Convert a 'System::String ^' to 'const char *' in vc++

6
votes

How can I convert a 'System::String ^' to 'const char *' in vc++?

My code:

String ^Result1= "C:/Users/Dev/Desktop/imag.jpg";

IplImage *img1 = cvLoadImage(Result1, 1);

if I do like above it will generate following error.

error C2664: 'cvLoadImage' : cannot convert parameter 1 from 'System::String ^' to 'const char *'

Please help me.

2
stringvisual-c++c++-clichar
possible duplicate of How do I convert a System::String^ to const char*? – shf301
possible duplicate of how to convert System::String to const char*? – Ben Voigt

2 Answers

12
votes

It's like this: How to convert from System::String* to Char* in Visual C++ 

System::String ^ str = "Hello world\n";

//method 1
pin_ptr<const wchar_t> str1 = PtrToStringChars(str);
wprintf(str1);  

//method 2
char* str2 = (char*)Marshal::StringToHGlobalAnsi(str).ToPointer();
printf(str2);
Marshal::FreeHGlobal((IntPtr)str2);

//method 3
CString str3(str); 
wprintf(str3);

//method 4
#if _MSC_VER > 1499 // Visual C++ 2008 only
marshal_context ^ context = gcnew marshal_context();
const char* str4 = context->marshal_as<const char*>(str);
puts(str4);
delete context;
#endif
3
votes

This is work for me. 

void MarshalString ( String ^ s, string& os ) {

   using namespace Runtime::InteropServices;

   const char* chars = 
      (const char*)(Marshal::StringToHGlobalAnsi(s)).ToPointer();

   os = chars;

   Marshal::FreeHGlobal(IntPtr((void*)chars));
}