[xdebug-general] Re: Tracing line by line

Hi Алексей,

On Mon, 21 Dec 2009, Алексей Шеин wrote:

> First, I'd like to thank you for your excellent work! Xdebug really helps me
> a lot :)
> I've got a question:
> Say I have the following code
> <?php
> $i = 10;
> $i +=
> ++$i
> + $i
> + $i++;
>
> print $i;
> ?>
>
> How can I trace it line by line, i.e. I want to know how $i changes its
> value from line 3 to 7, for now it's just 10 and 45 at one step. Is it
> possible?

Xdebug's debugger current stops everytime PHP encounters the end of a
statement (the EXT_STMT opcode). If we look at your snippet, it is
generated a few times:

line # op fetch ext return operands
-------------------------------------------------------------------------------
   2 0 EXT_STMT
         1 ASSIGN !0, 10
   5 2 EXT_STMT
         3 PRE_INC $1 !0
   6 4 ADD ~2 $1, !0
         5 POST_INC ~3 !0
         6 ADD ~4 ~2, ~3
         7 ASSIGN_ADD 0 !0, ~4
   8 8 EXT_STMT
         9 PRINT ~6 !0
        10 FREE ~6
  10 11 EXT_STMT
        12 RETURN 1

But not for everyline. Xdebug in SVN
(http://xdebug.org/docs/install#source) provides a function call
"assignment tracing" which provides the following output:

derick[@]kossu:~$ php -dxdebug.collect_assignments=1 -dxdebug.auto_trace -dxdebug.trace_format=0
<?php
$i = 10;
$i +=
    ++$i
    + $i
    + $i++;

print $i;
?>
45

derick[@]kossu:~$ cat /tmp/trace.124683842.xt
TRACE START [2009-12-22 00:27:31]
    3.5909 654472 -> {main}() /home/derick/-:0
                         => $i = 10 /home/derick/-:2
                         => $i += 33 /home/derick/-:6
    3.5918 8280
TRACE END [2009-12-22 00:27:35]

But as you see, this doesn't catch the pre and post inc operators yet —
that should be handled properly though. I added a bug for this so that I
don't forget to add it.

with kind regards,
Derick

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