struct device is a core data structure and therefore shouldn't use QString.
QString stores as UTF-16 (which is a very questionable choice in itself).
However, the real problem is that this puts us in lifetime-management
hell when interfacing with C code: The UTF-16 has to be converted to
UTF-8, but when returning such a string, this puts burden on the caller
who has to free it. In fact, instead of looping over devices from C-code
we had a callback that sent down temporary C-strings with qPrintable.
In contrast, std::string is guaranteed to store its data as
contiguous null-terminated and C-compatible strings. Therefore,
replace the QString by std::string. Keep the QString just in
one place that formats a hexadecimal number to avoid any
potential change.
The disadvantage of using std::string is that it will crash
when constructed with a NULL argument, consistent with C-style
functions such as strcmp, etc. Arguably, NULL is different
from the empty string even though we treat both as the same.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
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