for conversion between wide-character and narrow-character names for file systems which do not support wide-character name, and (3) even the committee members most interested in wide-character names are unsure that they are a good idea in the context of a portable library.

[October, 2002 - PJ Plauger has suggested a locale based conversion scheme. Others have indicated support for such an experiment.]

PJ Plauger is the president(?) of Dinkunware and as far as I can understand that portion of his library is just an experiment to understand the real issues involved in both implementing and using wide character file names.

Ancient Dragon · Jun 16th, 2005, 3:52 PM

That makes no sense -- Windows (and possibly others) have wfopen() which takes a wchar_t* for filename. So why can't fstreams? And from what little I could find about it with google, there is apparently a C ANSI standard for it.

obirsoy · Jun 16th, 2005, 4:34 PM

Looks like today is my quote day :p

This is taken from POSIX standard (IEEE Std 1003.1, 2004 Edition )

Quote:

4.6 Filenames
For a filename to be portable across implementations conforming to IEEE Std 1003.1-2001, it shall consist only of the portable filename character set as defined in Portable Filename Character Set. The hyphen character shall not be used as the first character of a portable filename. Uppercase and lowercase letters shall retain their unique identities between conforming implementations. In the case of a portable pathname, the slash character may also be used.

Quote:

3.276 Portable Filename Character Set
The set of characters from which portable filenames are constructed. A B C D E F G H I J K L M N O P Q R S T U V W X Y Z a b c d e f g h i j k l m n o p q r s t u v w x y z 0 1 2 3 4 5 6 7 8 9 . _ - The last three characters are the period, underscore, and hyphen characters, respectively.

As I see it, having wfopen is just a convience (misleading one I should add)for doing the conversions yourself. Basically do not expect your code to work on different locales, just because you used wfopen.

Are you sure wfopen is a standard function? For example the POSIX standard mentioned above does not contain such a function.

Jun 13th, 2005, 2:06 PM	#1
Ancient Dragon PFO God In Training Join Date: Jun 2005 Location: near St Louis, MO. (USA) Posts: 549 Rep Power: 4	UNICODE and ifstreams my VC++ 6.0 MFC program is compiled for UNICODE. I have a std::wstring object that contains a filename. I tried to use wifstream in(filename.c_str()) but got error that the compiler can't convert the first parameter from wchar_t* to char*. Is there another way to do it without explicitly converting it myself? If not, how do people using other languages use anything from the fstream STL library, or is the C-style FILE the only way? Thanks

Jun 13th, 2005, 4:50 PM	#2
Scorpions4ever Programmer Join Date: Jun 2005 Posts: 86 Rep Power: 4	Darn site keeps going up and down. Anyway, one way to do this is to convert the filename to type string like this: (Toggle Plain Text) #include <string> #include <fstream> #include <iostream> using namespace std; int main(void) { wstring filename = L"string.cpp"; string s_filename(filename.begin(), filename.end()); wifstream in(s_filename.c_str()); wstring line; while (!in.eof()) { getline(in, line); wcout << line << endl; } in.close(); return 0; } #include <string> #include <fstream> #include <iostream> using namespace std; int main(void) { wstring filename = L"string.cpp"; string s_filename(filename.begin(), filename.end()); wifstream in(s_filename.c_str()); wstring line; while (!in.eof()) { getline(in, line); wcout << line << endl; } in.close(); return 0; }

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Jun 13th, 2005, 4:53 PM	#3
Ancient Dragon PFO God In Training Join Date: Jun 2005 Location: near St Louis, MO. (USA) Posts: 549 Rep Power: 4	I don't want to convert to ascii -- what if the filename is Chinese or Japanese, or some other language that doesn't fit in ascii???

Jun 13th, 2005, 5:01 PM	#4
uman Expert Programmer Join Date: Dec 2004 Posts: 794 Rep Power: 4	Does WIndows even allow wide-character filenames?

Jun 13th, 2005, 5:03 PM	#5
Scorpions4ever Programmer Join Date: Jun 2005 Posts: 86 Rep Power: 4	BTW, I forgot to mention that the solution above is not necessarily portable either. Also, if the filename is something in japanese or whatever, wifstream fails. Several people have proposed fixes to the STL library for this. Apparently, one of the things holding this up is that several filesystems don't actually support unicode.

Jun 13th, 2005, 5:04 PM	#6
Scorpions4ever Programmer Join Date: Jun 2005 Posts: 86 Rep Power: 4	BTW dinkumware (the guys that Microsoft uses for their STL implementation) apparently has a lib that supports wifstream with a wchar_t * filename.

Jun 16th, 2005, 3:52 PM	#9
Ancient Dragon PFO God In Training Join Date: Jun 2005 Location: near St Louis, MO. (USA) Posts: 549 Rep Power: 4	That makes no sense -- Windows (and possibly others) have wfopen() which takes a wchar_t* for filename. So why can't fstreams? And from what little I could find about it with google, there is apparently a C ANSI standard for it.

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Programming Forums > Application Development > C++

UNICODE and ifstreams