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  4. std::string to const WCHAR*

std::string to const WCHAR*

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  • J James R Twine

    MultiByteToWideChar(...) is the de-facto way to convert from ANSI to Unicode (Wide) strings, so you can look into that.    For something a little more Q&D, look into the (ATL) Conversion Macros like A2WC(...), T2WC(...), etc.  Note that on VC++ 6.0, these macros use the _alloc(...) function (if a conversion is required) so you have to be careful using them directly in loops.    Peace!

    -=- James


    If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
    Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
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    Stick
    wrote on last edited by
    #8

    Don't think I can use ATL and not sure how I would do that anyway yet. I'm programming a win32 dll.

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    • Z Zac Howland

      Use a wstring and call the c_str() method on it.

      If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week Zac

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      Stick
      wrote on last edited by
      #9

      Would if I could, but I am given a c_str and must convert it to a wide, hence the question.

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      • D David Crow

        The c_str() method is a member of both string and wstring. Is that what you are asking?


        "Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

        "Judge not by the eye but by the heart." - Native American Proverb

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        James R Twine
        wrote on last edited by
        #10

        No, I am verifying that even though he is using std::string (ANSI) instead of std::wstring (Unicode/Wide), he can still expect to get a const WCHAR* returned by std::string::c_str()?  I am under the impression that he will get a const **char*** from std::string::c_str(), and a const **WCHAR*** (or const wchar_t*) from std::**w**string::c_str().    Peace!

        -=- James


        If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
        Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
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        • S Stick

          Don't think I can use ATL and not sure how I would do that anyway yet. I'm programming a win32 dll.

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          James R Twine
          wrote on last edited by
          #11

          You can use the conversion macros without adding "real" ATL support to your project.     Anyway, MultiByteToWideChar(...) is likely the way to go - look it up in MSDN for usage info.    Peace!

          -=- James


          If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
          Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
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          • J James R Twine

            No, I am verifying that even though he is using std::string (ANSI) instead of std::wstring (Unicode/Wide), he can still expect to get a const WCHAR* returned by std::string::c_str()?  I am under the impression that he will get a const **char*** from std::string::c_str(), and a const **WCHAR*** (or const wchar_t*) from std::**w**string::c_str().    Peace!

            -=- James


            If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
            Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
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            David Crow
            wrote on last edited by
            #12

            Because string.c_str() returns a char* is why I indicated it would need to be a minimum. A typecast would still need to be applied (to make it wide). I don't use the STL, but a better solution would be to use wstring instead.


            "Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

            "Judge not by the eye but by the heart." - Native American Proverb

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            • S Stick

              ummm seems that would do the reverse of what I want. I want to go to a wide string from a cstr.

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              David Crow
              wrote on last edited by
              #13

              As I do not use the STL, I did not want to commit to a definite solution. That's why I prefaced it with, "At a minimum." From there you could have just cast it to a WCHAR*. A better solution is to use a wstring instead.


              "Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

              "Judge not by the eye but by the heart." - Native American Proverb

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              • S Stick

                Would if I could, but I am given a c_str and must convert it to a wide, hence the question.

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                David Crow
                wrote on last edited by
                #14

                Stick^ wrote:

                Would if I could, but I am given a c_str and must convert it to a wide, hence the question.

                c_str() is a method of wstring. No conversion is necessary as it is already "wide." Now if you are unable to change std::string to std::wstring, that's a different problem.


                "Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

                "Judge not by the eye but by the heart." - Native American Proverb

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                • S Stick

                  Would if I could, but I am given a c_str and must convert it to a wide, hence the question.

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                  Zac Howland
                  wrote on last edited by
                  #15

                  You are given a const char* you mean? If that is the case, use MultiByteToWideChar to convert the const char* to an array of const wchar_t* and pass that to your draw function (NOTE: that will only work for UNICODE builds -- for a more generic approach, look at the A2T macro)

                  If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week Zac

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                  • Z Zac Howland

                    You are given a const char* you mean? If that is the case, use MultiByteToWideChar to convert the const char* to an array of const wchar_t* and pass that to your draw function (NOTE: that will only work for UNICODE builds -- for a more generic approach, look at the A2T macro)

                    If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week Zac

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                    Stick
                    wrote on last edited by
                    #16

                    No. I'm given a std::string... here's the declaration: string m_ac; Now, if I attempt: m_graphics->DrawString(m_ac, -1, &font, PointF(8,8), NULL, &grnbrush); I get: Error 1 error C2664: 'Gdiplus::Status Gdiplus::Graphics::DrawString(const WCHAR *,INT,const Gdiplus::Font *,const Gdiplus::RectF &,const Gdiplus::StringFormat *,const Gdiplus::Brush *)' : cannot convert parameter 1 from 'std::string' to 'const WCHAR *' so as you can clearly see, the m_ac is NOT already wide. I have tried to do something like this: WCHAR str[20+1] = L""; WideCharToMultiByte(CP_ACP, 0, m_ac.c_str(), -1, str, wcslen(str)+1, NULL, NULL); but this does not work either. Nor does just m_ac in parameter 3.

