mbedit_prog.c: operation on ‘*(ping[i].beamflag + (sizetype)j)’ may be undefined [-Wsequence-point]

[schwehr]

With

gcc (Debian 8.3.0-6) 8.3.0

I see:

gcc -DHAVE_CONFIG_H -I. -I../../src/mbio  -I../../src/mbio -I../../src/mbaux -I../../src/gsf  -I/usr/include    -g -O2 -Wno-format -Wno-stringop-truncation -Wno-stringop-overflow -Wall -Wextra -Wno-sign-compare -Wno-maybe-uninitialized -Wno-format-overflow -MT mbedit_prog.o -MD -MP -MF $depbase.Tpo -c -o mbedit_prog.o mbedit_prog.c &&\
mv -f $depbase.Tpo $depbase.Po
mbedit_prog.c: In function ‘mbedit_action_mouse_restore’:
mbedit_prog.c:1847:28: warning: operation on ‘*(ping[i].beamflag + (sizetype)j)’ may be undefined [-Wsequence-point]
        ping[i].beamflag[j] = ping[i].beamflag[j] = mb_beam_set_flag_none(ping[i].beamflag[j]);
mbedit_prog.c: In function ‘mbedit_filter_ping’:
mbedit_prog.c:3343:32: warning: operation on ‘*(ping[iping].beamflag + (sizetype)j)’ may be undefined [-Wsequence-point]
        ping[iping].beamflag[j] = ping[iping].beamflag[j] = mb_beam_set_flag_filter2(ping[iping].beamflag[j]);
mbedit_prog.c:3364:32: warning: operation on ‘*(ping[iping].beamflag + (sizetype)j)’ may be undefined [-Wsequence-point]
        ping[iping].beamflag[j] = ping[iping].beamflag[j] = mb_beam_set_flag_filter2(ping[iping].beamflag[j]);
mbedit_prog.c:3391:33: warning: operation on ‘*(ping[iping].beamflag + (sizetype)j)’ may be undefined [-Wsequence-point]
         ping[iping].beamflag[j] = ping[iping].beamflag[j] =
mbedit_prog.c:3415:33: warning: operation on ‘*(ping[iping].beamflag + (sizetype)j)’ may be undefined [-Wsequence-point]
         ping[iping].beamflag[j] = ping[iping].beamflag[j] =

e.g. What is this supposed to be? It looks like a = a = mb_beam_set_flag_none(a)

if (!mb_beam_ok(ping[i].beamflag[j]) && !mb_beam_check_flag_unusable(ping[i].beamflag[j]))
    ping[i].beamflag[j] = ping[i].beamflag[j] = mb_beam_set_flag_none(ping[i].beamflag[j]);

[dwcaress]

Agreed - it should just be:
ping[i].beamflag[j] = mb_beam_set_flag_none(ping[i].beamflag[j]);