UTF-8 everywhere makes a strong case to shun the Microsoft TCHAR, _T(), LPCTSTR and so forth completely, to push wchar_t aside as well, and bravely embrace a world of UTF-8 strings based on a narrow char type.
Which seemed fine until I came to the MFC DDX_Text() macro for getting a CString both in and out of an edit control. Is there any reasonable way to:
Declare CStringA myString intended as an UTF-8 string (or as an ASCII/ANSI string as a degenerate case)
Compile with UNICODE defined
Pass myString through suitable conversions and/or temporary variables and into the third parameter to DDX_Text(), and get sensible results to and from the associated edit control?
If not, how would you recommend handling string input/output via edit controls if your application wanted to use UTF-8 (or ASCII/ANSI in the degenerate case)?
(P.S. this is motivated by Visual Studio 2013 encouraging Unicode-only use of MFC. Given an MFC app, and a desire to use VS2013, this requires UNICODE to be defined... or to cling on to a deprecated way of doing things.)
Windows internally uses UTF-16 as UNICODE standard. So you will have to follow that and use CString which is defined as CStringW in UNICODE. Also you have to use _T() macro. All Windows common controls like Edit Box, List Box, etc are using UNICODE as well.
I'd suggest using UTF-8 for networking stuff only.
// UTF8 conversion
CStringA CUtility::UTF16toUTF8(const CStringW& utf16)
{
return CW2A(utf16, CP_UTF8);
}
CStringW CUtility::UTF8toUTF16(const CStringA& utf8)
{
return CA2W(utf8, CP_UTF8);
}
I am created a library in C++ which exposes c style interface APIs. Some of the arguments are string so they would be char *. Now I know they should be all Unicode but because it is a library I don't think I want to force users to use decide or not. Ideally I thought it would be best to use TCHAR so I can build it either way for unicode code and ASCII users. Than I read this and it opposes the idea in general.
As an example of API, the strings are filenames or error messages like below.
void LoadSomeFile(char * fileName );
const char * GetErrorMsg();
I am using c++ and STL. There is this debate of std::string vs std::wstring as well.
Personally I really like MFC's CString class which takes care of all this nicely but that means I have to use MFC just for its string class.
Now I think TCHAR is probably the best solution for me but do I have to use CString (internally) for that to work? Can I use it with STL string? As far as I can see, it is either string or wstring there.
The TCHAR type is an unfortunate design choice that has thankfully been left behind us. Nobody has to use TCHAR any more, thank goodness. The Unicode choice has been made for us as well: Unicode is the only sane choice going forwards.
The question is, is your library Windows-only? Or is it portable?
If your library is portable, then the typical choice is char * or std::string with UTF-8 encoded strings. For more information, see UTF-8 Everywhere. The summary is that wchar_t is UTF-16 on Windows but UTF-32 everywhere else, which makes it almost useless for cross-platform programming.
If your library runs on Win32 only, then you may feel free to use wchar_t instead. On Windows, wchar_t is UTF-16.
Don't use both, it will make your code and API bloated and difficult to read. TCHAR is a hack for supporting the Win32 API and migrating to Unicode.
I saw on the project properties on Visual Studio 2012 that you can select the Character set for your application.
I use Unicode Character set.
What is the problem with Multi-byte character set? Or better, why should I use the Unicode?
Take for example this piece of code from a DLL that I am doing
RECORD_API int startRecording(
char *cam_name, // Friendly video device name
char *time, // Max time for recording
char *f_width, // Frame width
char *f_height, // Frame height
char *file_path) // Complete output file path
{
...
}
A lot of Unicode functions from Windows.h header use wchar_t parameters; should I use wchar_t also for my functions parameters?
Should I always explicit the W functions (example: ShellExecuteW) ?
First, regardless of what the interface says, the question isn't
Unicode or not, but UTF-16 or UTF-8. Practically speaking, for
external data, you should only use UTF-8. Internally, it
depends on what you are doing. Conversion of UTF-8 to UTF-16 is
an added complication, but for more complex operations, it may
be easier to work in UTF-16. (Although the differences between
UTF-8 and UTF-16 aren't enormous. To reap any real benefits,
you'd have to use UTF-32, and even then...)
