Files problem

This is a discussion on Files problem within the C Programming forums, part of the General Programming Boards category; I am doing a assignment where i have to read the numbers in a file into arrays so if i ...

  1. #1
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    Files problem

    I am doing a assignment where i have to read the numbers in a file into arrays so if i had 3 on line 1 and 2 and line 2, it would be array[0]=3 and array[1]=2.

    But i am having a problem (im new so it may be a simple question)

    Code:
    #include <stdio.h>
    
    main() {
           FILE *fp;
           int hour;
           
    fp   = fopen("payrates.dat", "r");  /* input file - read mode */
      if (fp == NULL)
      {
        printf("input file not opened");
        
      }
      
      fscanf(fp, "&#37;d\n", hour);
      printf("%d", hour);
    }
    thats my code, im basically trying to just the get first number in the file but its giving me 0.00000 or 53 or a long number. Anyone can help me out??

    edit: i also just realized i have the same topic name as signpost's thread i didnt know until after i made it
    Last edited by bigmac(rexdale); 11-27-2007 at 07:17 PM.

  2. #2
    Jack of many languages Dino's Avatar
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    main() is usually declared as returning an integer. When main() exits, it should specify a return code. If your input file does not open properly, it should probably exit too, instead of falling through to your fscanf().

    Todd

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    thats what my if statement would display though if the file was opened or not. but its goes through and displays whats in the hours variable which is the bottom printf.

  4. #4
    Jack of many languages Dino's Avatar
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    See this online reference: http://www.cppreference.com/stdio/fscanf.html

    What is fscanf() returning?

  5. #5
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    A integer number from the payrates.dat file.

  6. #6
    Jack of many languages Dino's Avatar
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    Wrong answer. Put some error checking into your program and repost. Test the return value of fscanf please.

  7. #7
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    I get a minus 1 (-1)

    Code:
    #include <stdio.h>
    
    main() {
           FILE *fp;
           int hour, check;
           
    fp   = fopen("payrates.dat", "r");  /* input file - read mode */
      if (fp == NULL)
      {
        printf("input file not opened");
        
      }
      
      check = fscanf(fp, "&#37;d\n", hour);
      fclose(fp);
      printf("%d", check);
    }

  8. #8
    and the Hat of Guessing tabstop's Avatar
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    It's not clear from what I'm seeing whether your file is opening correctly. Is it?

    Also: just like scanf, fscanf takes its argument by address, not by value. If your file is opening correctly and not empty, this is almost certainly your difficulty here.

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    Ya, i dont think it is because i added a fprint to see if i can print soemthing into the file and it doesn't

    Code:
    #include <stdio.h>
    
    main() {
           FILE *fp;
           int hour, check;
           char line[56];
           
      fp = fopen("payrates.dat", "a");  /* input file - read mode */
      if (fp == NULL)
      {
        printf("input file not opened");
        
      }
      printf("Enter a line: ");
      gets(line);
      fprintf(fp,"&#37;s\n", line);
      check = fscanf(fp, "%d\n", hour);
      fclose(fp);
      printf("%d", check);
    }

  10. #10
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by bigmac(rexdale) View Post
    Ya, i dont think it is because i added a fprint to see if i can print soemthing into the file and it doesn't
    Well, you should know. Does the line "input file not opened" print? If so, it didn't open. If not, then it did.

    Can you find a "payrates.dat" file in your directory, somewhere? Is your program ending abnormally? (My copy of your program did, because I ignored the compiler warning about line 17.) If so, the output might not get written before the crash. Fix line 17 (you need an ampersand in front of hour) and see what happens.

  11. #11
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    Code:
       #include <stdio.h>
       main() {
          FILE *fp;
          char filename[81];
          double line[9], i = 0;
          fp = fopen("payrates.dat", "r");
          if (fp == NULL)
             printf("Cannot open &#37;s\n", filename);
          else {  
             do {
             i++;      
             fscanf(fp, "%lf\n", &line[i]);
             printf("%.2lf ", line[i]);  
             } while (i != 10);
             /*do {
                printf("Enter a line: ");
                gets(line);
                if (line[0] != '\0')
                   fprintf(fp,"%s\n", line);
             } while (line[0] != '\0');*/
             fclose(fp);
          }
          printf("\n%.2lf", line[3]);
          /*i = 2 * line;*/
       }
    ya the ampersand works, but i need it to store the numbers in the file into an array now
    Last edited by bigmac(rexdale); 11-27-2007 at 09:00 PM.

  12. #12
    and the hat of wrongness Salem's Avatar
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    Read the FAQ on why gets() is bad, REALLY bad.
    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.
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  13. #13
    Frequently Quite Prolix dwks's Avatar
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    > Read the FAQ on why gets() is bad, REALLY bad.
    To be precise: http://faq.cprogramming.com/cgi-bin/...&id=1043284351

    Code:
             fscanf(fp, "&#37;lf\n", &line[i]);
             printf("%.2lf ", line[i]);
    For doubles, one uses %lf in scanf(), but %f in printf()! %lf doesn't exist with printf(). printf() uses %f for both floats and doubles. Confusing, no?

    main() should also return a value. The implicit int rule that you're using is deprecated. Use int main() and add return 0 if you wish as well. There's another FAQ entry on this. http://faq.cprogramming.com/cgi-bin/...&id=1043284376
    dwk

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