Debug argument based C program with gdb

Question

I have c++ program which I run by passing string with it.

g++ -o a main.cpp -lpthread

and execute it with ./a "Good nice"

But how I debug it with gdb? main.cpp calling functions from other files which are included in it.

gdb ./a "Good nice"

takes "--" as files and says no such file!

I want to debug line by line!

possible duplicate of [Passing arguments to program run through gdb](http://stackoverflow.com/questions/4521015/passing-arguments-to-program-run-through-gdb) — mmmmmm, Aug 17 '13 at 07:49
Also compile your program with `-g` otherwise this is all for nothing — aaronman, Aug 17 '13 at 07:54

score 6 · Answer 1 · edited Aug 17 '13 at 11:04

6

Use the --args option of gdb:

gdb --args ./a "Good nice"

Also add the -g option to your compiler call, because otherwise gdb won't be able to connect your executable with your source code:

g++ -g -o a main.cpp -lpthread

edited Aug 17 '13 at 11:04

Macmade

answered Aug 17 '13 at 07:49

he also has to compile with `-g` – aaronman Aug 17 '13 at 07:49
@aaronman yes, to be able to use the debugger at all. But wasn't this question about the program arguments problem? – cmaster - reinstate monica Aug 17 '13 at 07:50
If he shows you how he's compiling it and you know it's wrong and you don't tell him, is your answer useful? – aaronman Aug 17 '13 at 07:51
2

If we are at it, you should also add -Wall... ;-) – László Papp Aug 17 '13 at 09:03
@LaszloPapp Cheers :D but I think that would really start going off topic. I can upvote your comment, though. – cmaster - reinstate monica Aug 17 '13 at 09:10
first `g++ -g -o b main.cpp foo.cpp` then `gdb --args ./b "good nice" `. Then `s` for line by line execution gives `the program is not being run` – user123 Aug 17 '13 at 09:56
Well, in any case you need to say `run` to gdb before trying to step through a program. Before that, gdb does not start a process which you could debug. I know, it is awkward that gdb doesn't do this automatically when it starts, but that's the way it is. Likely, you'll want to set a breakpoint (`break`) after saying `run`, so that you don't have to step through your entire program to reach the interesting point, but that is optional, `run` breaks at the start of `main()`. Correct sequence: `g++ -g ...`, `gdb --args ...`, `run`, [`break ...`], all the other commands you use to debug your code. – cmaster - reinstate monica Aug 17 '13 at 12:50

Yu Hao · Answer 2 · 2013-08-17T07:59:46.440

5

Use gdb without argument

gdb ./a

Then in gdb, before running the program

set args "Good nice"

And you can see what arguments you set, use

show args

See here for detail.

edited Aug 17 '13 at 07:59

answered Aug 17 '13 at 07:49

Yu Hao

A side note: If in case you have doubts in middle what args you set, use `show args` – RajSanpui Aug 17 '13 at 07:57
@kingsmasher1 Exactly, I'm adding that to the answer. – Yu Hao Aug 17 '13 at 08:00
after above procedure when I press `s` to start line by line debug it gives ` the program is not being run ` – user123 Aug 17 '13 at 09:58
you need to run it by typing 'run'. – Yu Hao Aug 17 '13 at 10:17

elmov · Answer 3 · 2013-08-17T07:54:55.037

3

gdb ./prog -> set args string -> run.

edited Aug 17 '13 at 07:54

answered Aug 17 '13 at 07:49

elmov

This will execute entire program and gives output. I want line by line debug! – user123 Aug 17 '13 at 10:01

billz · Answer 4 · 2013-08-17T08:11:39.550

3

Anther choice is provide argument after run

$gdb ./a
 run "Good nice"

edited Aug 17 '13 at 08:11

answered Aug 17 '13 at 07:51

billz

4 Answers4