CODEWITHSUNDEEP
cgdb
Mikey
Mikey

Reputation: 21

How do I display the last variable update while single stepping in gdb

If a C program is something like:

void main ()
{
    int a, b, c;
    a = 1;
    b = a + 1;
    c = b + 1;
}

while running gdb, and single stepping:

How do I display the variable that got updated by that single step? Of course this is a highly simplified example, the idea being trace the execution. Something like:

(gdb) step
         a=1
(gdb) step
         b=2
(gdb) step
         c=3

Thanks

Upvotes: 1

Views: 387

Answers (3)

bruceg
bruceg

Reputation: 2513

The closest thing that gdb has to this is setting a watch for a variable. GDB will break every time a watched variable is changed. GDB: Watch a variable in a given scope for example

Upvotes: 0

2785528
2785528

Reputation: 5566

gdb has an option that causes it to display 6 panels.

The upper right panel displays locals or registers.

(gdb) step
      a=1

With this display, the line a=1 is the next line to be executed.

How do I display the variable that got updated by that single step?

In the 6 panel display, the variable a is displayed, (and since you did not initialize it, any value might show prior to the step) and when you step, the 'a' value is updated.

In emacs, the command is (setq gdb-many-windows t), and I am confident the gdb manual can identify the command line equivalent.

--- might be related to "layout regs"

Upvotes: 1

Fantastic Mr Fox
Fantastic Mr Fox

Reputation: 33854

This cannot be done automaticly, imagine a line where you step that loks like this:

int a = someFunction(b++, c--);

a, b, and c change (along with any number of global or static variables affected by someFunction). How would GDB know what to print? You can use the print command to show a variables value.

Upvotes: 0

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