File IO

This is a discussion on File IO within the C Programming forums, part of the General Programming Boards category; I want to scan a text file: Code: jones,1,2,3,4 smith,2,3,4,5 john,57,65,4,2 catherine,25,64,78,65 I want ask a few questions: (1) Can ...

  1. #1
    Registered User mlsbbe's Avatar
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    File IO

    I want to scan a text file:
    Code:
    jones,1,2,3,4
    smith,2,3,4,5
    john,57,65,4,2
    catherine,25,64,78,65
    I want ask a few questions:
    (1) Can anybody give me any functions on how I can use to do this (or point me in the general direction).
    I tried using fscanf, but it keeps on giving me the wrong answers.
    Below is the code

    Code:
    #include <stdio.h>
    
    #define MAXSTUDENT 40
    #define MAXNAME 20
    
    typedef struct student_t{
    char name[(MAXNAME+1)];
    int exam1,exam2, exam3, exam4;
    float average;
    };
    
    int main(void)
    {                 
    FILE *readfile;
    int num=4;                            
    int check;
    student_t student[MAXSTUDENT] = {0};
    
    int i;
                                  
    if((readfile=fopen("datafile.txt","rt"))==NULL)
    {
    printf("Error, unable to read file.  Program exiting");
    return (1);
    }else
     {
     
    
     for(i=0,check=0;i<num;i++)
     {
     
        do
        {
        check=fscanf(readfile,"%s,%d,%d,%d,%d",&student[i].name,&student[i].exam1,&student[i].exam2,&student[i].exam3,&student[i].exam4);
        printf(".");                   
        }while(check==4);
        
        printf("*");
      }
    printf("\n%d",student[0].exam1);
    printf("\n%d",student[0].exam2);
    printf("\n%d",student[0].exam3);
    printf("\n%d",student[0].exam4);
    
    }
    
    return 0;
    }
    Thanks in advance.

  2. #2
    End Of Line Hammer's Avatar
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    >>while(check==4)
    fscanf() returns the numbers of items extracted, which will be 5 if all goes well, not 4.

    In the fscanf() call, this:
    >>&student[i].name
    should be
    >>student[i].name
    as name is a array, and therefore already a pointer.

    Other ways would be to use fgets() and load a line at a time into memory, then do the parsing manually. This will give you greater control, but is more effort.

    [edit]
    And you keep overwriting the same array element as you never increment i in the do/while loop.
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  3. #3
    Registered User mlsbbe's Avatar
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    still stuck

    I am still stuck. How would you tell fscanf to read a new line from the data and store it?
    I can't give it a value like EOF, since this would mean the end of the file, not a new line.

    Again, thanks in advance =).

  4. #4
    End Of Line Hammer's Avatar
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    Why do you want the newline?

    Anyway, try a %c.
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  5. #5
    Registered User mlsbbe's Avatar
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    Unhappy

    I've tried changing &student[i].name to student[i].name, but i still can't read the file. The compiler gives something like:
    "Data if 'int' supplied where pointer is required"

    Code:
    #include <stdio.h>
    
    #define MAXSTUDENT 40
    #define MAXNAME 20
    
    typedef struct student_t{
    char name[(MAXNAME+1)];
    int exam1,exam2, exam3, exam4;
    float average;
    };
    
    int main(void)
    {                 
    FILE *readfile;
    int num=4;                            
    int check; 
    int i=0;
    student_t student[MAXSTUDENT] = {0};
    
    
                                  
    if((readfile=fopen("datafile.txt","rt"))==NULL)
    {
    printf("Error, unable to read file.  Program exiting");
    return (1);
    }else
     {
     
    
    
    
       while((fscanf(readfile,"%s,%d,%d,%d,%d",student[i].name,student[i].exam1,student[i].exam2,student[i].exam3,student[i].exam4)!=EOF))
            {
            printf(".");                 
            i++;
            }
          
        
    
    
    printf("\n%d",student[0].exam1);
    printf("\n%d",student[0].exam2);
    printf("\n%d",student[0].exam3);
    printf("\n%d",student[0].exam4);
    
    }
    fclose(readfile);
    
    return 0;
    }

  6. #6
    End Of Line Hammer's Avatar
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    Code:
    typedef struct {
      char name[(MAXNAME+1)];
      int exam1,exam2, exam3, exam4;
      float average;
    }student_t;
    In the fscanf() line, all the ints need to have the & put back on them:
    >>&student[i].exam1
    only the name can go without.

