I Want to Convert Std::String into a Const Wchar_T *

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

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*.

char* to const wchar_t * conversion

What's the type of getIpAddress()?

Here's a snippet showing how to convert a string to a wstring (using standard C++11, no error checking):

wstring to_wstring(string const& str)
{
  size_t len = mbstowcs(nullptr, &str[0], 0);
  if (len == -1) // invalid source str, throw
  wstring wstr(len, 0);
  mbstowcs(&wstr[0], &str[0], wstr.size());
  return wstr;
}

Unexpected results with wchar_t and c_str string conversion

Each time you call GetWideString(), you are creating a new std::wstring, which has a newly allocated memory buffer. You are comparing pointers to different memory blocks (assuming Assert::AreEqual() is simply comparing the pointers themselves and not the contents of the memory blocks that are being pointed at).

Update: const wchar_t* wchar2 = GetWideString("me").c_str(); does not work because GetWideString() returns a temporary std::wstring that goes out of scope and gets freed as soon as the statement is finished. Thus you are obtaining a pointer to a temporary memory block, and then leaving that pointer dangling when that memory gets freed before you can use the pointer for anything.

Also, const wchar_t* wchar2 = GetWChar("me"); should not compile. GetWChar() returns a std::wstring, which does not implement an implicit conversion to wchar_t*. You have to use the c_str() method to get a wchar_t* from a std::wstring.

How to make String to const wchar_t* conversion function work under Windows and Linux

In my opinion, there are 2 ways :

1. convert QString to wchar_t* when needed
2. Let QString to store wchar_t* and return QString::unicode directly

These two functions can convert a QString to std::string and std::wstring

QString::toStdWString

QString::toStdString

To build QString as ucs4 :

#define QT_QSTRING_UCS_4
#include "qstring.h"

This can be used in qt3(qstring.h). I can't find the source of qt4.

How to convert a std::string to L data type

auto is not a data-type. It is a placeholder that gets deduced depending on the initializer used.

In your case, the initializer is a wide string-literal of type const wchar_t[size], which decays to const wchar_t* when used to initialize the variable.

A wide string can be stored in a std::wstring.

How to convert a std::string (a narrow string) to a wide string depends on the source's character encoding.

Anyway, there are many others who asked that too:

C++ Convert string (or char*) to wstring (or wchar_t*)

wcscpy_s not affecting wchar_t*

Try something more like this:

struct datum {
    wchar_t*    name;
    wchar_t*    lore;
};

wchar_t* widen(const char *str)
{
    wchar_t *wBuffer = NULL;
    size_t len = strlen(str) + 1;
    size_t wlen = 0;
    mbstowcs_s(&wlen, NULL, 0, str, len);
    if (wlen)
    {
        wBuffer = new wchar_t[wlen];
        mbstowcs_s(NULL, wBuffer, wlen, str, len);
    }
    return wBuffer;
}

datum thisDatum;
thisDatum.name = widen((const char*)sqlite3_column_text(pStmt, 1));
thisDatum.lore = widen((const char*)sqlite3_column_text(pStmt, 2));
...
delete[] thisDatum.name;
delete[] thisDatum.lore;

That being said, I would use std::wstring instead:

struct datum {
    std::wstring    name;
    std::wstring    lore;
};

#include <locale>
#include <codecvt>

std::wstring widen(const char *str)
{
    std::wstring_convert< std::codecvt<wchar_t, char, std::mbstate_t> > conv;
    return conv.from_bytes(str);
}

datum thisDatum;
thisDatum.name = widen((const char*)sqlite3_column_text(pStmt, 1));
thisDatum.lore = widen((const char*)sqlite3_column_text(pStmt, 2));

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