Avoid allocating memory using strdup() and then releasing it using
operator delete. strdup()-allocated memory should be released using
free(), not delete. But in these specific cases, there really was
never any good reason to duplicate the C-style strings in the first
place. Instead, we can safely pass those NUL-terminated char pointers
directly in calls to JNI's NewStringUTF(). NewStringUTF() does not
take ownership of its argument, but rather clones that string data
internally before returning. So using strdup() and delete was just
unnecessary memory churn.
In cases where we need to format, concatenate, or construct new
strings, don't use sprintf() into variable-sized, stack-allocated
arrays. Variable-sized arrays are not portable, and in particular are
rejected by Microsoft's Visual Studio 2017 C++ compiler. Instead, do
our string formatting and manipulations using std::ostringstream
and/or std::string. We just need to be a bit careful about the
lifetimes and ownership responsibilities of allocated data. In
brief, (1) ostringstream::str() returns a temporary string instance
that expires at the end of the enclosing statement, independent of the
lifetime of the ostringstream instance; while (2) string::c_str()
returns an pointer to internal data that remains valid as long as the
string on which it was called is valid and unmodified.
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