How should I read this file (i/o question)

This is a discussion on How should I read this file (i/o question) within the C Programming forums, part of the General Programming Boards category; Well I studied and knew c well about three years ago, since then, java has rotted my brain and I ...

  1. #1
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    How should I read this file? (i/o question)

    Well I studied and knew c well about three years ago, since then, java has rotted my brain and I need some help.

    What I'm doing is opening a file (see below) and writing 3 coordinates into an array. The only problem is there are 'j' or 'J' charecters that seperate some of the coordinates. I need to know how to read the file while ignoring the j charecters.

    Code:
    J
       366 -1722   583
       366   356  1783
       866   789  1033
       866 -1289  -167
       366 -1722   583
    J
      -500 -1472   150
         0 -1039  -600
         0  1039   600
      -500   606  1350
      -500 -1472   150
    J
       366   356  1783
      -500   606  1350
         0  1039   600
       866   789  1033
       366   356  1783
    My main problem is that I have 4 files to read and there are not always 5 sets of coordinates in between each 'j' so Im unsure how to ignore the j.

    Any ideas of how to read this type of file?
    Last edited by mmattax; 01-16-2006 at 03:13 PM.

  2. #2
    Sr. Software Engineer filker0's Avatar
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    Lots of ways to do this.

    If you use fgets() to read a line into a buffer, check the first character to see if it's 'j' or 'J', and if it is, ignore the line. This is probably the easiest.
    Insert obnoxious but pithy remark here

  3. #3
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    LOOP:

    if ( returnValueFromFile != 'j' )
    SaveCoordinates;

    ?

  4. #4
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    I'll try those suggestions and post any problems, thanks.

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    Ok, I am now using fgets(), and havea condition to ignore the 'j' charecters.

    But if it doesn't read a 'j' I am having trouble isolating the 3 int values on that line, is there an easy way to read those?

  6. #6
    ~viaxd() viaxd's Avatar
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    it does read 'J' and only then you check if it's a 'J' and ignore it, like this:
    Code:
    char buf[64];
    while (fgets(buf, sizeof buf, fp) != NULL)
    {
      if (buf[0] == 'J' || buf[0] == 'j')
        continue;
      else
      /* do stuff */
    }
    :wq

  7. #7
    Registered User Tonto's Avatar
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    He said he had that and needed to isolate the int values viaxd. Perhaps sscanf(..) is appropriate here?

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    Quote Originally Posted by viaxd
    it does read 'J' and only then you check if it's a 'J' and ignore it, like this:
    Code:
    char buf[64];
    while (fgets(buf, sizeof buf, fp) != NULL)
    {
      if (buf[0] == 'J' || buf[0] == 'j')
        continue;
      else
      /* do stuff */
    }

    I had all of this. I just do't know how to read the numbers now because the Strings look like " 366 -1722 583" so im unsure how to isolate the digits and not the spaces.

    any ideas?

    Thanks for your help.

  9. #9
    Sr. Software Engineer filker0's Avatar
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    Code:
    long val1, val2, val3;
    
    ...
    if (sscanf(buf, "%d %d %d", &val1, &val2, &val3) < 3)
    {
         /* didn't get all three values ... */
         ... handle error condition ...
    }
    else
    {
        ... do something with val1, val2, and val3 ...
    }
    Last edited by filker0; 01-16-2006 at 04:35 PM. Reason: was missing a '&'
    Insert obnoxious but pithy remark here

  10. #10
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    Thanks, I had no clue that sscanf exisited. Thats a pretty sweet function!

    Thanks for all the help guys!

  11. #11
    Cached User mako's Avatar
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    shudn't it be fscanf? I'm prolly wrong here, I just don't happen to know sscanf personally...

  12. #12
    ATH0 quzah's Avatar
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    While you could use fscanf, a better pair is fgets to read the line, and then sscanf to extract the data. While it may seem like more work, it's usually better, because now you have (guarinteed, save for some EOF or error with your file getting deleted while you're using it, etc...) for sure the entire line in a buffer. Where as if you just use fscanf, and it reads part of its conversions, but not all, you have to wonder where exactly in your file you are now.


    Quzah.
    Hope is the first step on the road to disappointment.

  13. #13
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by filker0
    Code:
    long val1, val2, val3;
    
    ...
    if (sscanf(buf, "%d %d %d", &val1, &val2, &val3) < 3)
    This either needs to be int, or the directives should be %ld.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  14. #14
    Sr. Software Engineer filker0's Avatar
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    Quote Originally Posted by Dave_Sinkula
    This either needs to be int, or the directives should be %ld.
    You're quite right. My bad. I had originally typed it as %ld, then went back and amended it to %d to make it less a complicated example to understand, however I forgot to fix the declaration at the top.
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