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error on reading data from file to sturct

Posted on 1998-10-07
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Last Modified: 2010-04-15
/*

     PROGRAM SORT VERSION BETA

*/
#include<stdio.h>
#include<stdlib.h>
#include<io.h>
#include<string.h>
#include<fcntl.h>


#include<conio.h>


#define DATASIZE 54
#define MARK 8
#define SPACE 8
#define HVALUE 7
#define DATE 14
#define SPACE2 4
#define TYPE 3
#define CR_LF 2

int main(int argc,char *argv[])
{
    FILE *fr,*fw;

    struct R_data{                         //struct of raw data
            struct R_data *before;
            char mark[MARK];
            char space1[SPACE];
            char H_value[HVALUE];
            char space2[SPACE];
            char date[DATE];
            char space3[SPACE2];
            char type[TYPE];
            char cr_lf[CR_LF];
            struct R_data *next;
            };

    struct R_data *Head,*Point,*Tail,*Phead,*Ptail;

/*------------------------------------------------------------------------*/

    if((fr = fopen(argv[argc-1],"r+t")) == NULL)
    {
       fprintf(stderr,"Cannot open input file.\n");
       return(1);
    }
    else
    {
       //initialize header of struct
       Head  = (struct R_data *)malloc(sizeof(struct R_data));
       Phead = Head;
       Head->before = NULL;
       Head->next   = NULL;
       while(feof(fr) == 0)
       {
        Point = (struct R_data *)malloc(sizeof(struct R_data));
        Phead->next = Point;
        Point->before = Phead;
        Phead = Phead->next;
        Phead->next = NULL;
        fread(Phead->mark,MARK,1,fr);
        fread(Phead->space1,SPACE,1,fr);
        fread(Phead->H_value,HVALUE,1,fr);
        fread(Phead->space2,SPACE,1,fr);
        fread(Phead->date,DATE,1,fr);
        fread(Phead->space3,SPACE2,1,fr);
        fread(Phead->type,TYPE,1,fr);
        fread(Phead->cr_lf,CR_LF,1,fr);

       }
       Point = (struct R_data *)malloc(sizeof(struct R_data));
       Phead->next = Point;
       Point->before = Phead;
       Point->next = NULL;
       Tail = Point;
       /*test*/

       Point = Head->next;
       while(Point != Tail)
       {
        printf("\n %s",Point->date);
        Point = Point->next;
        getch();
       }
       Point = Head;
       Phead = Head->next;
       while(Point <= Tail)
       {
       free(Point);
       Point = Phead;
       Phead = Phead->next;
       }

       /*test*/
       fclose(fr);
       return(0);
    }
}


******************************************************************************************************************************
Data characteristic
########        + 0.123        19980929145856    BSC
########        + 0.123        19980929145841    BSC
########        + 0.123        19980929145836    BSC


 Above is my program , use to read data from file that have characteris above and fill to struct for make link list.But problem is when I print the test result by " printf("\n %s",Point->date);  "  command.The result should be 1998... but the appearance is "19980929145856    BSC  " and follow by the character that can't read.
  Where the wrong in my program and how can I correct ?.
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Question by:dissathep
  • 4
  • 4
9 Comments
 
LVL 5

Accepted Solution

by:
scrapdog earned 70 total points
ID: 1253415
Your problem is that you are printing a string, and a NULL must be present to terminate the string.

When you read in the date, you are reading 14 characters from the file.  The array size is 14.  Since the last character in the array is 14, you array is full.  There's no room for the NULL.  Printf keeps printing all contiguous bytes until a NULL is found, it doesn't care what the size of your array is.

My suggestion is to define the length of each of the fields you are reading to one greater.

For example:

   char date[DATE];

should be changed to

   char date[DATE+1];

and so on.

This 15th character will leave room for the NULL when it comes time to print it out.  However, you will have to insert the NULL manually after you read the string from disk.

Like this:

fread(Phead->date,DATE,1,fr);
Phead->date[DATE] = NULL;

This will insert the NULL right into the data structure between the date and the space.  When you printf the date, all you will see is the fourteen characters of the date.

The same would go for any members of your data structure that you would want to print as a string.


---------------------------------------------------------
Of course, if you didn't want to do it this way (change the data structure), you could print the characters one at a time:

for(i=0;i<=(DATE-1);i++) printf("%c",date[i]);



scrapdog
0
 

Author Comment

by:dissathep
ID: 1253416
After read data from file to fill in sturct ,I will sort this data by date and write it back to a new file .Following write back finish I 'll take a new file to calculate again.So I don't want to change data from the original.Do you have any suggestion to correct correct my program?.
                                                                                  Thank a lot.
0
 

Author Comment

by:dissathep
ID: 1253417
After read data from file to fill in sturct ,I will sort this data by date and write it back to a new file .Following write back finish I 'll take a new file to calculate again.So I don't want to change data from the original.Do you have any suggestion to correct correct my program?.
                                                                                  Thank a lot.
0
 
LVL 5

Expert Comment

by:scrapdog
ID: 1253418
Even if you change your struct, you won't necessarily be changing the data.

Be inserting a NULL between the data and the space, it will be much easier to sort, because you can handle the date as a string, and pass it to strcmp, or whatever you will use.

When you write the file back to disk, you don't have to write the extra character.  All you have to do is fwrite it back the exact way you fread it.  Then the null won't be included in the file.

