Regular expressions

This is a discussion on Regular expressions within the C Programming forums, part of the General Programming Boards category; Hi there; I know what regular expressions are, and have used very simple ones before - but I don't know ...

  1. #1
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    Regular expressions

    Hi there;

    I know what regular expressions are, and have used very simple ones before - but I don't know if they can be used in C, or how to use them. I do know, though, that regex would save me a heck of a lot of trouble in parsing a slightly regular string (tokenising).

    What I am doing, is checking for the following regular expression:

    anystring*$anyint,*$anyint,*$anyint

    Where there is a *, there can be any number of whitespace.

    I suppose I am going against cboard ettiquette here and asking for a bit of a write out, but I don't know where to start looking (as I asked before, I don't even know if regex can be used in C).

    Googling attempts seem to throw 1000s of C++ string regex functions at me but no C..

    Thanks.

  2. #2
    and the hat of wrongness Salem's Avatar
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    Just use a library - example http://www.pcre.org/
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    Regular expressions are nice, but I don't think I'd use a library to deal with whitespace. You could easily just use a C function like sscanf() that will ignore whitespace. Something like:

    Code:
    const char line[] = "blah  123,     456,   789";
    char str[50];
    int i1, i2, i3;
    
    sscanf(line, "%s %d, %d, %d", str, &i1, &i2, &i3);
    
    printf("anystring: %s\n"
           "anyint1: %d\n"
           "anyint2: %d\n"
           "anyint3: %d\n", str, i1, i2, i3);
    or if you were reading from a file, you could use fscanf() which is the same thing, but it uses a file for its first parameter. In a way, C has functions that use a regular expression, like sscanf, but it's just not as complex as something like Perl style regex's. So I'd suggest looking more into the different string functions C. Anyway, good luck.

  4. #4
    Mad OnionKnight's Avatar
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    $ in a regex is the end of line anchor. You sure that's what you want?

  5. #5
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    hmm, I just figured he didn't know much about regular expressions and meant that those were variables. I think those *'s would more likely become \s+ if it was a real regular expression also.

  6. #6
    Registered User ssharish2005's Avatar
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    NOTE:
    Code:
    * represents -> 0 or more elements Ex: set{E, a ,aa,aaa,aaaa,.....} where Ereprents empty string
    
    + represents -> 1 or more elements Ex: set{a,aa,aaa,aaaa,....}
    ssharish2005

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