In practice, I would avoid the W functions completely, and
always use char const* at the system interface level. But
again, it depends on what you are doing. This is just a general
guideline. For the rest, I'd stick with std::string unless
there was some strong reason not to.
You don't need to explicitly call, the ..W version of a function as this should already be covered by the include files and the settings that you use. So if you compile for Unicodesupport, then the W version of your system call will be used, otherwise the A.
Personally I would only compile for Unicode if you can really test it. At least you shouldn't assume that your application really can work properly in all cases, just because you compiled for it. Compiling for it is only the first step, but of course, you must consequently use the appropriate types and test your code, to be sure that there are no effects you may not have noticed.
I am in the process of developing a small game in DirectX 10 and C++ and I'm finding it hell with the various different types of strings that are required for the various different directx / win32 function calls.
Can anyone recommend which of the various strings are available are the best to use, ideally it would be one type of string that gives a good cast to the other types (LPCWSTR and LPCSTR mostly). Thus far I have been using std::string and std::wstring and doing the .c_str() function to get it in to the correct format.
I would like to get just 1 type of string that I use to pass in to all functions and then doing the cast inside the function.
Use std::wstring with c_str() exactly as you have been doing. I see no reason to use std::string on Windows, your code may as well always use the native UTF-16 encoding.
I would stick to std::wstring as well. If you really need to pass std::string somewhere, you can still convert it on the fly:
std::string s = "Hello, World";
std::wstring ws(s.begin(), s.end());
It works the other way around as well.
If you're using Native COM (the stuff of #import <type_library>), then _bstr_t. It natively typecasts to both LPCWSTR and LPCSTR, and it meshes nicely with COM's memory allocation model. No need for .c_str() calls.
The following may not qualify as a SO question; if it is out of bounds, please feel free to tell me to go away. The question here is basically, "Do I understand the C standard correctly and is this the right way to go about things?"
I would like to ask for clarification, confirmation and corrections on my understanding of character handling in C (and thus C++ and C++0x). First off, an important observation:
Portability and serialization are orthogonal concepts.
Portable things are things like C, unsigned int, wchar_t. Serializable things are things like uint32_t or UTF-8. "Portable" means that you can recompile the same source and get a working result on every supported platform, but the binary representation may be totally different (or not even exist, e.g. TCP-over-carrier pigeon). Serializable things on the other hand always have the same representation, e.g. the PNG file I can read on my Windows desktop, on my phone or on my toothbrush. Portable things are internal, serializable things deal with I/O. Portable things are typesafe, serializable things need type punning. </preamble>
When it comes to character handling in C, there are two groups of things related respectively to portability and serialization:
wchar_t, setlocale(), mbsrtowcs()/wcsrtombs(): The C standard says nothing about "encodings"; in fact, it is entirely agnostic to any text or encoding properties. It only says "your entry point is main(int, char**); you get a type wchar_t which can hold all your system's characters; you get functions to read input char-sequences and make them into workable wstrings and vice versa.
iconv() and UTF-8,16,32: A function/library to transcode between well-defined, definite, fixed encodings. All encodings handled by iconv are universally understood and agreed upon, with one exception.
The bridge between the portable, encoding-agnostic world of C with its wchar_t portable character type and the deterministic outside world is iconv conversion between WCHAR-T and UTF.
