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Using Linked List to write to a file

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Join Date: Apr 2009
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Using Linked List to write to a file

 
0
  #1
Apr 23rd, 2009
Hello,
I am having a problem. The task I have been given is to implement a queue using a linked list. One of the functions of the program is it accept input from the user and write this to a file. The program, thus far, accepts the information, but prints garbage to the .txt file. I would really appreciate any assistance offered. Thank you. A section of the program has been added.
C Syntax (Toggle Plain Text) 
  1. int main (void)
  2. {
  3.    FILE *jPtr;
  4.    JobPtr headPtr = NULL;
  5.    JobPtr tailPtr = NULL;
  6.    int choice;
  7.    int number;
  8.    char item;
  9.  
  10.   main_menu();
  11.  
  12.    while(choice!=4)
  13.    {
  14.       switch(choice)
  15.       {
  16.          case 1:
  17.          system("cls");
  18.          addFunction(&headPtr,&tailPtr);
  19.          main_menu();
  20.          scanf("%d", &choice);
  21.          break;
  22.  
  23.          case 2:
  24.          system("cls");
  25.          if(!isEmpty(headPtr))
  26.          {
  27.            item =  removeFunction(&headPtr, &tailPtr);
  28.            printf("Job has been removed from list.\n");
  29.          }
  30.          main_menu();
  31.          scanf("%d", &choice);
  32.          break;
  33.  
  34.          case 3:
  35.          system("cls");
  36.          displayFunction(headPtr);
  37.          main_menu();
  38.          scanf("%d", &choice);
  39.          break;
  40.  
  41.          default:
  42.          printf("Invalid choice.\n");
  43.          system("cls");
  44.          main_menu();
  45.          scanf("%d", &choice);
  46.          break;
  47.       }
  48.  
  49.    }
  50.    return 0;
  51. }
  52.  
  53. /******************************************************************************/
  54. /*                         addFunction                                        */
  55. /******************************************************************************/
  56.  
  57. void addFunction(JobPtr *headPtr, JobPtr *tailPtr)
  58. {
  59.  
  60.    FILE *jPtr;
  61.    int number;
  62.    JobPtr newPtr;    /*pointer to new node*/
  63.    newPtr = malloc(sizeof(job));       /*create new node*/
  64.    //struct jobData jobs = {0,"","","","","","",""};
  65.    if ((jPtr = fopen("jobticket.txt", "w"))== NULL)
  66.    {
  67.       printf("File could not be opened\n");
  68.    }
  69.    fclose (jPtr);
  70.    if ((jPtr = fopen("jobticket.txt", "rb+"))==NULL)
  71.    {
  72.        printf("File could not be opened\n");
  73.    } /*end if*/
  74.    else
  75.    {
  76.        while (fwrite(newPtr,1, sizeof(*newPtr),jPtr)>0)
  77.        {
  78.          printf("Enter jobnum: ");
  79.          scanf("%d",&number);
  80.           fflush(stdin);
  81.                if (number == 0)
  82.                break;
  83.  
  84.  
  85.           fseek(jPtr, (number-1)* sizeof(struct jobData), SEEK_SET);
  86.           fread(newPtr, sizeof(*newPtr),1,jPtr);
  87.  
  88.           newPtr->jobnum = number;
  89.  
  90.  
  91.           printf("Enter a brief description of problem: \n");
  92.           gets(newPtr->jissue);
  93.  
  94.  
  95.           printf("Enter worktype: \n");
  96.           gets(newPtr->wtype);
  97.  
  98.           printf("Enter date. Enter in this format DD/MM/YY: \n");
  99.           gets(newPtr->date);
  100.  
  101.           printf("Enter technician to which job will be assigned. "
  102.                   "(technician chosen according to work location): \n");
  103.           gets(newPtr->techcode);
  104.  
  105.           newPtr->nextPtr=NULL;
  106.  
  107.  
  108.            fwrite(newPtr,1,sizeof(struct jobData),jPtr); //fwrite(this, sizeof(*this), 1, fp);
  109.            // printf("%d",x);
  110.              //}
  111.           fseek(jPtr, (number-1)* sizeof(struct jobData), SEEK_SET);
  112.  
  113.  
  114.           if(isEmpty(*headPtr))
  115.           {
  116.              *headPtr = newPtr;
  117.           }
  118.           else
  119.           {
  120.              (*tailPtr)->nextPtr = newPtr;
  121.           }
  122.               *tailPtr = newPtr;
  123.         }
  124.         //else
  125.         //{
  126.        // /    printf("Information not inserted. No memory available.\n");
  127.        // }
  128.     }
  129.     fclose(jPtr);
  130.  
  131. }
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Re: Using Linked List to write to a file

 
0
  #2
Apr 23rd, 2009
Some points for now:
C Syntax (Toggle Plain Text) 
  1. newPtr = malloc(sizeof(job));       /*create new node*/
What's job? I don't see job anywhere.


c Syntax (Toggle Plain Text) 
  1.    if ((jPtr = fopen("jobticket.txt", "w"))== NULL)
  2.    {
  3.       printf("File could not be opened\n");
  4.    }
  5.    fclose (jPtr);
Doesn't make any sense regardless the file gets opened or not you close it right away. You can not close a file that's not opened.

