Pose backup: convert from C to C++

Convert `pose_backup.c` (in C) to `pose_backup.cc` (in C++). This will
make future improvements easier. For now, it's the same code with just
some additional explicit casts (C++ doesn't allow implicitly casting
`void *`), `NULL` changed into `nullptr`, and some other simple changes.

No functional changes.

source/blender/editors/armature/CMakeLists.txt

@@ -44,7 +44,7 @@ set(SRC
   armature_utils.c
   editarmature_undo.c
   meshlaplacian.c
-  pose_backup.c
+  pose_backup.cc
   pose_edit.c
   pose_group.c
   pose_lib.c

source/blender/editors/armature/pose_backup.cc

@@ -20,7 +20,7 @@
 
 #include "ED_armature.h"
 
-#include <string.h>
+#include <cstring>
 
 #include "BLI_listbase.h"
 
@@ -44,23 +44,23 @@ typedef struct PoseChannelBackup {
   struct IDProperty *oldprops; /* Backup copy (needs freeing) of pose channel's ID properties. */
 } PoseChannelBackup;
 
-typedef struct PoseBackup {
+struct PoseBackup {
   bool is_bone_selection_relevant;
   ListBase /* PoseChannelBackup* */ backups;
-} PoseBackup;
+};
 
 static PoseBackup *pose_backup_create(const Object *ob,
                                       const bAction *action,
                                       const bool is_bone_selection_relevant)
 {
-  ListBase backups = {NULL, NULL};
-  const bArmature *armature = ob->data;
+  ListBase backups = {nullptr, nullptr};
+  const bArmature *armature = static_cast<const bArmature *>(ob->data);
 
   /* TODO(Sybren): reuse same approach as in `armature_pose.cc` in this function, as that doesn't
    * have the assumption that action group names are bone names. */
   LISTBASE_FOREACH (bActionGroup *, agrp, &action->groups) {
     bPoseChannel *pchan = BKE_pose_channel_find_name(ob->pose, agrp->name);
-    if (pchan == NULL) {
+    if (pchan == nullptr) {
       continue;
     }
 
@@ -68,7 +68,8 @@ static PoseBackup *pose_backup_create(const Object *ob,
       continue;
     }
 
-    PoseChannelBackup *chan_bak = MEM_callocN(sizeof(*chan_bak), "PoseChannelBackup");
+    PoseChannelBackup *chan_bak = static_cast<PoseChannelBackup *>(
+        MEM_callocN(sizeof(*chan_bak), "PoseChannelBackup"));
     chan_bak->pchan = pchan;
     memcpy(&chan_bak->olddata, chan_bak->pchan, sizeof(chan_bak->olddata));
 
@@ -80,7 +81,7 @@ static PoseBackup *pose_backup_create(const Object *ob,
   }
 
   /* PoseBackup is constructed late, so that the above loop can use stack variables. */
-  PoseBackup *pose_backup = MEM_callocN(sizeof(*pose_backup), __func__);
+  PoseBackup *pose_backup = static_cast<PoseBackup *>(MEM_callocN(sizeof(*pose_backup), __func__));
   pose_backup->is_bone_selection_relevant = is_bone_selection_relevant;
   pose_backup->backups = backups;
   return pose_backup;
@@ -96,7 +97,7 @@ PoseBackup *ED_pose_backup_create_selected_bones(const Object *ob, const bAction
   /* See if bone selection is relevant. */
   bool all_bones_selected = true;
   bool no_bones_selected = true;
-  const bArmature *armature = ob->data;
+  const bArmature *armature = static_cast<const bArmature *>(ob->data);
   LISTBASE_FOREACH (bPoseChannel *, pchan, &ob->pose->chanbase) {
     const bool is_selected = PBONE_SELECTED(armature, pchan->bone);
     all_bones_selected &= is_selected;