Alphabetizing a file?

This is a discussion on Alphabetizing a file? within the C Programming forums, part of the General Programming Boards category; Another quick thing I need some assistance with is alphabetizing a file created from the program. So, the program will ...

  1. #1
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    Alphabetizing a file?

    Another quick thing I need some assistance with is alphabetizing a file created from the program. So, the program will create a file like:

    Namath Joe
    Lugo Julio
    Favre Brett
    Jordan Michael

    And I need to put the file in terms order of last name:

    Favre Brett
    Jordan Michael
    Lugo Julio
    Namath Joe

    I can only store one line of data at a time though in the program.

  2. #2
    Deathray Engineer MacGyver's Avatar
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    So store each name in memory and then compare them and reorder them.

    There are many ways of sorting, including some sorting algorithms already implemented in C. All you would have to do is write a function to compare one string with another, and that's even done for you, too.

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    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by TitoMB345 View Post
    I can only store one line of data at a time though in the program.
    You will have to change that because holding more than one line in memory at a time is the ONLY way to do it.
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    Quote Originally Posted by iMalc View Post
    You will have to change that because holding more than one line in memory at a time is the ONLY way to do it.
    Couldn't he just store the first sentence in the file in memory and then look at the first letter in the next to determine if it has to move or stay?

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    Quote Originally Posted by Neo1 View Post
    Couldn't he just store the first sentence in the file in memory and then look at the first letter in the next to determine if it has to move or stay?
    Yeah, you could STORE one line, and read in partials of the next line. However, unless it's GUARANTEED that all names start with different letters, you can't just read one letter. You also have to read the file multiple times to eventually come out with the lines in the right order, because the first thing you read may well be the LAST thing to output, and you'd have to have some sort of indication of which lines have already been processed [opening the same file twice with different FILE pointers MAY work - but some environments require special tricks to open the same file twice].

    Consider:
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    Yeah, I still havent been able to find a way to do this. It seems nearly impossible without the ability to store all the data in the program, it would be easy if this were possible. But I am not allowed. I am completely stuck.

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    Quote Originally Posted by iMalc View Post
    You will have to change that because holding more than one line in memory at a time is the ONLY way to do it.
    Nah. He could just use merge sort, using temporary files. That's how big tape-drive machines used to sort things without needing memory.

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    So, reading through my C text, it seems somehow I will have to use fseek(). I think my original approach to the problem was incorrect. I am going to start over and try another way.

  9. #9
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by TitoMB345 View Post
    So, reading through my C text, it seems somehow I will have to use fseek(). I think my original approach to the problem was incorrect. I am going to start over and try another way.
    You should not have to seek. In fact, I don't see how you could, since this data is line-based and lines can be of different lengths.

    I still suggest using a file-based merge sort. It's not hard. Same as any other merge sort, except that the spot in the algorithm where you allocate memory, you just open a file instead.

    EDIT: And with a small adjustment to account for the fact you don't know how much data you have.

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    Quote Originally Posted by brewbuck View Post
    You should not have to seek. In fact, I don't see how you could, since this data is line-based and lines can be of different lengths.
    u can seek in the file with variable string lengths..... just use ftell() and store the position before and after seeking and store them in a long int..... string compare and rewrite......

    a part of u r code would be......
    Code:
    c  =  ''  ;/*nocharacter*/
    
    while(  ! feof (  file_poin  )  )
    {
    
                 first_word_start  =   ftell ( file_poin ) ; 
                 
                 fgets ( first_name , file_poin ) ;   /*first name*/
                 
                 first_word_end   =   ftell( file_poin  )  ;
    
                 fgets ( second_name , file_poin ) ;   /*second name*/
    
                 second_word_end = ftell(  file_poin  ) ;
                 
                  if (    strcmp   ( first_name , second_name )   >  0  )
    
                                      {
    
                                           fseek(  file_poin , first_word_start  ,  0   )  ;  
    
                                           fputs (  first_name , file_poin );
    
                                                           while(   ftell (  file_poin  )  !=  first_word_end  ) 
                                                              {
                                                                   putc( c , file_poin );
                                                               }            
                                                              
                                            fputs ( second_name , file_poin ) ;  
    
                                                            while(   ftell  ( file_poin  )  !=  second_word_end )  
                                                               {
                                                                   putc( c , file_poin );
                                                               }  
    
                                           rewind( file_poin );
                                       }
    }

    as only swapping is taking place there wont be extra spaces or alphabets after each swap
    Last edited by ElemenT.usha; 11-07-2007 at 03:28 PM. Reason: replacing one char variables with understanable ones

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    Frequently Quite Prolix dwks's Avatar
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    gets() is a bad idea. (Besides, gets() reads from stdin, and I think you want to read from p. Consider fgets().) You're missing a semicolon. Your indentation is non-existent. You're using while(!foef()). All of your variable names are an unreadable one character long. Oops.
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    Quote Originally Posted by dwks View Post
    gets() is a bad idea. (Besides, gets() reads from stdin, and I think you want to read from p. Consider fgets().) You're missing a semicolon. Your indentation is non-existent. You're using while(!foef()). All of your variable names are an unreadable one character long. Oops.
    ya code has been changed......sorry for inconvenience
    im used to one characters...... and indenting is way toooo far.......

  13. #13
    Frequently Quite Prolix dwks's Avatar
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    Yeah, well, there's no need to use quite that much whitespace. Too much is as bad as too little. Well, maybe not quite as bad.

    Oh, one other thing: passing fseek() 0 for the whence parameter is a little unportable, not to mention difficult to understand. SEEK_SET is much easier to understand than 0, don't you think?

    im used to one characters...... and indenting is way toooo far.......
    You should get out of the habit of using one-character names, then. And I'm not surprised that you think that's too far. I think it's too far, too.
    dwk

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    Quote Originally Posted by dwks View Post
    Yeah, well, there's no need to use quite that much whitespace. Too much is as bad as too little. Well, maybe not quite as bad.

    Oh, one other thing: passing fseek() 0 for the whence parameter is a little unportable, not to mention difficult to understand. SEEK_SET is much easier to understand than 0, don't you think?


    You should get out of the habit of using one-character names, then. And I'm not surprised that you think that's too far. I think it's too far, too.
    yes SEEK_SET or SEEK_BEG would be better.....
    but i dont think 0 should be a problem.....
    thanxxx for the suggestion.....


    and............


    is your name DWK????

  15. #15
    Frequently Quite Prolix dwks's Avatar
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    For fseek(), one should use the ANSI-standard SEEK_SET, not SEEK_BEG, which as far as I can tell is for seek().

    On most compilers, 0 wouldn't be a problem. But I'm not sure if SEEK_SET is guaranteed to be 0 or not. It probably is -- I've seen lots of code like yours.

    No, my name isn't DWK. Is yours "ElemenT.usha"?
    dwk

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