I'm working on a school project written in Objective-C, but hopefully this is a simple thing...

I have an XML document. I need to go into that document, find instances of timecode (like 00:01:22:12) and replace them with a string, like "foobar". The timecode will always be different numbers, but always in the same format.

My problem is I've never done regEx in C before... anyone know how this is done?

Show examples of your data. If the data cannot be unambiguously determined, a regex will be difficult if not possible.

Don't bother with regex. Read the XML file line-by-line and use sscanf() to replace the timestamp with the desired alternative. If the name of the XML element preceding the timestamp is constant and unique, you could even use strstr() to get where the stamp starts and ends and modify it from there.

I started writing an example use of <regex.h> and then I realized it's too much work for something that can be easily avoided.

A sample xml file would indeed help.

And if those times appear in different tags?

Are you sure pattern matching is robust enough? Since you're using some XML data, shouldn't you be parsing the XML and locating the relevant data that way?

One of the reasons to use XML in the first place is to provide structure that allows you to find your data. Having said that, perhaps using R-E's is part of your assignment. In that case, you would use the functions declared in regex.h. For the full explanation of regex usage in C,
A previous thread on the subject may be illustrative.
The basic premise is that your code contains a literal (or other, I guess) string containing a regular expression notation. This string is then 'compiled' and the resulting handle is used to reference the compiled regex in one or more searches of a specified buffer.
Now, there is another alternative which I think is loads more fun and instructive, and that is to write a simple lexical analyzer using lex. This generates C code, which you compile, link, & run against your XML file(s).
--- rod.

Sounds great to me, if I can avoid regEx I will gladly do so. This is a group project, and I'm not the one generating the XML file, and I don't have the XML file in front of me right now, but here is the kind of data we would we doing:

<KEY>media start</KEY>
<STRING>in 00:01:23:22</STRING>
<KEY>media end</KEY>
<STRING>out 00:01:45:15</STRING>

and so on. it would all be very standardized; the value for "media start" would ALWAYS be "in ##:##:##:##" for instance. So what you're saying sounds like it's the way to go. I will look into sscanf() but if you want to post an example or suggestion, you're welcome to do so!

Thanks for all the help guys, I appreciate it.