MC++ & C++/CLI String: How to convert 'System::String' to 'char*'?

Q: How to convert 'System::String' to 'char*' in MC++?

A: There are several methods (notice that the examples are only meant to show how to convert from 'System::String' to 'char*'):
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• Using 'PtrToStringChars()'
  
  You can access the wrapped buffer of a 'System::String' using this function, that yields a' __gc' pointer to the first character of a 'System::String' object. If it's passed to a function that expects an unmanaged string ('wchar_t'), it must me pinned first.
  <br>
  
  • In VC++ 7.x:
    <br>
    
    Code:

    ---

    #include <vcclr.h> // required header for PtrToStringChars

size_t GetSize(System::String* str)
{
  const wchar_t __pin* unmngStr = PtrToStringChars(str);
  return wcslen(unmngStr);
}

size_t size = GetString(S"Method 1");

    ---

    <br>
  • In VC++ 8:
    <br>
    
    Code:

    ---

    #include <vcclr.h> // required header for PtrToStringChars

size_t GetSize(System::String^ str)
{
  pin_ptr<const wchar_t> unmngStr = PtrToStringChars(str);
  return wcslen(unmngStr);
}

size_t size = GetString("Method 1");

    ---

  
  <br><br>
• Using 'StringToHGlobalAnsi()'
  
  Method 'StringToHGlobalAnsi()' of the Marshal class from the .NET Framework copies the contents of a managed string into unmanaged memory, converting into ANSI format as it copies. Notice, that you'll have to call the 'FreeHGlobal()' method to release the allocated memory.
  <br>
  
  • In VC++ 7.x:
    <br>
    
    Code:

    ---

    using namespace System::Runtime::InteropServices; // for class Marshal

void PrintMessage(System::String* str)
{
        TCHAR* str2 = (TCHAR*)(void*)Marshal::StringToHGlobalAnsi(str);
        printf(str2);
        Marshal::FreeHGlobal(str2);
}

PrintMessage(S"Method 2");

    ---

    <br>
  • In VC++ 8:
    <br>
    
    Code:

    ---

    using namespace System::Runtime::InteropServices; // for class Marshal

void PrintMessage(System::String^ str)
{
        const char* str2 = (char*)(void*)Marshal::StringToHGlobalAnsi(str);
        printf(str2);
        Marshal::FreeHGlobal((System::IntPtr)(void*)str2);
}

PrintMessage("Method 2");

    ---

  
  <br><br>
• Using 'CString' class.
  <br>
  
  • In VC++ 7.x, class 'CString' has a special constructor that takes a 'System::String' object:
    <br>
    
    Code:

    ---

    #ifdef _MANAGED

        // This template will compile only for
        // class SystemString == System::String

        template<class SystemString>
        CStringT( SystemString * pString ) :
                CThisSimpleString( StringTraits::GetDefaultManager() )
        {
                const wchar_t __pin* psz = PtrToStringChars( pString );
                *this = psz;
        }
#endif

    ---

    Using this constructor you can write:
    <br>
    
    Code:

    ---

    #include <atlstr.h> // for class CString

void Print(System::String* str)
{
        CString cstr(str);
        printf(cstr);
}

Print(S"Method 3");

    ---

    <br>
  • In VC++ 8 (2005) the 'CString' constructor looks like this:
    <br>
    
    Code:

    ---

    #if defined(__cplusplus_cli)

        template <class SystemString>
        CStringT( SystemString^ pString ) :
                CThisSimpleString( StringTraits::GetDefaultManager() )
        {
                cli::pin_ptr<const System::Char> pChar = PtrToStringChars( pString);
                const wchar_t *psz = pChar;
                *this = psz;
        }

#elif defined(_MANAGED)

        template <class SystemString>
        CStringT( SystemString __gc* pString ) :
                CThisSimpleString( StringTraits::GetDefaultManager() )
        {               
                const wchar_t __pin* psz = PtrToStringChars( pString );
                *this = psz;
        }

#endif

    ---

    As a result, the previous example changes to:
    <br>
    
    Code:

    ---

    #include <atlstr.h> // for class CString

void Print(System::String^ str)
{
        CString cstr(str);
        wprintf(cstr);
}

Print("Method 3");

    ---

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