How to: Convert System::String to wchar_t* or char*

在.net平台上使用c++/clr开发，经常会遇到这样一个问题：How to: Convert System::String to wchar_t* or char* ？

MSDN上的这篇文章会打消你的疑虑，告诉你一个转换途径。（简单的英文，恕不翻译）

You can use PtrToStringChars in Vcclr.h to convert String to native wchar_t * or char *. This always returns a wide Unicode string pointer because CLR strings are internally Unicode. You can then convert from wide as shown in the following example.

Example

// convert_string_to_wchar.cpp
// compile with: /clr
#include < stdio.h >
#include < stdlib.h >
#include < vcclr.h >

using namespace System;

int main() {
   String ^str = "Hello";

   // Pin memory so GC can't move it while native function is called
   pin_ptr<const wchar_t> wch = PtrToStringChars(str);
   printf_s("%S ", wch);

   // Conversion to char* :
   // Can just convert wchar_t* to char* using one of the 
   // conversion functions such as: 
   // WideCharToMultiByte()
   // wcstombs_s()
   // ... etc
   size_t convertedChars = 0;
   size_t  sizeInBytes = ((str->Length + 1) * 2);
   errno_t err = 0;
   char    *ch = (char *)malloc(sizeInBytes);

   err = wcstombs_s(&convertedChars, 
                    ch, sizeInBytes,
                    wch, sizeInBytes);
   if (err != 0)
      printf_s("wcstombs_s  failed! ");

    printf_s("%s ", ch);
}

Output:

HelloHello