Show errors in my gdb log report - gdb

Question

Here is a sample session directly from gdb console
Starting program:
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Breakpoint 1, 0x00000000025654f0 in ~F()
(gdb) bt
#0 0x00000000025654f0 in ~F()
at hello.cpp:123
(gdb) c
Continuing.
foo.cpp:122:12: runtime error: member call on null pointer of type 'Object'
Here is my .gdbinit file
set pagination off
set language c++
set print pretty on
set logging file gdb.txt
set logging on
break ~F()
info breakpoints
r
bt
c
set logging off
quit
and the gdb.txt produced looks something like this:
Breakpoint 1 at 0x25654f0
Num Type Disp Enb Address What
1 breakpoint keep y 0x00000000025654f0 <~F()>
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Breakpoint 1, 0x00000000025654f0 in ~F()
#0 0x00000000025654f0 in ~F()
....
Breakpoint 1, 0x00000000025654f0 in ~F()
I don't see foo.cpp:122:12: runtime error: member call on null pointer of type 'Object' coming out in the log. How do I get that into my log?
Thanks

Answer 1

That message come from your program, not from gdb.
One way to make it work is to have your program and gdb write to the same log. The only trick here is to make sure they are both writing in "append" mode. There is a "set logging" subcommand for this, and for your program, you can run like:
(gdb) run >> log