Can gdb print a specific variable every time it breaks?

Question

I need to check a variable to find out if it is set correctly, which might be happening after several loops.

What I am doing now is something like follows:

(gdb) b myfile.cpp:180
(gdb) c
(gdb) p decoder.m_msg
(gdb) c
(gdb) p decoder.m_msg
(gdb) c
...

Can I have this variable decoder.m_msg automatically printed every time the program breaks?

score 42 · Answer 1 · answered Mar 21 '13 at 11:56

42

Use the display command:

(gdb> display decoder.m_msg

This will cause decoder.m_msg to be printed every time that the prompt is shown (not only after a breakpoint).

answered Mar 21 '13 at 11:56

Nathan Fellman

score 26 · Accepted Answer · edited Feb 28 '17 at 14:13

26

$ break myfile.cpp:180
Breakpoint 1 at 0x46ba0e: file myfile.cpp, line 180.

$ commands 1
> print decoder.m_msg
> end
$

edited Feb 28 '17 at 14:13

Mohamed Moanis

answered Mar 21 '13 at 11:59

Nice! I wasn't familiar with this! `display` may not always work because a variable may be out of scope, but a command list solves that. – Nathan Fellman Mar 21 '13 at 12:02

2 Answers2