const WCHAR * myVar vs const char * myVar

Question

I've developed a small bmp to jpg conveter. Following code is working and providing exact results as I need

BOOLEAN convertBMPtoJPG(const WCHAR *src_bmp_path,const WCHAR *dest_jpeg_path);

then calling function as,

const WCHAR *src_bmp_path = L"test.bmp";
const WCHAR *dest_jpeg_path= L"test.jpg";
convertBMPtoJPG(src_bmp_path,dest_jpeg_path);

However I need the function to be changed as following (as per requirements I've been given), but doing so results as a compilation error.

BOOLEAN convertBMPtoJPG(char *src_bmp_path,char *dest_jpeg_path);

then function would be called as, (though I need to follow just the prototype as above),

char *src_bmp_path = "test.bmp";
char *dest_jpeg_path= "test.jpg";
convertBMPtoJPG(src_bmp_path,dest_jpeg_path);

Another question on stackover provided too much information about Win32 types, however I yet couldn't resolve the issue. I'm not that great in Win32 API, please guide me what's going wrong in later approach.

Edit:

Error Message: error C2664: 'Gdiplus::Status Gdiplus::Image::Save(const WCHAR *,const CLSID *,const Gdiplus::EncoderParameters *)' : cannot convert parameter 1 from 'char *' to 'const WCHAR *' 1> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

Answer 1

Image::Save() only accepts WCHAR* values, so your char* wrapper will have to convert to WCHAR* , such as with MultiByteToWideChar() (just like Win32 API Ansi functions do when they call Win32 API Unicode functions internally), eg:

std::wstring towstring(const char *src)
{
    std::wstring output;
    int src_len = strlen(src);
    if (src_len > 0)
    {
        int out_len = MultiByteToWideChar(CP_ACP, 0, src, src_len, NULL, 0);
        if (out_len > 0)
        {
            output.resize(out_len);
            MultiByteToWideChar(CP_ACP, 0, src, src_len, &output[0], out_len);
        }
    }
    return output;
}

BOOLEAN convertBMPtoJPG(char *src_bmp_path,char *dest_jpeg_path)
{
    return convertBMPtoJPG(towstring(src_bmp_path).c_str(), towstring(dest_jpeg_path).c_str());
}

BOOLEAN convertBMPtoJPG(const WCHAR *src_bmp_path, const WCHAR *dest_jpeg_path)
{
   // your existing conversion logic here...
}

Answer 2

Well, looks like your are compiling for Unicode support. The list of Win32 data types can be found here

WCHAR is defined as -

 A 16-bit Unicode character. For more information, see Character Sets Used By Fonts.
 This type is declared in WinNT.h as follows:
 typedef wchar_t WCHAR;

Here is a link showing how to convert between various string types String Conversion Samples.