How to find "Range check error" quickly?
lazarus / 12-Debugger

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stephanweber · 2019-06-24 10:37

Hi,

in my Lazarus project I get this runtime error, because I have this
check active in my proj options (-Cr). I have also set "Show debug
info (-vd).


However, how can I also get the code line in which this error happens,
best wo. debugger. This is because currently I have not yet a debugger
installed, and installations are always a bit difficult in my current
Linux setup.
In Delphi I remember something like "goto error" or "find error".

Also with "Show line numbers" or "Show all procs on error" I get no
more hints. The program recovers, because the error pops only up if I
make an integer variable larger than 32K. But also changing the
suspious variables to Int64 does not help.

Bye Stephan

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devEric69 · 2019-06-24 10:52

If you know where is the line (say #num26) that throws this exception,
one method might be to frame it like that, with a "defensive Exception
management", just long enough to understand and correct you bug:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i Try   your-
buggy-line #num26 of code, hereExcept   on E: EOutOfRange do
Application.processmessages; (* <-- you set a breakpoint there, and
you'll inspect your numerical variables, i, strings[j], ..., which are
used by your line #num26, and understand the one that exceeds its
boundary.Once the bug will be fixed, you'll delete the try...except
*)end;

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Martin_fr · 2019-06-24 11:10

-vd will not help at all

You should include "debugger info" (preferably of type "dwarf"):  -gw

You can add  -gl 
then when your running executable hits the error, it should print a
stacktrace with line numbers.
(Run your app from a console, so you see the output / or try the
"view" > "debug windows" > "console output")


I am not sure what your problem is to install a debugger. GDB is
usually easily available for linux.

If your system is intel/amd based, then install the package
LazDebuggerFp.
This gives you a debugger that does NOT need gdb.

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stephanweber · 2019-06-25 13:13

Thanks. I found the problem with some statements like
"Showmessage('here we are: begin of blablabla');"
Now I have to find an infinite loop, which seems to be triggered
randomly (there is indeed a random number generation involved).

Bye Stephan

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Thaddy · 2019-06-26 08:12

If your two issues are related (as they seem to me) use RandomFrom or
RandomRange instead of system.Random.
Also, precisely define define a range as type ( e.g. type myrange i=
3..9 ). That combination will prevent you from making range errors at
run-time.
See: defensive programming in the wiki.
https://wiki.freepascal.org/Defensive_programming_techniques

(reminder to self: upload the rest, finally, lazy b*sta*rd)

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stephanweber · 2019-06-27 12:16

This was very helpful now:

you should include "debugger info" (preferably of type "dwarf"):  -gw

You can add  -gl 
then when your running executable hits the error, it should print a
stacktrace with line numbers.
Run your app from a console!!!

Thanks a lot!!