Check the return status of scanf

This is a discussion on Check the return status of scanf within the C Programming forums, part of the General Programming Boards category; This is my code I'm not sure where I've gone wrong or how I do it but I keep getting ...

  1. #1
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    Check the return status of scanf

    This is my code I'm not sure where I've gone wrong or how I do it but I keep getting this message back... Any help would be great.


    75. fscanf(fp, "%d", &check);
    ==> You have not checked the return status of scanf.

    90. fscanf(fp, "%f", &hour);
    ==> You have not checked the return status of scanf.



    Code:
          fscanf(fp, "%d", &check);
          if (feof(fp))
          {
             fclose(fp);
             break;
          }
          fscanf(fp, "%s", stay);
          if (feof(fp))
          {
             fclose(fp);
             break;
          }
          fscanf(fp, "%s", taken);
          if (feof(fp))
          {
             fclose(fp);
             break;
          }
          fscanf(fp, "%f", &hour);

  2. #2
    csd@auth
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    Maybe it is because since you have closed your file you can't read from it.
    For example if the first fscanf succeeds the other won't work.You must fix your code.

  3. #3
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    Why u r using these many of 'if's' for the same purpose in ur program??
    S_ccess is waiting for u. Go Ahead, put u there.

  4. #4
    CSharpener vart's Avatar
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    Message just says what it says - you don't check the return value:
    Code:
    int count = fscanf(fp,"%d",&value);
    if(count != 1)
    {
       //Hey - we have problem with reading from the file
    }
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  5. #5
    and the hat of wrongness Salem's Avatar
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    > fscanf(fp, "%d", &check);
    Meaning it should be

    if ( fscanf(fp, "%d", &check) == 1 )
    // it was successful.
    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.

  6. #6
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    Quote Originally Posted by maven
    Why u r using these many of 'if's' for the same purpose in ur program??
    How would you recommend doing it?

    Thanks for the help on the returning scanf I realise my mistake now.

  7. #7
    Frequently Quite Prolix dwks's Avatar
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    Since || is short-cutting, you could do something like this:
    Code:
    if(fscanf(fp, "%d", &check) != 1 || fscanf(fp, "%s", stay) != 1
        || fscanf(fp, "%s", taken) != 1 || fscanf(fp, "%f", &hour) != 1) {
    
        /* failed */
    }
    Better yet:
    Code:
    if(fscanf(fp, "%d%s%s%f", &check, stay, taken, &hour) != 4) {
        /* failed */
    }
    dwk

    Seek and ye shall find. quaere et invenies.

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  8. #8
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    I tried the second one originally but it gives me a tonne of syntax errors and the first example causes and error in the program (the program freezes) when it tests weather the file has a corrputed float.

  9. #9
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    thats cause you havent provided the rest of the code. The error is there probably

    Im willing to bet you have something like this:

    Code:
    char *stay;
    fscanf(fp, "%s", stay);
    correct?

  10. #10
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    Fixed it... Thanks
    Last edited by Taka; 11-01-2006 at 01:43 PM.

  11. #11
    and the hat of wrongness Salem's Avatar
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    Nice to see you've been listening

    Code:
    char buff[BUFSIZ];
    while ( fgets( buff, BUFSIZ, fp ) != NULL ) {
      if ( sscanf( buff, "%d %s %s %f", &check, stay, taken, &hour ) == 4 ) {
        // Now do your linked list bit
      } else {
        // some error?
      }
    }
    > newnode = (Node*)malloc(sizeof(Node));
    Read the FAQ on casting malloc.
    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.

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