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Debugging using gdb or dbx

I need help using either dbx, gdb, or xxgdb. Please be specific.

Here is what I have already did and I was so confused.

1. I have put -g flag when compiled my C++ source
2. % dbx executable_file
3. I typed 'next' and got error message like this
    dbx: can't continue execution -- no active process

4. I tried to put a break point at line 8 using
    'stop at 8' command and I got another message:
   dbx: No current source file
5. Well, I scratched my head and typed 'quit'

Same story happened when I tried using both gdb and xxgdb.

Please help! I need to know how you debug your C++ codes in Unix, STEP by STEP!


PS: I use all my points and hope that I would get a very brilliant answer :)
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1 Solution
You can't step until you start running.

Try this:

gdb a.out

this will list out your program...

(gdb)break 12

Set a breakpoint at one of the lines in your program.  I've used 12 as an example, yours will vary.


Now when it hits the breakpoint, it will stop.  You can now:

v5Author Commented:
My output file is not a.out, I use -o a a.o. So, the executeable file is "a", not "a.out".

I try % gdb a

then (gdb)l

and I got an error msg
dbx: No current source file

I don't understand "-o a a.o".  When you compile with gcc the command should be:

gcc sourcefile.c -g -o a

This will give an executable "a" that contains debugging information.  Now you can say:

gdb a

If I understand what you wrote, you are giving it:

gcc source.c -g -o a a.o

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www:~$ gcc test.c -g -o a
www:~$ gdb a
GDB is free software and you are welcome to distribute copies of it
 under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for details.
GDB 4.14 (i486-slackware-linux), Copyright 1995 Free Software Foundation, Inc...
(gdb) l
1       #include <stdio.h>
3       int main(void)
4       {
5               int i;
7               printf("<HTML>\n");
8               printf("<BODY>\n");
9               for(i=0; i<50000; i++){
(gdb) break 7
Breakpoint 1 at 0x80004a6: file test.c, line 7.
(gdb) run
Starting program: /users/joe/a

Breakpoint 1, main () at test.c:7
7               printf("<HTML>\n");
(gdb) n
8               printf("<BODY>\n");
v5Author Commented:
I forgot -g

One more question, when I set break point at line 6, how can I display the value of the variable at that line?

Another question, in your opinion, which debugging tool is the greatest? dbx, gdb, X version of gdb, or purecov?

To get the value of a location, use the inspect command:

(gdb) inspect i

In my opinion, dbx and gdb are about the same.  xgdb is maybe a little easier to use but you can't always count on having it available.  I've never used purecov.

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