《C++笔记》 Part14 MFC的String to CString 转换在多语言系统下乱码问题

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Summary

Encountered problem in convert from string to CString (LPCWSTR), and the reverse convert, find out the way to convert between these two types and tested in Visual Studio with successful result. The unicode setting is configured in the Visual Studio project property page –> Configuration Properties –> General –> Character Set –> Use Unicode Character Set, as below picture shows,

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Different string types description as below, as How to convert std::string to LPCSTR? mentioned,

• LPSTR - (long) pointer to string - char *
• LPCSTR - (long)pointer to constant string - const char *
• LPWSTR - (long) pointer to Unicode (wide) string - wchar_t *
• LPCWSTR - (long) pointer to constant Unicode (wide) string - const wchar_t*
• LPTSTR - (long) pointer to TCHAR (Unicode if UNICODE is defined, ANSI if not) string - TCHAR *
• LPCTSTR - (long) pointer to constant TCHAR string - const TCHAR *

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C++ convert from string to LPCWSTR

As you know, std::string is char* type, while LPCWSTR ,LPWSTR or CString is wchar_t* as long as the Visual Studio configured as Unicode Character Set.

I am using How to convert std::string to LPCSTR? solution as below code solved this problem,

LPWSTR ConvertString(const std::string& instr)
{
    // Assumes std::string is encoded in the current Windows ANSI codepage
    int bufferlen = ::MultiByteToWideChar(CP_ACP, 0, instr.c_str(), instr.size(), NULL, 0);

    if (bufferlen == 0)
    {
        // Something went wrong. Perhaps, check GetLastError() and log.
        return 0;
    }

    // Allocate new LPWSTR - must deallocate it later
    LPWSTR widestr = new WCHAR[bufferlen + 1];

    ::MultiByteToWideChar(CP_ACP, 0, instr.c_str(), instr.size(), widestr, bufferlen);

    // Ensure wide string is null terminated
    widestr[bufferlen] = 0;

    // Do something with widestr
    return widestr;
    //delete[] widestr;
}

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Refer to the How to convert string to LPCTSTR? solution 5, it is the similar solution as above by using MultiByteToWideChar function,

//该转换方式可解决英文及其它语言系统中文字符乱码问题—解决方法一
USES_CONVERSION;
std::wstring s2ws(const std::string& s)
{
 int len;
 int slength = (int)s.length() + 1;
 len = MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, 0, 0);
 wchar_t* buf = new wchar_t[len];
 MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, buf, len);
 std::wstring r(buf);
 delete[] buf;
 return r;
}

std::string s;

#ifdef UNICODE
std::wstring stemp = s2ws(s); // Temporary buffer is required
LPCWSTR result = stemp.c_str();
#else
LPCWSTR result = s.c_str();
#endif>

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C++ convert from LPCWSTR to string

To convert from LPCWSTR to string, can split into two steps, first step convert from CString to wchar_t, 2nd step, convert from wchar_t to char*, as below code shows,

 //convert from CString to char* , first from CString to wchar_t then to char *
    wchar_t wCharString = sFile.GetBuffer(sFile.GetLength()+1); //CString to wchar_t
    size_t origsize = wcslen(wCharString) + 1;
    size_t convertedChars = 0;
    char gszFile[100] = {0};
    wcstombs_s(&convertedChars, gszFile, origsize, wCharString , _TRUNCATE); //from wchar_t to char*

Below code from MSDN is working perfectly for the conversion from wchar_t* to char* by using wcstombs_s function,

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// crt_wcstombs_s.c
// This example converts a wide character
// string to a multibyte character string.
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

#define BUFFER_SIZE 100

int main( void )
{
    size_t   i;
    char      *pMBBuffer = (char *)malloc( BUFFER_SIZE );
    wchar_t*pWCBuffer = L"Hello, world.";

    printf( "Convert wide-character string:\n" );

    // Conversion
    wcstombs_s(&i, pMBBuffer, (size_t)BUFFER_SIZE, 
               pWCBuffer, (size_t)BUFFER_SIZE );

    // Output
    printf("   Characters converted: %u\n", i);
    printf("    Multibyte character: %s\n\n",
     pMBBuffer );

    // Free multibyte character buffer
    if (pMBBuffer)
    {
    free(pMBBuffer);
    }
}

解决方法二

CString string2CString(string str)
{
	USES_CONVERSION;
	return A2T((LPSTR)(str.c_str()));
}

解决方法三

CString string2CString(string str)
{
	USES_CONVERSION;
	CString cstr;
	cstr.Format(_T("%s"),str.c_str());
	return cstr;
}

Reference

1. MSDN, Converts a sequence of wide characters to a corresponding sequence of multibyte characters
2. How to convert string to LPCTSTR?
3. How to convert std::string to LPCSTR?

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