> gets(newPtr->jissue); Forget you know there's a function named gets(). It is not good to use in any circumstance, because it will always overflow the buffer given the opportunity. fgets() is a very appropriated alternative
Last edited by Aia; Apr 23rd, 2009 at 11:44 pm.
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Re: Using Linked List to write to a file

 
0
  #3
Apr 24th, 2009
Thank you for your speedy reply. job is a variable of the struct jobData.
Sorry about the file section. It should have been commented out.
Thank you for the advice on fgets, I will research and start implementing it. I'll let you know what happens. Thanks again for your speedy reply.
C Syntax (Toggle Plain Text) 
  1. struct jobData 
  2. {
  3.    int jobnum;
  4.    char itemname[20];
  5.    char jstatus[10];
  6.    char wtype[10];
  7.    char date[10];
  8.    char techcode[10];
  9.    char jreport[225];
  10.    char jissue[225];
  11.    struct jobData *nextPtr;
  12. };
  13. typedef struct jobData job;
  14. typedef job *JobPtr;
Last edited by Ancient Dragon; Apr 24th, 2009 at 10:52 am. Reason: correct code tags [/code] not [\code]
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Re: Using Linked List to write to a file

 
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  #4
Apr 24th, 2009
Thank you again for your speedy reply. I realized that I had 'jobs' instead of job and made that change.

Thank you for the advice on fgets. I did some research and removed the 'gets' and 'scanf' statements.

Garbage is still being printed to the .txt file. However, it's 'improved garbage', (not sure if that makes sense but I can see more information than last time).
Thanks again for any assistance you can give.



I've included the struct.
C Syntax (Toggle Plain Text) 
  1. struct jobData 
  2. {
  3.    int jobnum;
  4.    char itemname[20];
  5.    char jstatus[10];
  6.    char wtype[10];
  7.    char date[10];
  8.    char techcode[10];
  9.    char jreport[225];
  10.    char jissue[225];
  11.    struct jobData *nextPtr;
  12. };
  13. typedef struct jobData job;
  14. typedef job *JobPtr;

and the modified code

C Syntax (Toggle Plain Text) 
  1. /******************************************************************************/
  2. /*                         addFunction                                        */
  3. /******************************************************************************/
  4.  
  5. void addFunction(JobPtr *headPtr, JobPtr *tailPtr)
  6. {
  7.  
  8.    struct jobData job = {0,"","","","","","",""};
  9.    FILE *jPtr;
  10.    char input[3];
  11.    int number;
  12.    JobPtr newPtr;    /*pointer to new node*/
  13.    newPtr = malloc(sizeof(job));       /*create new node*/
  14.  
  15.  
  16.    if ((jPtr = fopen("jobticket.txt", "rb+"))==NULL)
  17.    {
  18.        printf("File could not be opened\n");
  19.    } /*end if*/
  20.    else
  21.    {
  22.        while (fwrite(newPtr,1, sizeof(*newPtr),jPtr)>0)
  23.        {
  24.          fputs("Enter jobnum: ",stdout);
  25.          fflush(stdout);
  26.          if ( fgets(input, sizeof input, stdin) )
  27. 			{
  28. 			   if ( sscanf(input, "%d", &number) == 1 )
  29. 				{
  30. 				   if (number == 0)
  31.                break;
  32.  
  33. 				}
  34.  
  35. 		   }
  36.  
  37.  
  38.  
  39.           fseek(jPtr, (number-1)* sizeof(struct jobData), SEEK_SET);
  40.           fread(newPtr, sizeof(*newPtr),1,jPtr);
  41.  
  42.           newPtr->jobnum = number;
  43.  
  44.  
  45.           printf("Enter a brief description of problem: \n");
  46.           mygetline(newPtr->jissue,sizeof newPtr->jissue);
  47.  
  48.  
  49.           printf("Enter worktype: \n");
  50.           mygetline(newPtr->wtype,sizeof newPtr->wtype);
  51.  
  52.           printf("Enter date. Enter in this format DD/MM/YY: \n");
  53.           mygetline(newPtr->date,sizeof newPtr->date);
  54.  
  55.           printf("Enter technician to which job will be assigned. "
  56.                   "(technician chosen according to work location): \n");
  57.           mygetline(newPtr->techcode,sizeof newPtr->techcode);
  58.  
  59.           newPtr->nextPtr=NULL;
  60.  
  61.  
  62.           fwrite(newPtr,1,sizeof(struct jobData),jPtr); 
  63.  
  64.           fseek(jPtr, (number-1)* sizeof(struct jobData), SEEK_SET);
  65.  
  66.  
  67.           if(isEmpty(*headPtr))
  68.           {
  69.              *headPtr = newPtr;
  70.           }
  71.           else
  72.           {
  73.              (*tailPtr)->nextPtr = newPtr;
  74.           }
  75.               *tailPtr = newPtr;
  76.         }
  77.         //else
  78.         //{
  79.        // /    printf("Information not inserted. No memory available.\n");
  80.        // }
  81.     }
  82.     fclose(jPtr);
  83.  
  84. }

NB. I've learned so much from the tutorials on this website. Thank you. Keep up the good work.
Last edited by natureG; Apr 24th, 2009 at 7:14 am.
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