Crashing help!!! [RESOLVED]

[DrHippyHomer]

The below code causes my VB code to crash with the ' The memory could not be "read" ' error.

BSTR WINAPI FormatID(HWND hWnd, LPCSTR sLine)
{
char *tmp = new char[strlen(sLine)];
int n;

n = <to be calculated>;
strcpy(tmp, sLine);
return BSTR(tmp[n]);
}

What I am trying to do is get the n'th character from sLine.

Any ideas, thanks in advanced.

[jim mcnamara]

BSTR WINAPI FormatID(HWND hWnd, LPCSTR sLine) 
{ 
char *tmp = new char[strlen(sLine)]; <- local variable
int n; 

n = <to be calculated>; 
strcpy(tmp, sLine); 
return BSTR(tmp[n]);  <- you return a local variable
}

If you return a local volatile variable to the calling function, the memory the variable lived cannot be guaranteed to there.
Volatile means it goes away when the function returns.

Try:
Use a Global variable

Pass a pointer to the return value into the funtion

Use a static pointer in the function and malloc (one time only)
memory. You have to clean up on exit with atexit()

[DrHippyHomer]

My code looks like :

#include <windows.h>

char *rtn;

BOOL APIENTRY DllMain(HANDLE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved)
{
return TRUE;
}

BSTR WINAPI FormatID(HWND hWnd, LPCSTR sLine)
{
//char *tmp = new char[strlen(sLine)];
int n;

n =<to be calculated>;
strcpy(rtn, sLine);
return BSTR(rtn[n]);
}

Sorry jim mcnamara could you show me the rest of what you were saying.
Cheers.

[crptcblade]

What's wrong with passing in a buffer for the character you want to get back?

[CornedBee]

You're casting the UNICODE value of the n'th character to a pointer and return this. You have a huge memory leak. I think that's reason enough for failure...

BSTR WINAPI FormatID(HWND hWnd, LPCSTR sLine)
{
  // the tmp is completly unnecessary
  int n;

  n = <to be calculated>;
  LPWSTR str;
  int iNeed = MultiByteToWideChar(CP_ACP, 0, sLine+n, 1, NULL, 0);
  str = new WCHAR[iNeed];
  iNeed = MultiByteToWideChar(CP_ACP, 0, sLine+n, 1, str, iNeed);
  if(iNeed == 0)
  {
    // ERROR!
  }
  BSTR out = SysAllocString(str);
  delete[] str;
  return out;
}

This is the only correct way to return a BSTR to VB.

[DrHippyHomer]

Many Thanks CornedBee