Help implementing file modifcation algo.

This is a discussion on Help implementing file modifcation algo. within the C Programming forums, part of the General Programming Boards category; Hello i m relatively new to programming and i want to implement the following algorithm. 1. accept the directory path ...

  1. #1
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    Help implementing file modifcation algo.

    Hello i m relatively new to programming and i want to implement the following algorithm.

    1. accept the directory path at command prompt
    2. open the directory and scan it for files of my interest (.drg)
    3. when the matching file is found scan it untill the @ character is found at newline.
    4. remove that whole line untill the EOF and save the file.

    So far i have successfuly coded the first 2 steps and also i can detect if the matching file ( with extension .drg ) is found but i cant figure out how to proceed. I would like to know the functions matching best for my need and i would try to code the next steps myself , as that will give me some good practice.

    And i have one more question :
    what is the best way to modify the file and save it ?

    I guess , for my specific task i willl have to copy all the contents untill newline and @ character is found and save it to another temp file. Then delete the original file and rename temp file to original filename . Is this approach the best ?

    Regards
    EnLi

    Edit : forgot to add my working environment ..which is DOS from XP and i m using Dev cpp as my compiler .
    Last edited by enli; 05-04-2008 at 11:34 PM. Reason: Wanted to add OS conditions !1

  2. #2
    CSharpener vart's Avatar
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    I guess , for my specific task i willl have to copy all the contents untill newline and @ character is found and save it to another temp file. Then delete the original file and rename temp file to original filename . Is this approach the best ?
    This is the only portable approach

    there are some other solutions for truncating files platform dependent
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

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    Hi.. could you please point me to those truncating solutions ?
    I googled it but i couldnt find them .

    Also i need some ideas on how to implement my algorithm steps 3 and 4

    Thanks
    EnLi

  4. #4
    CSharpener vart's Avatar
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    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

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    thanks vart .. no offence but i could search for file truncate.. but i m necessarily interested in my solution to my current problem .

    Never mind i will figure out that myself
    Last edited by enli; 05-05-2008 at 11:34 PM. Reason: typo

  6. #6
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    Quote Originally Posted by enli View Post
    thanks vart .. no offence but i could search for file truncate.. but i m necessarily interested in my solution to my current problem .

    Never mind i will figure out that myself
    And the third item on that search is this, which would be the right solution on Linux/Unix:
    http://linux.die.net/man/2/truncate

    Adding "windows" to the search gives this as the first hit :
    http://discuss.fogcreek.com/askjoel/...74&ixReplies=7

    If you are using a different platform, then perhaps appending that would help you out.

    You may not get the FULL story from those links, but it should at the very least be sufficient to ask further questions in more detail.l

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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    Thanks matsp.. i also got that page in my previous queries.. but i didnt look the sencond webpage thorughly. It seems that the function SetEndOfFile() can do that.

    I m looking about that ..and i will keep you updated.

    Much appreciated
    EnLi

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    Ok ..the following sample program does what i was looking for . Hope this might help some needy.

    Code:
    /*
    *   Title        : File truncation
    *   Description  : This little program shows how to truncate a file .
    *   Should work on XP(tested), LINUX(not tested)
    *
    *   test.txt file contents were : aaabaaaasdasdasd
    *   after running the program file contents were : aaab    
    *    and file size currectly reported
    *   
    */
    
    #include <stdio.h>
    #include <unistd.h>  // for ftruncate()
    //#include <conio.h> // for getch()
    int main()
    {
        FILE *fp;
        char ch;
        long int file_descriptor;
        int currpos;
        if((fp=(fopen("test.txt","r+")))== NULL) // file should be opened with write permission
            perror("File Read error");
        
        while((ch=getc(fp))!='b')           // move fp untill 'b' is found
        {}
             
        file_descriptor=fileno(fp);       // get file descriptor
        currpos=ftell(fp);                // get the desired file size
        
        //Setting new file size
        if(ftruncate(file_descriptor,currpos) == 0)
            printf("\n\nFile succesfuly truncated");
         else
            perror("File truncation ERROR : ");       
        fclose(fp);
        //getch();
        return 1;
    }
    Last edited by enli; 05-06-2008 at 05:13 AM. Reason: typo

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