How can I convert a Unicode string to a char* or char* const in embarcadero c++ ?
String text = "Hello world";
char *txt = AnsiString(text).c_str();
Older text.t_str() is now AnsiString(String).c_str()
"Unicode string" really isn't specific enough to know what your source data is, but you probably mean 'UTF-16 string stored as wchar_t array' since that's what most people who don't know the correct terminology use.
"char*" also isn't enough to know what you want to target, although maybe "embarcadero" has some convention. I'll just assume you want UTF-8 data unless you mention otherwise.
Also I'll limit my example to what works in VS2010
// your "Unicode" string
wchar_t const * utf16_string = L"Hello, World!";
// #include <codecvt>
std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>,wchar_t> convert;
std::string utf8_string = convert.to_bytes(utf16_string);
This assumes that wchar_t strings are UTF-16, as is the case on Windows, but otherwise is portable code.
You can reinterpret any array as an array of char pointers legally. So if your Unicode data comes in 4-byte code units like
char32_t data[100];
then you can access it as a char array:
char const * p = reinterpret_cast<char const*>(data);
for (std::size_t i = 0; i != sizeof data; ++i)
{
std::printf("Byte %03zu is 0x%02X.\n", i, p[i]);
}
That way, you can examine the individual bytes of your Unicode data one by one.
(That has of course nothing to do with converting the encoding of your text. For that, use a library like iconv or ICU.)
If you work with Windows:
//#include <windows.h>
u16string utext = u"объява";
char text[0x100];
WideCharToMultiByte(CP_UTF8,NULL,(const wchar_t*)(utext.c_str()),-1,text,-1,NULL,NULL);
cout << text;
We can't use std::wstring_convert, wherefore is not available in MinGW 4.9.2.
Related
Is there any method?
My computer is AMD64.
::std::string str;
BOOL loadU(const wchar_t* lpszPathName, int flag = 0);
When I used:
loadU(&str);
the VS2005 compiler says:
Error 7 error C2664:: cannot convert parameter 1 from 'std::string *__w64 ' to 'const wchar_t *'
How can I do it?
First convert it to std::wstring:
std::wstring widestr = std::wstring(str.begin(), str.end());
Then get the C string:
const wchar_t* widecstr = widestr.c_str();
This only works for ASCII strings, but it will not work if the underlying string is UTF-8 encoded. Using a conversion routine like MultiByteToWideChar() ensures that this scenario is handled properly.
If you have a std::wstring object, you can call c_str() on it to get a wchar_t*:
std::wstring name( L"Steve Nash" );
const wchar_t* szName = name.c_str();
Since you are operating on a narrow string, however, you would first need to widen it. There are various options here; one is to use Windows' built-in MultiByteToWideChar routine. That will give you an LPWSTR, which is equivalent to wchar_t*.
You can use the ATL text conversion macros to convert a narrow (char) string to a wide (wchar_t) one. For example, to convert a std::string:
#include <atlconv.h>
...
std::string str = "Hello, world!";
CA2W pszWide(str.c_str());
loadU(pszWide);
You can also specify a code page, so if your std::string contains UTF-8 chars you can use:
CA2W pszWide(str.c_str(), CP_UTF8);
Very useful but Windows only.
If you are on Linux/Unix have a look at mbstowcs() and wcstombs() defined in GNU C (from ISO C 90).
mbs stand for "Multi Bytes String" and is basically the usual zero terminated C string.
wcs stand for Wide Char String and is an array of wchar_t.
For more background details on wide chars have a look at glibc documentation here.
Need to pass a wchar_t string to a function and first be able to create the string from a literal string concantenated with an integer variable.
The original string looks like this, where 4 is the physical drive number, but I want that to be changeable to match whatever drive number I want to pass to the function
auto TargetDrive = L"\\\\.\\PhysicalDrive4";
The following works
int a = 4;
std::string stddrivestring = "\\\\.\\PhysicalDrive" + to_string(a);
std::wstring widedrivestring = std::wstring(stddrivestring.begin(), stddrivestring.end());
const wchar_t* TargetDrive = widedrivestring.c_str();
How do you use unicode in C++ ?
Im aware of wchar_t and wchar_t* but I want to know how you can assign value using only Unicode Values, similar to the way a character can be assigned by equating the variable to the ASCII value:
char a = 92;
Im uysing the MinGW compiler, if it makes a difference.
It can be as simple as:
wchar_t a=L'a';
wchar_t hello_world[]=L"Hello World";
// Or if you really want it to be (old school) C++ and not C
std::wstring s(L"Hello World");
// Or if you want to (be bleeding edge and) use C++11
std::u16string s16(u"Hello World");
std::u32string s32(U"Hello World for the ∞ᵗʰ time");
Exactly the same way:
wchar_t a = 97;
wchar_t xi = 0x03be; // ξ
I am trying to compare two formats that I expected would be somewhat compatible, since they are both generally strings. I have tried to perform strcmp with a string and std::wstring, and as I'm sure C++ gurus know, this will simply not compile. Is it possible to compare these two types? Is there an easy conversion here?
