Opc Client 写入String 问题

 bool WriteOPCCItem(..., std::string strval,...)

{    ........
      VARIANT variant；

      variant.vt = VT_BST;

      wchar_t *pwchar;

      pwchar = WSTRFromString(strval.c_str());

      variant.bstrVal = SysAllocString(pwchar);  

      WSTRFree（pwchar ）;

      ........//写入值

}

wchar_t* WSTRFromString(const char *buf)
{
    intlength, i;
    wchar_t*temp;
    length = strlen(buf) + 1;
    temp = new wchar_t[strlen(buf) + 1];
    if(temp)
    {
        for(i=0; i<length; i++) temp[i] = (wchar_t) buf[i];
    }
    return temp;
}
void  WSTRFree(wchar_t *c)
{
    if (c == NULL)
        return;
    delete c;
}