Better scanning method

This is a discussion on Better scanning method within the C Programming forums, part of the General Programming Boards category; Say I had a file with the following values in it 100 200 300 400 500 Now I want to ...

  1. #1
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    Better scanning method

    Say I had a file with the following values in it

    100 200 300 400 500

    Now I want to assign a to 100, b to 300 and c to 500. Am I correct in thinking that fscanf has to scan through each one like this?

    fscanf(file,"%d %d %d %d %d",&a,&b,&c,&d,&e);

    There has to be a better way of doing that,without having the needless variables!!!
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  2. #2
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    If that works, why don't you just use it? The whole idea of high level languages like C, is to not write code when someone else has done it for you.

  3. #3
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    Thumbs up

    Here's the way:

    Code:
    # include <stdio.h>
    # include <conio.h>
    
    int main()
    {
    	FILE *fin= NULL;
    	int Numbers = 0;
    
    	fin = fopen("numbers.txt", "rt");
    
    	while (fscanf(fin, "%d", &Numbers) != EOF)
    	{
    		printf("\nNumbers = %d", Numbers);
    	}
    	getch();
    	return 0;
    }
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  4. #4
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    Originally posted by Sean
    If that works, why don't you just use it? The whole idea of high level languages like C, is to not write code when someone else has done it for you.
    ...unless you can do it better, of course
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  5. #5
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    What i'm basically trying to say is that I don't need 200 and 400 so why waste the space by declaring extra variables, especially when in some cases there can be 20+ values in a file and I only want to use 4 of those values for the program. Thanks GaPe but there doesn't seem to be a conio.h in linux
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  6. #6
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    The "conio.h" library is just for the "getch()" command and it is used to stop the program. In this case it is useless.
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  7. #7
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    So does that answer my problem then, taking the conio and getch out of your method just make the program print all the numbers.
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  8. #8
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    Cool

    Yes.
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  9. #9
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    you could try this:

    Code:
    fscanf(file,"%d %*d %d %*d %d", &a, &b, &c);
    the * will cause the input field to be skipped and no assignment will be made.

  10. #10
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    This methode is inefficient. If you want to save your numbers than you should do this with an array of integers.
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  11. #11
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    Originally posted by GaPe
    This methode is inefficient. If you want to save your numbers than you should do this with an array of integers.
    his original question was this:

    Originally posted by pdstatha
    Say I had a file with the following values in it

    100 200 300 400 500

    Now I want to assign a to 100, b to 300 and c to 500. Am I correct in thinking that fscanf has to scan through each one like this?

    fscanf(file,"%d %d %d %d %d",&a,&b,&c,&d,&e);

    There has to be a better way of doing that,without having the needless variables!!!
    mine answers that. yours does not. whether your code is more efficient than what i gave him doesnt really matter in this case.

  12. #12
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    besides, what does yours really do? if he wanted to store the numbers in an array of int, he could do something like this:

    Code:
    #include <stdio.h>
    #include <stdlib.h> //for strtol()
    #include <string.h> //for strlen()
    #include <ctype.h> //for isdigit()
    
    int main(void)
    {
       char  line[1024]; 
       char *endp;
       int   iArray[100] = {NULL};
       int   i, j = 0;
       
       FILE *fileptr;
       
       if((fileptr = fopen("filename.txt", "r")) == NULL)
       {
          printf("Could not open file!\n");
          return 0;
       }
    
       
       while(fgets(line, sizeof(line), fileptr))
       {
          line[strlen(line) - 1] = '\0'; //removes the '\n'
    
          for(i = 0; i < strlen(line); ++i)
          {
             if(isdigit(line[i]))
             {
               iArray[j++] = strtol(&line[i], &endp, 10);
               while(isdigit(line[i])) ++i;
             }
          }
       }
       for(i = 0; i < j; ++i)
          printf("%d ", iArray[i]);   
    
       fclose(fileptr);
       getchar(); //not needed if run from command prompt
       return 0;
    }
    EDIT: bah, i should really compile these things first.
    EDIT2: oops, didnt include 0 as a number that may show up in the file... not good... fixed now.
    Last edited by CtrlAltKick; 03-30-2002 at 09:29 AM.

  13. #13
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    I was just showing him the way how to display the numbers. If you want to save them here's the way of doing it:

    Code:
    # include <stdio.h>
    # include <conio.h>
    
    int main()
    {
    	FILE *fin= NULL;
    	int i = 0, Numbers = 0, IntArray[100];
    
    	fin = fopen("numbers.txt", "rt");
    
    	while (fscanf(fin, "%d", &Numbers) != EOF)
    	{
    		IntArray[i++] = Numbers;
    	}
    	getch();
    	return 0;
    }
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  14. #14
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    ok, thats pretty much the same thing i posted except i
    i used fgets, strtol, and getchar instead of fscanf and getch.

    you say you were showing him how to print out the numbers but his post wasnt asking for that. i still dont see how the efficiency of...

    Code:
    fscanf(file, "%d %*d %d %*d %d", &a, &b, &c);
    really matters in this case. i just answered his question. he wasnt asking how to print the numbers out or save them to an array of int.

  15. #15
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    you say you were showing him how to print out the numbers but his post wasnt asking for that.
    I know that but I just want to show him how to read numbers from a file and I didn't want to give him a direct solution.

    i still dont see how the efficiency of...
    Code:
    fscanf(file, "%d %*d %d %*d %d", &a, &b, &c);
    really matters in this case. i just answered his question
    And what about if you have 1000 of numbers in your file. What will you do?? Write 1000 variables for each number or you will be smart and saved them into an array of integers?
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