Problem with reading PNG metadata due to unicode strings

Question

Being new to the XMP SDK I have problems trying to dump the XMP data from a .png file because the data contains UTF-8 data.
I have searched the forum for answers, but the answers I found do not help.
The answer I found was to replace std::string with std::wstring. but that causes problems with the compile - btw, I am using MSVC 2010 C++ Express
and XMP SDK-CC201306
Changing the std:: line to:
#define TXMP_STRING_TYPE std::wstring
and all string definitions in my code to wstring, gives me a bunch of compile errors, such as:
f:\pkg\c++\xmp-toolkit-sdk-cc201306\public\include\client-glue/TXMPMeta.incl_cpp(74): error C2664: 'std::basic_string<_Elem,_Traits,_Ax> &std::basic_string<_Elem,_Traits,_Ax>::assign(const _Elem *,unsigned int)' : cannot convert parameter 1 from 'XMP_StringPtr' to 'const wchar_t *'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>,
1>              _Ax=std::allocator<wchar_t>
1>          ]
1>          Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
1>          f:\pkg\c++\xmp-toolkit-sdk-cc201306\public\include\client-glue/TXMPMeta.incl_cpp(72) : while compiling class template member function 'void TXMPMeta<tStringObj>::SetClientString(void *,XMP_StringPtr,XMP_StringLen)'
1>          with
1>          [
1>              tStringObj=std::wstring
1>          ]
1>          f:\pkg\c++\XMP-Toolkit-SDK-cc201306\public\include\XMP.incl_cpp(55) : see reference to class template instantiation 'TXMPMeta<tStringObj>' being compiled
1>          with
1>          [
1>              tStringObj=std::wstring
1>          ]
Any help or pointers will be most welcome.
TIA,
DayWalker

Answer 1

OK, I now understand the point you were driving at.
To check out this idea, I have modified the code in the routine which dumps the output from the callback to a file as follows:
(Though if you were to dump the file using the std:: stream - .i.e. using the utility as supplied, you should see the same problem - it is not at all dependent on my using the wxWidgets toolkit)
XMP_Status DumpXMPToFile(void * WXUNUSED(refCon), XMP_StringPtr buffer, XMP_StringLen bufferSize )
    XMP_Status status = 0;
    wxString wsT;
    try
    wxString wsText( buffer, wxConvUTF8 );
    if( g_wfDumpFile.IsOpened() )
      wsT.Printf( _T("<%s> size(%d)"), wsText, bufferSize );
      g_wfDumpFile.SeekEnd();
      g_wfDumpFile.Write( wsT, wsT.Length() );
    else
      return -1;
    catch(XMP_Error & e)
The output for the one line in question:
<Iptc4xmpCore:CiAdrExtadr> size(24)< = "> size(4)<Leo-Saurer-Straße> size(15)<> size(1)<C3> size(2)<> size(1)<9F> size(2)<>> size(1)<e> size(1)<"> size(1)<
> size(1)<   > size(3)<   > size(3)<   > size(3)
The hex contents of the buffer I get in the callback is
0x003908D0  4c 65 6f 2d 53 61 75 72 65 72 2d 53 74 72 61 c3 9f 65 00 cd cd cd cd  Leo-Saurer-Straße.ÍÍÍÍ
0x003908E7  cd cd cd cd cd cd cd cd cd fd fd fd fd ab ab ab ab ab ab ab ab ee fe  ÍÍÍÍÍÍÍÍÍýýýý««««««««îþ
As you can see, my conversion routines takes all the buffer contains and converts it to the appropriate UTF-8 string, even though the count passed to me is short and represents only the count up to the first non-ASCII character and all of the subsequent strings  - interpreted as hex values by the caller of the call back would not give me the correct characters, athough they are passed to me for display.
The two fragments of one byte length are the ones I could not find in the actual output.
The call stack at that point:
>
wxMeta.exe!DumpXMPToFile(void * __formal, const char * buffer, unsigned long bufferSize)  Line 110
C++
wxMeta.exe!TextOutputProcWrapper(void * refCon, const char * buffer, unsigned long bufferSize)  Line 60 + 0x18 bytes
C++
wxMeta.exe!DumpClearString(const std::basic_string<char,std::char_traits<char>,std::allocator<char> > & value, long (void *, const char *, unsigned long)* outProc, void * refCon)  Line 409 + 0x1c bytes
C++
wxMeta.exe!DumpPropertyTree(const XMP_Node * currNode, int indent, unsigned int itemIndex, long (void *, const char *, unsigned long)* outProc, void * refCon)  Line 161 + 0x14 bytes
C++
wxMeta.exe!DumpPropertyTree(const XMP_Node * currNode, int indent, unsigned int itemIndex, long (void *, const char *, unsigned long)* outProc, void * refCon)  Line 222 + 0x1f bytes
C++
wxMeta.exe!XMPMeta::DumpObject(long (void *, const char *, unsigned long)* outProc, void * refCon)  Line 1100 + 0x23 bytes
C++
wxMeta.exe!WXMPMeta_DumpObject_1(__XMPMeta__ * xmpObjRef, long (void *, const char *, unsigned long)* outProc, void * refCon, WXMP_Result * wResult)  Line 968
C++
wxMeta.exe!TXMPMeta<std::basic_string<char,std::char_traits<char>,std::allocator<char> > >::DumpObject(long (void *, const char *, unsigned long)* outProc, void * refCon)  Line 833 + 0x21 bytes
C++
wxMeta.exe!MyFrame::DisplayMetaData(wxString & wsrFilePathAndName)  Line 484
C++
Hoping this will help resolve the issue :-)