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                    • D David Crow

                      Because string.c_str() returns a char* is why I indicated it would need to be a minimum. A typecast would still need to be applied (to make it wide). I don't use the STL, but a better solution would be to use wstring instead.


                      "Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

                      "Judge not by the eye but by the heart." - Native American Proverb

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                      James R Twine
                      wrote on last edited by
                      #17

                      The const char* returned by c_str() is not a wide string, while casting it to WCHAR* will allow the code to compile, it will not work correctly.    Peace!

                      -=- James


                      If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
                      Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
                      DeleteFXPFiles & CheckFavorites (Please rate this post!)

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                      • J James R Twine

                        The const char* returned by c_str() is not a wide string, while casting it to WCHAR* will allow the code to compile, it will not work correctly.    Peace!

                        -=- James


                        If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
                        Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
                        DeleteFXPFiles & CheckFavorites (Please rate this post!)

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                        Jorgen Sigvardsson
                        wrote on last edited by
                        #18

                        James R. Twine wrote:

                        while casting it to WCHAR* will allow the code to compile, it will not work correctly.

                        From the context, I think he meant casting the entire string, and not the pointer. :)

                        -- Mr. Bender's Wardrobe by ROBOTANY 500

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                        • S Stick

                          No. I'm given a std::string... here's the declaration: string m_ac; Now, if I attempt: m_graphics->DrawString(m_ac, -1, &font, PointF(8,8), NULL, &grnbrush); I get: Error 1 error C2664: 'Gdiplus::Status Gdiplus::Graphics::DrawString(const WCHAR *,INT,const Gdiplus::Font *,const Gdiplus::RectF &,const Gdiplus::StringFormat *,const Gdiplus::Brush *)' : cannot convert parameter 1 from 'std::string' to 'const WCHAR *' so as you can clearly see, the m_ac is NOT already wide. I have tried to do something like this: WCHAR str[20+1] = L""; WideCharToMultiByte(CP_ACP, 0, m_ac.c_str(), -1, str, wcslen(str)+1, NULL, NULL); but this does not work either. Nor does just m_ac in parameter 3.

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                          George L Jackson
                          wrote on last edited by
                          #19

                          Have you tried "mbstowcs" or "mbstowcs_s" in stdlib.h. std::string mbstr = "The string!"; std::vector<wchar_t> wcstr(mbstr.size() + 1, L'\0'); size_t written = 0; mbstate_t state = {0}; const char* pmbstr = mbstr.c_str(); errno_t result = mbsrtowcs_s(&written, &wcstr[0], wcstr.size(), &pmbstr, mbstr.size(), &state); std::wcout << &wcstr[0] << std::endl; -- modified at 20:19 Thursday 28th September, 2006

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                          • J Jorgen Sigvardsson

                            James R. Twine wrote:

                            while casting it to WCHAR* will allow the code to compile, it will not work correctly.

                            From the context, I think he meant casting the entire string, and not the pointer. :)

                            -- Mr. Bender's Wardrobe by ROBOTANY 500

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                            James R Twine
                            wrote on last edited by
                            #20

                            You mean to create a temporary, as in wstring( sTheString.c_str() )?  I do not think that will work, either...  Unless I am missing the intent of your smiley, that is.    Peace!

                            -=- James


                            If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
                            Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
                            DeleteFXPFiles & CheckFavorites (Please rate this post!)

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                            • J James R Twine

                              You mean to create a temporary, as in wstring( sTheString.c_str() )?  I do not think that will work, either...  Unless I am missing the intent of your smiley, that is.    Peace!

                              -=- James


                              If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
                              Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
                              DeleteFXPFiles & CheckFavorites (Please rate this post!)

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                              Jorgen Sigvardsson
                              wrote on last edited by
                              #21

                              Naw, more likely using CA2CW or something along those lines. My bet's on that David's a bit too experienced to fall for the (wchar_t*)str.c_str() and similar newbie mistakes. :)

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                              • S Stick

                                Don't think I can use ATL and not sure how I would do that anyway yet. I'm programming a win32 dll.

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                                Jorgen Sigvardsson
                                wrote on last edited by
                                #22

                                If you are using a fairly new version of MFC (7, 8), you can use the conversion classes such as CA2W without any hassles. Just include atlconv.h in stdafx.h, and you're set.

                                -- Not a substitute for human interaction

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                                • S Stick

                                  No. I'm given a std::string... here's the declaration: string m_ac; Now, if I attempt: m_graphics->DrawString(m_ac, -1, &font, PointF(8,8), NULL, &grnbrush); I get: Error 1 error C2664: 'Gdiplus::Status Gdiplus::Graphics::DrawString(const WCHAR *,INT,const Gdiplus::Font *,const Gdiplus::RectF &,const Gdiplus::StringFormat *,const Gdiplus::Brush *)' : cannot convert parameter 1 from 'std::string' to 'const WCHAR *' so as you can clearly see, the m_ac is NOT already wide. I have tried to do something like this: WCHAR str[20+1] = L""; WideCharToMultiByte(CP_ACP, 0, m_ac.c_str(), -1, str, wcslen(str)+1, NULL, NULL); but this does not work either. Nor does just m_ac in parameter 3.

