Re: LPCTSTR and CString

"mido1971" <mido1971@discussions.microsoft.com> ha scritto nel messaggio
news:32D88001-5DA4-4CB4-A97A-BF26F7AE4B36@microsoft.com...


The above code is wrong.

In fact, CString 'str' instance is built on the stack (it is a local
automatic variable). So, when function GetString() terminates, this variable
'str' (which is local to function body) is *destroyed*.
So, its content (the string) is lost.

What is safe to do is to return a CString instance:

  CString GetString()
  {
      CString str = ...
      ....

      return str;
  }


The warning is clear: you say that your function as a C interface, but you
are using a C++ class (CString) in that interface, and so you are
introducing a C++ element (CString class) into a pure C interface, and that
is not possible.

If you really want a C interface, you should consider passing the buffer
from the caller (i.e. the caller allocates a string buffer, and the called
function fills it):

<code>

extern "C" AFX_EXT_API void WINAPI GetString( TCHAR * destBuffer, size_t
destSizeInBytes )
{
   // Check destination buffer
   ASSERT( destBuffer != NULL );
   ASSERT( destSizeInBytes != 0 );

   CString str;
   ....
   work with your str instance ...
   ...

   //
   // Return string to the caller,
   // copying the string into caller's buffer.
   //
   // Use a safe string function to avoid buffer overruns.
   //
   StringCbCopy(
    destBuffer, // destination buffer
    destSizeInBytes, // its size in bytes
    str // source string
   );

}

</code>

You can use the above code like this:

  // Get string into local buffer
  TCHAR theString[ 300 ];
  GetString( theString, sizeof(theString) );

HTH,
Giovanni