Convert unsigned long long to wchar_t * and concatenate - c++

Question

There are tons of questions on this issue and I have been attempting the various solutions. There seems to be dozens of ways to do this however none of them are working. I am very new to C++ and VS, working for about a month, and I am trying to code an auto Excel program using VC++. I am stuck trying to concatenate a wchar_t * and an unsigned long long. I assume the first step is to "convert" the unsigned long long to wchar_t *. I apologize for throwing in the whole code but I think it may help with showing what I am aiming for and if there are any other weaknesses in the code.
wchar_t * ex(wchar_t * dest, unsigned long long num);
int main()
{
unsigned long long num = 10;
wchar_t *dest= L"A2:B";
wchar_t * Path=ex(dest, num);
VARIANT param;
param.vt = VT_BSTR;
// param.bstrVal = SysAllocString(L"A2:B10");
param.bstrVal = SysAllocString(Path);
getchar();
return 0;
}
wchar_t * ex(wchar_t * dest, unsigned long long num)
{
// Convert num to wchar_t *
wchar_t *rangeMax = (wchar_t *)num;
// I think this is used to eliminate extra space in other solutions
// but not here. It could be useful.
const int MAX_CHARS = 50;
size_t count = wcsnlen_s(dest, MAX_CHARS);
wprintf(L"The length of the string is %ld characters\n", count);
// Throw dest into buf
wchar_t buf[25] = { 0 };
int r = wcscpy_s(buf, 25, dest);
if (r != 0) {
wprintf(L"wcscpy_s() failed %ld", r);
}
r = wcscat_s(buf, 25, rangeMax);
if (r != 0) {
wprintf(L"wcscat_s() failed %ld", r);
}
wprintf_s(buf);
return buf;
}
ex is an edited example from zetcode. I think it is close to being the solution, however when combining buf and rangeMax the code throws all sorts of memory exceptions and fails.
As you can see the final destination for the concatenated wchar_t * is as a BSTR in a VARIANT through SysAllocString.
I appreciate any suggestions on code improvement as well as how to make the code actually run!

Answer 1

As suggested using wstring functioned as intended. Thank you for pointing out I was returning a pointer to a local variable! Once back in main the type was changed to wchar_t * which passed nicely to SysAllocString() for use with my main program.
std::wstring ex(wchar_t * dest, unsigned long long num);
int main()
{
unsigned long long num = 10;
wchar_t *dest= L"A2:B";
std::wstring PathString= ex(dest, num);
wchar_t *wPath = (WCHAR *)PathString.c_str();
std::wcout << L"In main\n";
std::wcout << wPath << L'\n';
VARIANT param;
param.vt = VT_BSTR;
//param.bstrVal = SysAllocString(L"A2:B10");
param.bstrVal = SysAllocString(wPath);
getchar();
return 0;
}
std::wstring ex(wchar_t * dest, unsigned long long num)
{
std::wstring rangeMax = std::to_wstring(num);
std::wstring string(dest);
string += rangeMax;
std::wcout << L"In function\n";
std::wcout<<string<<L'\n';
return string;
}