So, should I always store my strings internally in an encoding-agnostic wstring, interface with the CRT via wcsrtombs(), and use iconv() for serialization? Conceptually:
my program
<-- wcstombs --- /==============\ --- iconv(UTF8, WCHAR_T) -->
CRT | wchar_t[] | <Disk>
--- mbstowcs --> \==============/ <-- iconv(WCHAR_T, UTF8) ---
|
+-- iconv(WCHAR_T, UCS-4) --+
|
... <--- (adv. Unicode malarkey) ----- libicu ---+
Practically, that means that I'd write two boiler-plate wrappers for my program entry point, e.g. for C++:
// Portable wmain()-wrapper
#include <clocale>
#include <cwchar>
#include <string>
#include <vector>
std::vector<std::wstring> parse(int argc, char * argv[]); // use mbsrtowcs etc
int wmain(const std::vector<std::wstring> args); // user starts here
#if defined(_WIN32) || defined(WIN32)
#include <windows.h>
extern "C" int main()
{
setlocale(LC_CTYPE, "");
int argc;
wchar_t * const * const argv = CommandLineToArgvW(GetCommandLineW(), &argc);
return wmain(std::vector<std::wstring>(argv, argv + argc));
}
#else
extern "C" int main(int argc, char * argv[])
{
setlocale(LC_CTYPE, "");
return wmain(parse(argc, argv));
}
#endif
// Serialization utilities
#include <iconv.h>
typedef std::basic_string<uint16_t> U16String;
typedef std::basic_string<uint32_t> U32String;
U16String toUTF16(std::wstring s);
U32String toUTF32(std::wstring s);
/* ... */
Is this the right way to write an idiomatic, portable, universal, encoding-agnostic program core using only pure standard C/C++, together with a well-defined I/O interface to UTF using iconv? (Note that issues like Unicode normalization or diacritic replacement are outside the scope; only after you decide that you actually want Unicode (as opposed to any other coding system you might fancy) is it time to deal with those specifics, e.g. using a dedicated library like libicu.)
Updates
Following many very nice comments I'd like to add a few observations:
If your application explicitly wants to deal with Unicode text, you should make the iconv-conversion part of the core and use uint32_t/char32_t-strings internally with UCS-4.
Windows: While using wide strings is generally fine, it appears that interaction with the console (any console, for that matter) is limited, as there does not appear to be support for any sensible multi-byte console encoding and mbstowcs is essentially useless (other than for trivial widening). Receiving wide-string arguments from, say, an Explorer-drop together with GetCommandLineW+CommandLineToArgvW works (perhaps there should be a separate wrapper for Windows).
File systems: File systems don't seem to have any notion of encoding and simply take any null-terminated string as a file name. Most systems take byte strings, but Windows/NTFS takes 16-bit strings. You have to take care when discovering which files exist and when handling that data (e.g. char16_t sequences that do not constitute valid UTF16 (e.g. naked surrogates) are valid NTFS filenames). The Standard C fopen is not able to open all NTFS files, since there is no possible conversion that will map to all possible 16-bit strings. Use of the Windows-specific _wfopen may be required. As a corollary, there is in general no well defined notion of "how many characters" comprise a given file name, as there is no notion of "character" in the first place. Caveat emptor.
Is this the right way to write an idiomatic, portable, universal, encoding-agnostic program core using only pure standard C/C++
No, and there is no way at all to fulfill all these properties, at least if you want your program to run on Windows. On Windows, you have to ignore the C and C++ standards almost everywhere and work exclusively with wchar_t (not necessarily internally, but at all interfaces to the system). For example, if you start with
int main(int argc, char** argv)
you have already lost Unicode support for command line arguments. You have to write
int wmain(int argc, wchar_t** argv)
instead, or use the GetCommandLineW function, none of which is specified in the C standard.
More specifically,
any Unicode-capable program on Windows must actively ignore the C and C++ standard for things like command line arguments, file and console I/O, or file and directory manipulation. This is certainly not idiomatic. Use the Microsoft extensions or wrappers like Boost.Filesystem or Qt instead.
Portability is extremely hard to achieve, especially for Unicode support. You really have to be prepared that everything you think you know is possibly wrong. For example, you have to consider that the filenames you use to open files can be different from the filenames that are actually used, and that two seemingly different filenames may represent the same file. After you create two files a and b, you might end up with a single file c, or two files d and e, whose filenames are different from the file names you passed to the OS. Either you need an external wrapper library or lots of #ifdefs.
