getw/putw problem

This is a discussion on getw/putw problem within the C Programming forums, part of the General Programming Boards category; I tried to write/read a line of intergers(like 12345) to a file using getw, but I don't know how to ...

  1. #1
    Registered User fenikkusu's Avatar
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    getw/putw problem

    I tried to write/read a line of intergers(like 12345) to a file using getw, but I don't know how to stop the input loop, like this:

    Code:
    #include<stdio.h> 
    int main(void)
    { 
      FILE *f1,*f2,*f3; 
      int number; 
      printf("Content of the data file\n"); 
      f1=fopen("data","w"); 
    
      while((number=getw(stdin))!='\n')
       putw(number,f1);
    
      fclose(f1); 
      
      f1=fopen("data","r"); 
      f2=fopen("odd","w"); 
      f3=fopen("even","w"); 
      
      while((number=getw(f1))!=EOF)/* Read from data file*/ 
      { 
      if(number%2==0) 
       putw(number,f3);/*Write to even file*/ 
      else 
       putw(number,f2);/*write to odd file*/ 
      } 
      
      fclose(f1); 
      fclose(f2); 
      fclose(f3); 
      f2=fopen("odd","r"); 
      f3=fopen("even","r"); 
      
      printf("\n\nContent of the odd file\n\n"); 
      while((number=getw(f2))!=EOF) 
       printf("%d%d",number); 
       
      printf("\n\nContents of the even file"); 
      while((number=getw(f3))!=EOF) 
       printf("%d",number); 
       
      fclose(f2); 
      fclose(f3); 
      getch();
      return 0;
    }
    Please help me consider it

  2. #2
    spurious conceit MK27's Avatar
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    Looks to me like these w() functions are legacy -- why do you want to use them?

    Anyway, if getw() does exactly what it says I would not trust it to find ANY particular character.
    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

  3. #3
    and the Hat of Guessing tabstop's Avatar
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    If getw reads a number (a wild guess based on typing "man getw" into Google), then why would you expect it to ever be \n? According to the man pages I'm seeing (assuming we're even talking about the same thing), getw returns EOF on error.

    I guess you need to decide, how you want the user to stop typing numbers.

  4. #4
    Registered User fenikkusu's Avatar
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    Yeah, that's what I'm considering. I want user to stop typing numbers by pressing enter(suggest some other "smooth" ways?) but getw is only used with intergers

  5. #5
    Kernel hacker
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    Quote Originally Posted by fenikkusu View Post
    Yeah, that's what I'm considering. I want user to stop typing numbers by pressing enter(suggest some other "smooth" ways?) but getw is only used with intergers
    Two simple variants:
    1. Use a "sentry value", e.g. enter 0, -1, -99999999 or some other value that is not in the valid range that can be used as "this is the end of input".
    2. Read the value as a string, and then convert using strtol() or a similar function.

    --
    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.

  6. #6
    Complete Beginner
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    ...or simply ask the user how many numbers he wants to enter and then ask for a number that many times.

    Greets,
    Philip

    PS: while(true); do read a; if [ `echo $a%2 | bc` -eq 0 ]; then echo $a >> even; else echo $a >> odd; fi; echo $a >> data; done;
    Last edited by Snafuist; 02-19-2009 at 04:56 AM.
    All things begin as source code.
    Source code begins with an empty file.
    -- Tao Te Chip

  7. #7
    Registered User fenikkusu's Avatar
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    Quote Originally Posted by matsp View Post
    Two simple variants:
    1. Use a "sentry value", e.g. enter 0, -1, -99999999 or some other value that is not in the valid range that can be used as "this is the end of input".
    2. Read the value as a string, and then convert using strtol() or a similar function.

    --
    Mats
    1.I've changed '\n' into -1 and it doesn't help. dunno
    2.I just want to see how getw works and don't want to resort to string usage here

    @Philip:
    ...or simply ask the user how many numbers he wants to enter and then ask for a number that many times.
    Asking for a number is ok but what I want to know is how getw stops (as scanf stops at the first space/tab/newline)

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