swprintf_s [https://msdn.microsoft.com/en-us/library/ce3zzk1k.aspx ]
const wchar_t *format,
Maximum number of characters to store.
Documentation says the argument is the number of characters to store and not the size of buffer. More often, such APIs asks for the size of buffer and even in this case would work fine if it were not wide character string where each character takes two bytes, vs. 1 byte in normal string.
swprintf_s ( buff, sizeof(buff), L”string to %s “, “format” );
this will end up corrupting stack variables. You may crash for various reasons, all manifestations of this corruption. The right way would be to read the documentations
swprintf_s (buff, sizeof(buff)/sizeof(wchar_t), L”string to %s”, L”format”);
Hope this help!