Encoding agnosticity usually just doesn't work in practice, especially if you want to be portable. You have to know that wchar_t is a UTF-16 code unit on Windows and that char is often (bot not always) a UTF-8 code unit on Linux. Encoding-awareness is often the more desirable goal: make sure that you always know with which encoding you work, or use a wrapper library that abstracts them away.
I think I have to conclude that it's completely impossible to build a portable Unicode-capable application in C or C++ unless you are willing to use additional libraries and system-specific extensions, and to put lots of effort in it. Unfortunately, most applications already fail at comparatively simple tasks such as "writing Greek characters to the console" or "supporting any filename allowed by the system in a correct manner", and such tasks are only the first tiny steps towards true Unicode support.
I would avoid the wchar_t type because it's platform-dependent (not "serializable" by your definition): UTF-16 on Windows and UTF-32 on most Unix-like systems. Instead, use the char16_t and/or char32_t types from C++0x/C1x. (If you don't have a new compiler, typedef them as uint16_t and uint32_t for now.)
DO define functions to convert between UTF-8, UTF-16, and UTF-32 functions.
DON'T write overloaded narrow/wide versions of every string function like the Windows API did with -A and -W. Pick one preferred encoding to use internally, and stick to it. For things that need a different encoding, convert as necessary.
The problem with wchar_t is that encoding-agnostic text processing is too difficult and should be avoided. If you stick with "pure C" as you say, you can use all of the w* functions like wcscat and friends, but if you want to do anything more sophisticated then you have to dive into the abyss.
Here are some things that much harder with wchar_t than they are if you just pick one of the UTF encodings:
Parsing Javascript: Identifers can contain certain characters outside the BMP (and lets assume that you care about this kind of correctness).
HTML: How do you turn 𐀀 into a string of wchar_t?
Text editor: How do you find grapheme cluster boundaries in a wchar_t string?
If I know the encoding of a string, I can examine the characters directly. If I don't know the encoding, I have to hope that whatever I want to do with a string is implemented by a library function somewhere. So the portability of wchar_t is somewhat irrelevant as I don't consider it an especially useful data type.
Your program requirements may differ and wchar_t may work fine for you.
Given that iconv is not "pure standard C/C++", I don't think you are satisfying your own specifications.
There are new codecvt facets coming with char32_t and char16_t so I don't see how you can be wrong as long as you are consistent and pick one char type + encoding if the facets are here.
The facets are described in 22.5 [locale.stdcvt] (from n3242).
I don't understand how this doesn't satisfy at least some of your requirements:
namespace ns {
typedef char32_t char_t;
using std::u32string;
// or use user-defined literal
#define LIT u32
// Communicate with interface0, which wants utf-8
// This type doesn't need to be public at all; I just refactored it.
typedef std::wstring_convert<std::codecvt_utf8<char_T>, char_T> converter0;
inline std::string
to_interface0(string const& s)
{
return converter0().to_bytes(s);
}
inline string
from_interface0(std::string const& s)
{
return converter0().from_bytes(s);
}
// Communitate with interface1, which wants utf-16
// Doesn't have to be public either
typedef std::wstring_convert<std::codecvt_utf16<char_T>, char_T> converter1;
inline std::wstring
to_interface0(string const& s)
{
return converter1().to_bytes(s);
}
inline string
from_interface0(std::wstring const& s)
{
return converter1().from_bytes(s);
}
} // ns
Then your code can use ns::string, ns::char_t, LIT'A' & LIT"Hello, World!" with reckless abandon, without knowing what's the underlying representation. Then use from_interfaceX(some_string) whenever it's needed. It doesn't affect the global locale or streams either. The helpers can be as clever as needed, e.g. codecvt_utf8 can deal with 'headers', which I assume is Standardese from tricky stuff like the BOM (ditto codecvt_utf16).
In fact I wrote the above to be as short as possible but you'd really want helpers like this:
template<typename... T>
inline ns::string
ns::from_interface0(T&&... t)
{
return converter0().from_bytes(std::forward<T>(t)...);
}
which give you access to the 3 overloads for each [from|to]_bytes members, accepting things like e.g. const char* or ranges.