Example, if you fread it like this:

fread(Phead->date,DATE,1,fr);

then fwrite it like this:

fwrite(Phead->date,DATE,1,fw);  {or whatever you use for a stream}

This will write to disk exactly as you found it.  The extra array element for NULL would only exist in *memory*, for the purpose of manipulating it as a string.


On disk before fread:
............       (14 chars)
19980929145856

In memory after fread and insert a NULL
.............
19980929145856N    (where N is NULL)

You will write back only 14 chars of this (what was read), so

On disk after fwrite
............
19980929145856


The ONLY change that you have to make is

char date[DATE+1]

and then insert the null in date[DATE]

As long as you fwrite the same amount you fread, nothing will change.
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Author Comment

by:dissathep
ID: 1253419
The suggestion not work.It has the same result.Do you have any suggestion?.
0
 
LVL 5

Expert Comment

by:scrapdog
ID: 1253420
If you post the source code that includes my suggestion I could try to see what'ss wrong.
0
 

Author Comment

by:dissathep
ID: 1253421
/*

     PROGRAM SORT VERSION BETA

*/
#include<stdio.h>
#include<stdlib.h>
#include<io.h>
#include<string.h>
#include<fcntl.h>


#include<conio.h>


#define DATASIZE 54
#define MARK 8
#define SPACE 8
#define HVALUE 7
#define DATE 14
#define SPACE2 4
#define TYPE 3
#define CR_LF 2

int main(int argc,char *argv[])
{
    FILE *fr,*fw;

    struct R_data{                         //struct of raw data
            struct R_data *before;
            char mark[MARK+1];
            char space1[SPACE+1];
            char H_value[HVALUE+1];
            char space2[SPACE+1];
            char date[DATE+1];
            char space3[SPACE2+1];
            char type[TYPE+1];
            char cr_lf[CR_LF+1];
            struct R_data *next;
            };

    struct R_data *Head,*Point,*Tail,*Phead,*Ptail;

/*------------------------------------------------------------------------*/

    if((fr = fopen(argv[argc-1],"r+t")) == NULL)
    {
       fprintf(stderr,"Cannot open input file.\n");
       return(1);
    }
    else
    {
       //initialize header of struct
       Head  = (struct R_data *)malloc(sizeof(struct R_data));
       Phead = Head;
       Head->before = NULL;
       Head->next   = NULL;
       while(feof(fr) == 0)
       {
        Point = (struct R_data *)malloc(sizeof(struct R_data));
        Phead->next = Point;
        Point->before = Phead;
        Phead = Phead->next;
        Phead->next = NULL;

        Phead->mark[MARK] = NULL;
        Phead->space1[SPACE] = NULL;
        Phead->H_value[HVALUE] = NULL;
        Phead->space2[SPACE] = NULL;
        Phead->date[DATE] = NULL;
        Phead->space3[SPACE2] = NULL;
        Phead->type[TYPE] = NULL;
        Phead->cr_lf[CR_LF] = NULL;

        fread(Phead->mark,MARK,1,fr);
        fread(Phead->space1,SPACE,1,fr);
        fread(Phead->H_value,HVALUE,1,fr);
        fread(Phead->space2,SPACE,1,fr);
        fread(Phead->date,DATE,1,fr);
        fread(Phead->space3,SPACE2,1,fr);
        fread(Phead->type,TYPE,1,fr);
        fread(Phead->cr_lf,CR_LF,1,fr);

        

       }
       Point = (struct R_data *)malloc(sizeof(struct R_data));
       Phead->next = Point;
       Point->before = Phead;
       Point->next = NULL;
       Tail = Point;
       /*test*/

       Point = Head->next;
       while(Point != Tail)
       {
        int i;
        printf("%s\n",Point->date);
        Point = Point->next;
        getch();
       }
       Point = Head;
       Phead = Head->next;
       while(Point <= Tail)
       {
       free(Point);
       Point = Phead;
       Phead = Phead->next;
       }

       /*test*/
       fclose(fr);
       return(0);
    }
}


This 's the source after correct.Pls tell me the code of Carriage-Return and End-of-File used within"strcmp()"command . I 'm not sure that use "\r" ,"\n","\0".
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LVL 5

Expert Comment

by:scrapdog
ID: 1253422
Try setting the nulls AFTER you read the file.

Like this

fread(Phead->mark,MARK,1,fr);
  fread(Phead->space1,SPACE,1,fr);
  fread(Phead->H_value,HVALUE,1,fr);
  fread(Phead->space2,SPACE,1,fr);
  fread(Phead->date,DATE,1,fr);
  fread(Phead->space3,SPACE2,1,fr);
  fread(Phead->type,TYPE,1,fr);
  fread(Phead->cr_lf,CR_LF,1,fr);
  Phead->mark[MARK] = NULL;
  Phead->space1[SPACE] = NULL;
  Phead->H_value[HVALUE] = NULL;
  Phead->space2[SPACE] = NULL;
  Phead->date[DATE] = NULL;
  Phead->space3[SPACE2] = NULL;
  Phead->type[TYPE] = NULL;
  Phead->cr_lf[CR_LF] = NULL;

See if this works.

\0 tells strcmp that the end of the string has been reached.

\n and \r are the same thing (i think).  Both of these represent ASCII #13, the carriage return.  

(I am not sure but) I don't think \n and \r affect strcmp.  \0 (NULL) does though.


0
 
LVL 16

Expert Comment

by:imladris
ID: 1253423
\n an \r do not affect strcmp, however they are not the same. \n represents a newline or linefeed and is encoded 0x0a. \r is a carriage return: 0x0d.

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