why not to get line number of one file?

This is a discussion on why not to get line number of one file? within the C Programming forums, part of the General Programming Boards category; Code: #include <stdio.h> #include <stdlib.h> #include <string.h> int main( int argc, char **argv) { char *input = argv[0]; FILE *fp; ...

  1. #1
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    why not to get line number of one file?

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    int main( int argc, char **argv)
    {
        char *input = argv[0];
        FILE *fp;
        if ( (fp = fopen(input,"r")) == 0 ){printf("open '%s' error.\n",input); exit(0);}
        int i = 0;
        while( feof(fp) == 0 )
        {
               char buf[100];
               fgets(buf,100,fp);
               if ( strlen(buf) >= 2 ) ++i;
               printf("%s\n",buf);
        }
        printf("line number:%d\n",i);
        return 0;
    }

  2. #2
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    You should give us more info.
    Question 12.2
    Don't use feof() to control loop condition.

  3. #3
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    Quote Originally Posted by Bayint Naung View Post
    You should give us more info.
    Question 12.2
    Don't use feof() to control loop condition.
    Code:
        while( fgets(buf,100,fp) != NULL )
        {
               
               //char *x = fgets(buf,100,fp);
               i++;
               printf("%s\n",buf);
               //fputs(buf, fp);
        }
        printf("line number:%d\n",i);
    get wrong line number, why?
    Last edited by zcrself; 10-14-2010 at 12:50 AM.

  4. #4
    Registered User whiteflags's Avatar
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    Each line ends with newline.
    So count the newlines.
    Extrapolate line numbers from this information.

  5. #5
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    What do you mean by 'can't get line number'?!
    Is it giving you wrong line number or what???

  6. #6
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    Quote Originally Posted by Bayint Naung View Post
    What do you mean by 'can't get line number'?!
    Is it giving you wrong line number or what???
    Yes.

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    Can attach your text file? and post output of your program.

  8. #8
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    Quote Originally Posted by Bayint Naung View Post
    Can attach your text file? and post output of your program.
    program:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    
    int getLineCount(char *input)
    {
        FILE *fp;int i = 0; char buf[100];
        memset(buf,0x00,sizeof(buf));
        if ( (fp = fopen(input,"r")) == 0 ){printf("open '%s' error.\n",input); exit(0);}
        while( fgets(buf,44,fp) != NULL )
        {
               i++;
               //printf("%d %s\n",i,buf);
        }
        return i;
    }
    
    
    int main( int argc, char **argv)
    {
        char *input = argv[0];
        
        
        printf("line number:%d\n",getLineCount(input));
        return 0;
    
    }
    input:
    Code:
    @HWI-EAS-249_38:2:1:2:857.R
    AAAGTATGTAGGACTCATGNNNNTNNNNNNNCNNNNNNAN
    +
    ?8BBBBBBBBBB;BB<'<,'''';'''''''9'''''','
    output:
    Code:
    line number:180
    Last edited by zcrself; 10-14-2010 at 02:08 AM.

  9. #9
    and the hat of wrongness Salem's Avatar
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    > get wrong line number, why?
    Unless you know FOR SURE that every line is <98 characters in length, then you're going to end up counting the number of lines AND the number of 99-character blocks that make up long lines.

    Make sure buf contains a \n before incrementing.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  10. #10
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    Quote Originally Posted by Salem View Post
    > get wrong line number, why?
    Unless you know FOR SURE that every line is <98 characters in length, then you're going to end up counting the number of lines AND the number of 99-character blocks that make up long lines.

    Make sure buf contains a \n before incrementing.
    I can't understand your answer clearly

  11. #11
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    I would declare char buff[] at the top of the function, and NOT inside the while loop.

  12. #12
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    Salem is saying that, if your input file has any line longer than the buffer, the line count will be incorrect. That's because of the way fgets() works when it encounters long lines.

    Read the documentation for more information on how fgets() works.

    Furthermore, if you have an input file with non-text characters, you may get different results too (although counting lines in such a file is rather an academic exercise).
    Right 98% of the time, and don't care about the other 3%.

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