Why does this crash TextPad?

[terrypin]

The following removes the right hand bracket from lines like these:
96)
106)
229)

Find what: \)
Replace with: (empty)
(Regex enabled)

But on my first attempt I added an unnecessary '?', i.e:
Find what: \)?

Why did that not only fail to work but consistently crashed TP?

[bbadmin]

We can't reproduce this behaviour with TextPad 8.12.0. Is this the version you are running?

Can anyone else reproduce it?

[AmigoJack]

Can confirm with 8.4.2x64 on Win7x64 that "Replace All" will make TextPad unresponsive forever (endless loop?), but not directly crash.

[terrypin]

Thanks both. This is TextPad 7.6.4 (64-bit Edition), running in Win 10 Version 20H2 (OS Build 19042.1706)

It not only becomes unresponsive here but also prevents access to any other apps. Task Mgr does eventually open but that too is unresponsive, forcing a Restart. Essentially my definition of a crash!

[MudGuard]

Let's say we start the replacement at position 0.
\)? matches "nothing", i.e. a String of length 0 (which extends from position 0 to position 0).
This string is then replaced by nothing (which starts/ends at position 0).
The start position for the next search is then placed behind the replacement, i.e. at position 0.

Then \)? matches "nothing", i.e. a String of length 0 (which extends from position 0 to position 0).
This string is then replaced by nothing (which starts/ends at position 0).
The start position for the next search is then placed behind the replacement, i.e. at position 0.

Then \)? matches "nothing", i.e. a String of length 0 (which extends from position 0 to position 0).
This string is then replaced by nothing (which starts/ends at position 0).
The start position for the next search is then placed behind the replacement, i.e. at position 0.

Then ...

it might take a while :D to get to another position ...

[ben_josephs]

The current version of TextPad protects against this endless loop in Replace All by advancing the cursor after matching an empty string. Older versions didn't.

There are two morals here:
1. avoid regexes that match empty strings;
2. use the current version of TextPad.

[terrypin]

Thanks both.

Appreciate that detailed explanation, MudGuard, but confess I don't understand 'position 0'? At the start of a line, surely the text cursor is always at position 1?

[ben_josephs]

MudGuard counts from 0, as do most programmers and mathematicians (although, when not programming, from long-standing habit, even they usually count lines and character positions from 1).

[AmigoJack]

as do most programmers and mathematicians

That's why cups of them say "World's #0 programmer".