Lua: Find hex-value in string

Question

I'm trying to find the hexadecimal non-printable character 00h within a string with Lua. I tried it with an escape character and as a result I get the same location I start in (that's a printable character). I fiddled around with the character classes, but that didn't amount to anything. My approach looks like this:

location = string.find(variable,"\00",startlocation)

I also tried it this way, but no luck:

location = string.find(variable, string.char(00),startlocation)

How can I find this non-printable pattern in Lua?

Did you try location = string.find(variable,"\0",startlocation) with a single zero? — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Jan 27, 2012 at 10:56
shouldn't you use %z for zero characters in patterns (at least in 5.1) ? — jpjacobs
– jpjacobs, Commented Jan 27, 2012 at 11:10
Yes, I did that, too. I found my mistake. "variable" is filled 00h. I thought I started at a printable character, but in fact I didn't. That's why "location" ended up being the same value as "startlocation", leading me to believe I somehow didn't use the correct representation of 00h in the string.find-command. Thanks to lhf for actually leading me to the right conclusion. — Zerobinary99
– Zerobinary99, Commented Jan 27, 2012 at 11:12

lhf · Accepted Answer · 2012-01-27 10:56:28Z

2

It works fine for me:

> return string.find("one\0two\0,three","\0,")
8   9
> return string.find("one\0two\0,three","\0")
4   4
> return string.find("one\0two\0,three","\00")
4   4
> return string.find("one\0two\0,three","\00",6)
8   8

answered Jan 27, 2012 at 10:56

lhf

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4 Comments

Zerobinary99 Over a year ago

Hmm, must be an error in my code then. I need to check the other variables.

lhf Over a year ago

@Zerobinary99, string.char(00) returns a string of length 1 whose only byte is 0 and this is exactly what "\0" is. Try print(string.char(00)=="\0").

Zerobinary99 Over a year ago

I just tested that out myself ;) Hence the edit of my initial message. Thought I could correct my false assumption before you saw it, but you were faster ;)

daurnimator Over a year ago

Note that \0 isn't valid in a pattern in lua 5.1; use %z.

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