You need to convert your char* string - "multibyte" in ISO C parlance - to a wchar_t* string - "wide character" in ISO C parlance. The standard function that does that is called mbstowcs ("Multi-Byte String To Wide Character String")
NOTE: as Steve pointed out in comments, this is a C99 function and thus is not ISO C++ conformant, but may be supported by C++ implementations as an extension. MSVC and g++ both support it.
It is used thus:
const char* input = ...;
std::size_t output_size = std::mbstowcs(NULL, input, 0); // get length
std::vector<wchar_t> output_buffer(output_size);
// output_size is guaranteed to be >0 because of \0 at end
std::mbstowcs(&output_buffer[0], input, output_size);
std::wstring output(&output_buffer[0]);
Once you have two wstrings, just compare as usual. Note that this will use the current system locale for conversion (i.e. on Windows this will be the current "ANSI" codepage) - normally this is just what you want, but occasionally you'll need to deal with a specific encoding, in which case the above won't do, and you'll need to use something like iconv.
EDIT
All other answers seem to go for direct codepoint translation (i.e. the equivalent of (wchar_t)c for every char c in the string). This may not work for all locales, but it will work if e.g. your char are all ASCII or Latin-1, and your wchar_t are Unicode. If you're sure that's what you really want, the fastest way is actually to avoid conversion altogether, and to use std::lexicographical_compare:
#include <algorithm>
const char* s = ...;
std::wstring ws = ...;
const char* s_end = s + strlen(s);
bool is_ws_less_than_s = std::lexicographical_compare(ws.begin, ws.end(),
s, s_end());
bool is_s_less_than_ws = std::lexicographical_compare(s, s_end(),
ws.begin(), ws.end());
bool is_s_equal_to_ws = !is_ws_less_than_s && !is_s_less_than_ws;
If you specifically need to test for equality, use std::equal with a length check:
#include <algorithm>
const char* s = ...;
std::wstring ws = ...;
std::size_t s_len = strlen(s);
bool are_equal =
ws.length() == s_len &&
std::equal(ws.begin(), ws.end(), s);
The quick and dirty way is
if( std::wstring(your_char_ptr_string) == your_wstring)
I say dirty because it will create a temporary string and copy your_char into it. However, it will work just fine as long as you are not in a tight loop.
Note that wstring uses 16 bit characters (i.e unicode - 65536 possible characters) whereas char* tends to be 8 bit characters (Ascii, Latin english only). They are not the same, so wstring-->char* might loose accuracy.
-Tom
First of all you have to ask yourself why you are using std::wstring which is a unicode format with char* (cstring) which is ansi. It is best practice to use unicode because it allows your application to be internationalized, but using a mix doesn't make much sense in most cases. If you want your cstrings to be unicode use wchar_t. If you want your STL strings to be ansi use std::string.
Now back to your question.
The first thing you want to do is convert one of them to match the other datatype.
std::string an std::wstring have the c_str function
here are the function definitions
const char* std::string::c_str() const
const wchar_t* std::wstring::c_str() const
I don't remember off hand how to convert char * to wchar_t * and vice versa, but after you do that you can use strcmp. If you google you'll find a way.
You could use the functions below to convert std::wstring to std::string then c_str will give you char * which you can strcmp
#include <string>
#include <algorithm>
// Prototype for conversion functions
std::wstring StringToWString(const std::string& s);
std::string WStringToString(const std::wstring& s);
std::wstring StringToWString(const std::string& s)
{
std::wstring temp(s.length(),L' ');
std::copy(s.begin(), s.end(), temp.begin());
return temp;
}
std::string WStringToString(const std::wstring& s)
{
std::string temp(s.length(), ' ');
std::copy(s.begin(), s.end(), temp.begin());
return temp;
}
Convert your wstring to a string.
wstring a = L"foobar";
string b(a.begin(),a.end());
Now you can compare it to any char* using b.c_str() or whatever you like.
char c[] = "foobar";
cout<<strcmp(b.c_str(),c)<<endl;
I assumed that std::wstring and std::string both provide more or less the same interface.
So I tried to enable unicode capabilities for our application
# ifdef APP_USE_UNICODE
typedef std::wstring AppStringType;
# else
typedef std::string AppStringType;
# endif
However that gives me a lot of compile errors when -DAPP_USE_UNICODE is used.
It turned out, that the compiler chokes when a const char[] is assigned to std::wstring.
EDIT: improved example by removing the usage of literal "hello".
#include <string>
void myfunc(const char h[]) {
string s = h; // compiles OK
wstring w = h; // compile Error
}
Why does it make such a difference?
Assigning a const char* to std::string is allowed, but assigning to std::wstring gives compile errors.
Shouldn't std::wstring provide the same interface as std::string? At least for such a basic operation as assignment?