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                                  Jorgen Sigvardsson
                                  wrote on last edited by
                                  #23

                                  Stick^ wrote:

                                  WideCharToMultiByte(CP_ACP, 0, m_ac.c_str(), -1, str, wcslen(str)+1, NULL, NULL);

                                  Please use MultiByteToWideChar() instead. You are converting from char to wchar_t, right?

                                  wchar_t buf[20+1] = { 0 };
                                  MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, m_ac.c_str(), m_ac.size(), buf, 20);

                                  should do the trick.

                                  -- From the Makers of Futurama

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                                  • J James R Twine

                                    The const char* returned by c_str() is not a wide string, while casting it to WCHAR* will allow the code to compile, it will not work correctly.    Peace!

                                    -=- James


                                    If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
                                    Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
                                    DeleteFXPFiles & CheckFavorites (Please rate this post!)

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                                    David Crow
                                    wrote on last edited by
                                    #24

                                    James R. Twine wrote:

                                    The const char* returned by c_str() is not a wide string,...

                                    So what exactly does std::wstring::c_str() return?


                                    "Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

                                    "Judge not by the eye but by the heart." - Native American Proverb

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                                    • D David Crow

                                      James R. Twine wrote:

                                      The const char* returned by c_str() is not a wide string,...

                                      So what exactly does std::wstring::c_str() return?


                                      "Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

                                      "Judge not by the eye but by the heart." - Native American Proverb

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                                      James R Twine
                                      wrote on last edited by
                                      #25

                                      std::**w**string::c_str() returns a const WCHAR* (const wchar_t*), but not std::string:c_str(), which is what the OP was asking about.    I think that we (I?) are just getting confused about what "width" of string object is in use here.  The OP is dealing with having a std::string (ANSI) object and needs to get a (presumably valid) const WCHAR* (Unicode) out of it.    Since they cannot simply change the strings from std::string to std::wstring, they are stuck with ANSI string objects, and no amount of casting is going to create a valid wide string from the return of std::string:c_str().   They need to call a conversion function (either directly or indirectly) in order to translate the string correctly.    Peace!

                                      -=- James


                                      If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
                                      Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
                                      DeleteFXPFiles & CheckFavorites (Please rate this post!)

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                                      • J James R Twine

                                        std::**w**string::c_str() returns a const WCHAR* (const wchar_t*), but not std::string:c_str(), which is what the OP was asking about.    I think that we (I?) are just getting confused about what "width" of string object is in use here.  The OP is dealing with having a std::string (ANSI) object and needs to get a (presumably valid) const WCHAR* (Unicode) out of it.    Since they cannot simply change the strings from std::string to std::wstring, they are stuck with ANSI string objects, and no amount of casting is going to create a valid wide string from the return of std::string:c_str().   They need to call a conversion function (either directly or indirectly) in order to translate the string correctly.    Peace!

                                        -=- James


                                        If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
                                        Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
                                        DeleteFXPFiles & CheckFavorites (Please rate this post!)

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                                        David Crow
                                        wrote on last edited by
                                        #26

                                        James R. Twine wrote:

                                        std::wstring::c_str() returns a const WCHAR* (const wchar_t*)...

                                        Which is why I suggested it as a better solution here.

                                        James R. Twine wrote:

                                        ...no amount of casting is going to create a valid wide string from the return of std::string:c_str().

                                        Agreed. :-O Blunder on my part.


                                        "Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

                                        "Judge not by the eye but by the heart." - Native American Proverb

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                                        • S Stick

                                          No. I'm given a std::string... here's the declaration: string m_ac; Now, if I attempt: m_graphics->DrawString(m_ac, -1, &font, PointF(8,8), NULL, &grnbrush); I get: Error 1 error C2664: 'Gdiplus::Status Gdiplus::Graphics::DrawString(const WCHAR *,INT,const Gdiplus::Font *,const Gdiplus::RectF &,const Gdiplus::StringFormat *,const Gdiplus::Brush *)' : cannot convert parameter 1 from 'std::string' to 'const WCHAR *' so as you can clearly see, the m_ac is NOT already wide. I have tried to do something like this: WCHAR str[20+1] = L""; WideCharToMultiByte(CP_ACP, 0, m_ac.c_str(), -1, str, wcslen(str)+1, NULL, NULL); but this does not work either. Nor does just m_ac in parameter 3.

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                                          Zac Howland
                                          wrote on last edited by
                                          #27

                                          You are compiling with UNICODE defined, so DrawString is mapped to DrawStringW (which takes wide characters). Since you have a string (which are ANSI characters), you need to convert that string to a wstring (or simply to an array of wchar_t's). You'll need to muse MultiByteToWideChar for that (not WideCharToMultiByte).

                                          If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week Zac

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