    To help solve your puzzle, print out the name as well as the numbers:

    Code:
    printf("\n%s",student[0].name);
    printf("\n%d",student[0].exam1);
    printf("\n%d",student[0].exam2);
    printf("\n%d",student[0].exam3);
    printf("\n%d",student[0].exam4);
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  7. #7
    Registered User mlsbbe's Avatar
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    For some reason, fscanf seams to be only taking a whole line from the text file and storing it in the string member of the structure. But I want the line to be stored in seperately into different members in the structure. Below is my code:
    Code:
    #include <stdio.h>
    
    #define MAXSTUDENT 40
    #define MAXNAME 20
    
    typedef struct{
    char name[(MAXNAME+1)];
    int exam1,exam2, exam3, exam4;
    float average;
    }student_t;
    
    int main(void)
    {                 
    FILE *readfile;
                                
    student_t student [MAXSTUDENT]; 
    int i=0;
    
    
    
                                  
    if((readfile=fopen("datafile.txt","rt"))==NULL)
    {
    printf("Error, unable to read file.  Program exiting");
    return (1);
    }else
     {
     
    
    
    
       while((fscanf(readfile,"%s,%d,%d,%d,%d",student[i].name,&student[i].exam1,&student[i].exam2,&student[i].exam3,&student[i].exam4)!=EOF))
            {
            printf(".");                 
            ++i;
            }
          
        
    
    
    printf("\n%s",student[0].name);
    printf("\n%d",student[0].exam1);
    printf("\n%d",student[0].exam2);
    printf("\n%d",student[0].exam3);
    printf("\n%d",student[0].exam4);
    
    }
    fclose(readfile);
    
    return 0;
    }
    However for the print out i seem be getting something like this:
    Code:
    jones,1,2,3,4 //for student[0].name
    0                    //for student[0].exam1
    2011641991  //for student[0].exam2
    2                    //for student[0].exam3
    66                  //for student[0].exam4
    But I want it to be something like this:
    Code:
    jones             //for student[0].name
    1                    //for student[0].exam1
    2                    //for student[0].exam2
    3                    //for student[0].exam3
    4                    //for student[0].exam4
    Would somebody please help? I've been stuck on this for hours. =(

    Thanks.

  8. #8
    Registered User Vber's Avatar
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    Well, it's because he is getting everything as string, I suggest you in the file change it to something like this:
    Code:
    jones 1 2 3 4
    And not jones,1,2,3,4.

    Also in fscanf you don't need those ',' just use it as:
    Code:
    fscanf(readfile,"%s%d%d%d%d",student[i].name,&student[i].exam1,&student[i].exam2,&student[i].exam3,&student[i].exam4)

  9. #9
    Registered User mlsbbe's Avatar
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    Unhappy yes

    Yes, i know that placing spaces in between would make it easier. But i want to know why it doesn't work it I use the comma operator?

    If it does, how can I make fscanf read the line of text?

  10. #10
    Just Lurking Dave_Sinkula's Avatar
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    >But i want to know why it doesn't work it I use the comma operator?
    The %s specifier is whitespace-delimited. You could use the %[ specifier instead.
    Code:
    /* test.txt
    jones,1,2,3,4
    smith,2,3,4,5
    john,57,65,4,2
    catherine,25,64,78,65
    */
    #include <stdlib.h>
    #include <stdio.h>
    
    #define MAXNAME 20
    
    struct student
    {
        char name[(MAXNAME+1)];
        int exam1,exam2, exam3, exam4;
        float average;
    };
    
    int main(void)
    {
        const char filename[] = "test.txt";
        FILE *file = fopen(filename, "r");
        if ( file != NULL )
        {
            struct student s;
            while ( fscanf(file, "%[^,],%d,%d,%d,%d", s.name,
                           &s.exam1, &s.exam2, &s.exam3, &s.exam4) == 5 )
            {
                s.average = (s.exam1 + s.exam2 + s.exam3 + s.exam4) / 4.0f;
                printf("%s: average = %f\n", s.name, s.average);
                while(fgetc(file) != '\n');
            }
            fclose(file);
        }
        return 0;
    }
    
    /* my output
    jones: average = 2.500000
    smith: average = 3.500000
    john: average = 32.000000
    catherine: average = 58.000000
    */
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  11. #11
    Registered User mlsbbe's Avatar
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    Unhappy Code doesn't work

    I tried your code on my compiler, but it doesn't work.

  12. #12
    Just Lurking Dave_Sinkula's Avatar
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    >I tried your code on my compiler, but it doesn't work.
    How to Report Bugs Effectively

    The example I posted used "test.txt", not "datafile.txt". Could this be why it doesn't work? Point taken, however: error messages in the code might have been helpful.

    In your code, does the replacing %s with %[^,] work like you want?
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  13. #13
    Registered User mlsbbe's Avatar
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    Smile Woops..sorry

    I tried it on my computer at home and now it works. Thanks very much! =)

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