C++: open file for writing in the LocalStorage

Hi guys, could you tell me how to open file for writing in the phone app LocalStorage for the non-unlocked handset (regular app for store)?
Code below doesn't work :(

Code:

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FILE *tmp;
auto tmpPath = Windows::Storage::ApplicationData::Current->LocalFolder->Path + "\tmp.txt";
auto tmpErr = _wfopen_s(&tmp, tmpPath->Data(), L"w");

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Any suggestions?