I want to convert std::string into a const wchar_t *

Question

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?

Extortionary

Answer 1

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*.

Decembrist

@ʎǝʞuoɯɹǝqʎɔ: You mean wstring var = L"text"; – Sporocyst

Answer 2

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.

Uneducated

This should work fine 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. – Decembrist

You should use MultiByteToWideChar with correct codepage. To be precise, two calls to it are needed: the first to get the required length of the target wchar_t string and the second to convert the char string to the wchar_t string. – Cray

It will only work if wchar_t is Unicode and char is Latin-1 or ASSCII. The first 256 character values of Unicode exactly match Latin-1; the first 128 characters of Latin-1 exactly match ASCII. – Kootenay

This was the quick fix I needed for my situation. Thanks! – Ectomorph

cannot convert ‘const char*’ to ‘wchar_t*’ – Dachi

this gives me an error: cannot convert from 'const wchar_t *' to 'wchar_t *' I had to use: const wchar_t* widecstr = widestr.c_str(); – Diaspore

@MattDillard If this answer is wrong, you could post a correct one ... – Punishment

@Punishment - I did, 14 years ago... :-) – Decembrist

Answer 3

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.

Brilliancy

You probably want CA2CW. You might also want to add a basic explanation for the macro naming convention (eg: Const Ascii -> Const Wchar). – Lovage

There is no CA2CW conversion function. There is a CA2CT version but this simply calls CA2W. See <atlconv.h> for a full list. – Brilliancy

Incredibly useful. In my case, only #include <atlstr.h> worked, while #include <atlconv.h> didn't. Dunno why. – Costotomy

I would also recommend CA2WEX instead, which bypasses potential stack overruns. – Sporocyst

Answer 4

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.

Hammock

I believe those are in C standard; either way, they're in Windows too: msdn.microsoft.com/en-us/library/k1f9b8cy.aspx – Sporocyst

Answer 5

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();

Gouty

Answer 6

If one can use CString, leveraging CString::GetString() would be convenient.

    #include <atlstr.h> // to use CString.
    std::string s = "std::string 한글";
    std::wstring ws = static_cast<CString>(s.c_str()).GetString();

E.g. using MFC in Windows,

    std::string s = "std::string 한글";

    std::wstring ws1 = std::wstring(s.cbegin(), s.cend()); // Uh-oh.
    ::AfxMessageBox(ws1.c_str()); // does NOT print correctly.

    std::wstring ws2 = static_cast<CString>(s.c_str()).GetString();
    ::AfxMessageBox(ws2.c_str()); // prints correctly.
    
    // some more examples.
    ::AfxMessageBox(static_cast<CString>(s.c_str()).GetString()); // prints correctly. 
    ::AfxMessageBox(static_cast<CString>(s.c_str())); // Also works without GetString().
    
    // this is fine.
    std::wstring ws3 = L"std::wstring 한글";
    ::AfxMessageBox(ws3.c_str()); // prints correctly.

Ferocious