Asisgn LPCWSTR array from std::wstring - c++

Question

I am creating a dynamic array of LPCWSTR, and want to assign values at run time.
I have following code :
cin>>count
LPCWSTR * lpwcstrArray = new LPCWSTR[count]();
for (int i = 0; i < count; i++)
{
// some logic to create different wstring on each iteration
wstring tempWString = L"somerandomstuff";
lpwcstrArray[i] = reinterpret_cast<LPSWSTR>tempWString.c_str();
}
Now if i access lpwcstrArray - all the indexs point at data of last string that was assigned.
I know this is not correct way to assign values, but i do not know the correct way.

Answer 1

wstring tempWString is created and destroyed with each iteration of the loop.
You have dangling pointers in your lpwcstrArray and are experiencing undefined behaviour when you access one of them.
You need to allocate the space yourself or use a std::wstring as the array type instead of a LPCWSTR.

Answer 2

You are storing pointers that point at the internals of temporary std::wstring objects. When those objects are destroyed on each loop iteration, your array is left with danging pointers. You need to dynamically allocate the individual strings instead, eg:
std::cin >> count
LPWSTR *lpwstrArray = new LPWSTR[count];
for (int i = 0; i < count; i++)
{
// some logic to create different wstring on each iteration
std::wstring tempWString = L"somerandomstuff";
LPWSTR str = new WCHAR[tempWString.length()+1];
const wchar_t *p = tempWString.c_str();
std::copy(p, p+tempWString.length(), str);
lpwstrArray[i] = str;
}
// use lpwstrArray as needed...
// don't forget to free the memory when you are done using it...
for (int i = 0; i < count; i++)
delete[] lpwstrArray[i];
delete[] lpwstrArray;
Depending on what you are really trying to accomplish, something more like the following would be safer, at least if you just need read-only access to the strings (which you likely do, as the C in LPCWSTR stands for const, so the user of the array is not going to be modifying them):
std::cin >> count
std::vector<std::wstring> wstrArray(count);
for (int i = 0; i < count; i++)
{
// some logic to create different wstring on each iteration
wstrArray[i] = L"somerandomstuff";
}
std::vector<LPWSTR> lpwstrArray(count);
for (int i = 0; i < count; i++)
lpwstrArray[i] = const_cast<wchar_t*>(wstrArray[i].c_str());
// use lpwstrArray as needed. if you need to pass it where an
// LPWSTR* is expected, you can use &lpwstrArray[0] for that...
// lpwstrArray and wstrArray will be freed automatically
// when they go out of scope...

Answer 3

Try the approach
std::wstring ws(_T("Hello"));
LPCTSTR lps= (LPCTSTR)(ws.c_str());
TRACE(lps);
Notes:
You should not use the W types directly (ex: LPCWSTR). Use the T types instead (ex: LPCTSTR). Why? Because they will automatically translate to the version they should be (LPCSTR for non-Unicode / ASCII; LPCWSTR for Unicode), depending on your project.
For the same reason you should surround your strings with _T() or precede them with an L.
Try to dive deep using "Go To Definition" successively beginning on LPCTSTR
See also the _tcscpy_s function documentation