Thread: Text file parsing

  1. #1
    Registered User
    Join Date
    Aug 2008

    Text file parsing

    I want to learn how to parse text files. Especifically, I want to work with .obj files.

    I have read about the the basics of the obj format, but I'm wondering what standard library functions should I use to read it efficiently. For instance, I want to read the following vertexes

    v 5.672271 1.802055 -5.287645
    v 6.117182 1.802056 5.492141
    v -5.000000 1.803496 4.999999

    into this struct:

    struct vertex
        float x,y,z;
    } vertex_data[num_of_vertexes];
    Could someone give me an example of what functions I could use to do it?

  2. #2
    and the Hat of Guessing tabstop's Avatar
    Join Date
    Nov 2007
    What's wrong with fscanf?

  3. #3
    Registered User
    Join Date
    Sep 2006
    Just a note from the peanut gallery here, but this sounds like a "roll your own", to me.

    I've never heard of a standard library in C for this.

    Sounds too simple to build a library just to import some a char, and 3 numbers.

    Do you want help putting the values into your struct w/o a library?

  4. #4
    Registered User
    Join Date
    Aug 2008
    By standard library I mean stdio, stdlib, etc. I'm an occasional programmer so I'm still learning about so sometimes I'm just not sure which function to use. I did read the scanf, fscanf and sscanf documentation, that was very helpful.

    After looking at some examples of parsing text files, here's what I am using:

        char line[2048];
        while (fgets(line, 2048, fp))
        /* get a face */
        if (!strncmp(line, "f ", 2))
    	sscanf(line+2, "%d/%d/%d %d/%d/%d %d/%d/%d", &args ... )
    However that leads me with a problem. If the program encounters a face like
    f 1/2/3 3/4/5 6/7/8 it reads fine, however f 1//3 3//5 6//8 will trash my data harvest. Any ideas how to deal with this?

  5. #5
    spurious conceit MK27's Avatar
    Join Date
    Jul 2008
    segmentation fault
    Hmm. You can include dud characters in a (s)scanf line with the * flag. That means those items are not placed into a variable:

    scanf("%d%*[/]%d", &x,&y)
    x and y get a number, %*[/] should read any number of / and discard them.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  6. #6
    Make Fortran great again Epy's Avatar
    Join Date
    Sep 2009
    California, USA
    use fscanf or strtok

  7. #7
    Registered User ssharish2005's Avatar
    Join Date
    Sep 2005
    Cambridge, UK
    use combination oif fgets and sscanf functions

    f 1/2/3 3/4/5 6/7/8 it reads fine, however f 1//3 3//5 6//8 will trash my data harvest. Any ideas how to deal with this?
        if( sscanf( str, "%*c %d%*[/]%d %d%*[/]%d%*s", &i,&j,&k,&l) == 4 )
            printf("%d %d %d %d\n", i,j,k,l );
    Life is like riding a bicycle. To keep your balance you must keep moving - Einstein

  8. #8
    ATH0 quzah's Avatar
    Join Date
    Oct 2001
    while( (c=fgetc( in )) != EOF )
        if( isdigit( c ) )
            store( c );
    Or be lazy, since all you seem to care about in your second post is the individual digits.

    Hope is the first step on the road to disappointment.

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