divelog: turn owning-pointers into unique_ptr<>s

Since everything is C++ now, we can use unique_ptr<>s. This makes
the code significantly shorter, because we can now use the default
move constructor and assignment operators.

This has a semantic change when std::move()-ing the divelog:
now not the contents of the tables are moved, but the pointers.
That is, the moved-from object now has no more tables and
must not be used anymore. This made it necessary to replace
std::move()s by std::swap()s. In that regard, the old code was
in principle broken: it used moved-from objects, which may work
but usually doesn't.

This commit adds a myriad of .get() function calls where the code
expects a C-style pointer. The plan is to remove virtually all of
them, when we move free-standing functions into the class it acts
on. Or, replace C-style pointers by references where we don't support
NULL.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/divelog.h

@@ -1,32 +1,33 @@
 // SPDX-License-Identifier: GPL-2.0
-// A structure that contains all the values we save in a divelog file
+// A structure that contains all the data we store in a divelog files
 #ifndef DIVELOG_H
 #define DIVELOG_H
 
+#include <memory>
+
 struct dive_table;
 struct trip_table;
 class dive_site_table;
 struct device_table;
 struct filter_preset_table;
 
-#include <stdbool.h>
-
 struct divelog {
-	struct dive_table *dives;
-	struct trip_table *trips;
-	dive_site_table *sites;
-	struct device_table *devices;
-	struct filter_preset_table *filter_presets;
+	std::unique_ptr<dive_table> dives;
+	std::unique_ptr<trip_table> trips;
+	std::unique_ptr<dive_site_table> sites;
+	std::unique_ptr<device_table> devices;
+	std::unique_ptr<filter_preset_table> filter_presets;
 	bool autogroup;
+
 	divelog();
 	~divelog();
-	divelog(divelog &&log); // move constructor (argument is consumed).
-	divelog &operator=(divelog &&log); // move assignment (argument is consumed).
+	divelog(divelog &&); // move constructor (argument is consumed).
+	divelog &operator=(divelog &&); // move assignment (argument is consumed).
+
 	void delete_single_dive(int idx);
 	void clear();
 };
 
 extern struct divelog divelog;
 
-
 #endif