c++ - Passing a string from a DLL to C# -

i have c# application accesses functions unmanaged c++ libary using cli dll. problem can't text c++ library passed through c# application correctly. code have far follows:

c#

[dllimport("wrapper.dll", entrypoint = "getnamelength", callingconvention = callingconvention = callingconvention.cdecl)] public static extern bool _getnamelength( int index, out int size); [dllimport("wrapper.dll", charset = charset.ansi, entrypoint = "getname", callingconvention = callingconvention.cdecl)] public static extern bool _getname( out stringbuilder name, int size, int index);  private void testfunction() {     int size = 0;     _getnamelength(2, out size);     stringbuilder str = new stringbuilder(size + 1);      _getname(out str, str.capacity, 2);      btnname.text = str.tostring(); } 

cli

// in header. #define dllexport __declspec( dllexport)  extern "c" {     dllexport bool __cdecl getnamelength( int index, int& size);     dllexport bool __cdecl getname( char* name, int size, int index); };   // in '.cpp'. bool __cdecl getnamelength( int index, int& size) {     if( gp_app == nullptr)         return false;      gp_app->getnamelength( index, size);      return true; }  bool __cdecl getname( char* name, int index, int size) {     if( gp_app == nullptr)         return false;      const char* n = "";     n = gp_app->getname( index);      name = new char[size];     strcpy( name, n);      return true; } 

c++

// in header. class app {     void getnamelength( int index, int& size);     const char* getname( int index); };  // in '.cpp'. void app::getnamelength( int index, int& size) {     if( index >= 0 && index < gs_namescount)         size = strlen( gs_names[index]); }  const char* app::getname( int index) {     if( index >= 0 && index < gs_namescount)         return gs_names[index];      return nullptr; } 

i able debug dll , i've seen copy name on correctly, when use name = const_cast<char*>( n) (and when use string instead of stringbuilder), reason value isn't getting c# dll.

i read possible reason because c++ may use ascii characters while c# uses 16-bit characters, , fix include charset = charset.ansi it's marshalled correctly when it's returned c#, apparently hasn't helped.

can tell me i'm doing wrong?

solution:
use public ref class instead of namespace , declare functions using void foo( [out] string^ %name) ensuring using namespace system::runtime::interopservices; included.

this tells me have managed c++ dll.

if( gp_app == nullptr)     return false; 

if can export managed class , use string parameter method.

check this: http://msdn.microsoft.com/library/windows/apps/hh699870.aspx