(environment: gcc-4.4.1 on Ubuntu Karmic 32bit)
You should do:
#include <string>
int main() {
const wchar_t h[] = L"hello";
std::wstring w = h;
return 0;
}
std::string is a typedef of std::basic_string<char>, while std::wstring is a typedef of std::basic_string<wchar_t>. As such, the 'equivalent' C-string of a wstring is an array of wchar_ts.
The 'L' in front of the string literal is to indicate that you are using a wide-char string constant.
The relevant part of the string API is this constructor:
basic_string(const charT*);
For std::string, charT is char. For std::wstring it's wchar_t. So the reason it doesn't compile is that wstring doesn't have a char* constructor. Why doesn't wstring have a char* constructor?
There is no one unique way to convert a string of char to a string of wchar. What's the encoding used with the char string? Is it just 7 bit ASCII? Is it UTF-8? Is it UTF-7? Is it SHIFT-JIS? So I don't think it would entirely make sense for std::wstring to have an automatic conversion from char*, even though you could cover most cases. You can use:
w = std::wstring(h, h + sizeof(h) - 1);
which will convert each char in turn to wchar (except the NUL terminator), and in this example that's probably what you want. As int3 says though, if that's what you mean it's most likely better to use a wide string literal in the first place.
To convert from a multibyte encoding to a wide character encoding, take a look at the header <locale> and the type std::codecvt. The Dinkumware library has a class Dinkum::wstring_convert that makes performing such multibyte-to-wide conversions easier.
The function std::codecvt_byname allows one to find a codecvt instance for a particular named encoding. Unfortunately, discovering the names of the encodings (or locales) on your system is implementation-specific.
Small suggestion... Do not use "Unicode" strings under Linux (a.k.a. wide strings). std::string is perfectly fine and holds Unicode very well (UTF-8).
Most Linux API works with char * strings and most popular encoding is UTF-8.
So... Just don't bother yourself using wstring.
In addition to the other answers, you could use a trick from Microsoft's book (specifically, tchar.h), and write something like this:
# ifdef APP_USE_UNICODE
typedef std::wstring AppStringType;
#define _T(s) (L##s)
# else
typedef std::string AppStringType;
#define _T(s) (s)
# endif
AppStringType foo = _T("hello world!");
(Note: my macro-fu is weak, and this is untested, but you get the idea.)
Looks like you can do something like this:
#include <sstream>
// ...
std::wstringstream tmp;
tmp << "hello world";
std::wstring our_string =
Although for a more complex situation, you may want to break down and use mbstowcs
you should use
#include <tchar.h>
tstring instead of wstring/string
TCHAR* instead of char*
and _T("hello") instead of "hello" or L"hello"
this will use the appropriate form of string+char, when _UNICODE is defined.
Is there any method?
My computer is AMD64.
::std::string str;
BOOL loadU(const wchar_t* lpszPathName, int flag = 0);
When I used:
loadU(&str);
the VS2005 compiler says:
Error 7 error C2664:: cannot convert parameter 1 from 'std::string *__w64 ' to 'const wchar_t *'
How can I do it?
First convert it to std::wstring:
std::wstring widestr = std::wstring(str.begin(), str.end());
Then get the C string:
const wchar_t* widecstr = widestr.c_str();
This only works for ASCII strings, but it will not work if the underlying string is UTF-8 encoded. Using a conversion routine like MultiByteToWideChar() ensures that this scenario is handled properly.
If you have a std::wstring object, you can call c_str() on it to get a wchar_t*:
std::wstring name( L"Steve Nash" );
const wchar_t* szName = name.c_str();
Since you are operating on a narrow string, however, you would first need to widen it. There are various options here; one is to use Windows' built-in MultiByteToWideChar routine. That will give you an LPWSTR, which is equivalent to wchar_t*.
You can use the ATL text conversion macros to convert a narrow (char) string to a wide (wchar_t) one. For example, to convert a std::string:
#include <atlconv.h>
...
std::string str = "Hello, world!";
CA2W pszWide(str.c_str());
loadU(pszWide);
You can also specify a code page, so if your std::string contains UTF-8 chars you can use:
CA2W pszWide(str.c_str(), CP_UTF8);
Very useful but Windows only.
If you are on Linux/Unix have a look at mbstowcs() and wcstombs() defined in GNU C (from ISO C 90).
mbs stand for "Multi Bytes String" and is basically the usual zero terminated C string.
wcs stand for Wide Char String and is an array of wchar_t.
For more background details on wide chars have a look at glibc documentation here.
Need to pass a wchar_t string to a function and first be able to create the string from a literal string concantenated with an integer variable.
The original string looks like this, where 4 is the physical drive number, but I want that to be changeable to match whatever drive number I want to pass to the function
auto TargetDrive = L"\\\\.\\PhysicalDrive4";
The following works
int a = 4;
std::string stddrivestring = "\\\\.\\PhysicalDrive" + to_string(a);
std::wstring widedrivestring = std::wstring(stddrivestring.begin(), stddrivestring.end());
const wchar_t* TargetDrive = widedrivestring.c_str();