First node reassigned new data is read in

Question

I have created a linked list, now I am trying to read data in from a file however every time a new entry is read and assigned to the structure the first node is reassigned and removes the data from the previous entry. I would like to find out why my code is doing this.

/* read file containing database of employees */
static void read_employee_database(char *file_name)
{
    char Name[MAX_NAME_LENGTH] = "\0";
    int Age;
    char Sex;
    char Job[MAX_JOB_LENGTH] = "\0";
    char ptr[10];
    char temp[100];
    int test = 0, count = 0;
    /*assigns enough memory*/
    Employee *pNewStruct = (Employee *)malloc(sizeof(Employee));



    FILE *pFile;    

    pFile = fopen(file_name, "r");
    while (feof(pFile) == 0) {
        fprintf(stderr, "\nFirst node name %s\n\n", pFirstNode->name);


        read_string(pFile, "Name: ", Name, MAX_NAME_LENGTH);
        strcpy(pNewStruct->name, Name);
        read_string(pFile, "Sex: ", temp, 4);
        Sex = temp[0];
        pNewStruct->sex = Sex;
        read_string(pFile, "Age: ", temp, 100);
        Age = atoi(temp);
        pNewStruct->age = Age;
        read_string(pFile, "Job: ", Job, MAX_JOB_LENGTH);
        strcpy(pNewStruct->job, Job);

        fprintf(stderr, "The name is: %s \n", Name);
        fprintf(stderr, "The Age is: %i \n", Age);
        fprintf(stderr, "The Sex is: %c \n", Sex);
        fprintf(stderr, "The Job is: %s \n", Job);
        fprintf(stderr, "\n");

        fgetc(pFile);
        /*Test all data for given entry*/
        test = checkName(&pNewStruct->name);
        if (test == 0) {
            fprintf(stderr, "Name is issue");
            exit(-1);
        }
        else if (pNewStruct->sex != 'M' && pNewStruct->sex != 'F') {
            fprintf(stderr, "Sex is issue");
            exit(-1);
        }
        else if (pNewStruct->age <= 0) {
            fprintf(stderr, "Age is issue");
            exit(-1);
        }
        else if (strlen(pNewStruct->job) == 0) {
            fprintf(stderr, "Job is issue");
            exit(-1);
        }
        else {

            if (pFirstNode->name == NULL) {
                fprintf(stderr, "a new node is created\n\n");
                pNewStruct->next = NULL;
                pNewStruct->prev = NULL;
                pFirstNode = pNewStruct;
            }
            else {
                fprintf(stderr, "Else statement run\n\n");
            }
        }
    }

    fclose(pFile);
}

At this point in the code I only expect that the first node will be assigned given "pFirstNode" is a public variable that is NULL. However the newest entry that is read in automatically is set as pFirstNode even though the if statement condition is not met.

The Actual output:


First node name (null)

The name is: Graham, Billy
The Age is: 63
The Sex is: M
The Job is: Evangelist

a new node is created


First node name Graham, Billy

The name is: Karula, Roger
The Age is: 23
The Sex is: M
The Job is: Engineer

Else statement run


First node name Karula, Roger

The name is: Smart, Lisa
The Age is: 18
The Sex is: F
The Job is: Trainee engineer

Else statement run

I am using Ubuntu if that is important.

Read [**Why is “while (!feof(file))” always wrong?**](https://stackoverflow.com/questions/5431941/why-is-while-feoffile-always-wrong) — Andrew Henle, Apr 03 '19 at 10:49

bruno · Accepted Answer · 2019-04-03T11:09:03.483

First node reassigned new data is read in

you allocate only one Employee, so you rewrite all the time in it, you need a to allocate one for each cell

Employee *pNewStruct = (Employee *)malloc(sizeof(Employee));

must be moved in the while, for instance just after

read_string(pFile, "Name: ", Name, MAX_NAME_LENGTH);

You will add the cells at the end of the list to respect the order, for that add a var pointing to the last cell (e.g. pLastCell)

In

       if (pFirstNode->name == NULL) {
           fprintf(stderr, "a new node is created\n\n");
           pNewStruct->next = NULL;
           pNewStruct->prev = NULL;
           pFirstNode = pNewStruct;
       }

add pLastCell = pNewStruct;

In

        else {
           fprintf(stderr, "Else statement run\n\n");
       }

you need to link the other cells :

  pLastCell->next = pNewStruct;
  pNewStruct->prev = pLastCell;
  pLastCell = pNewStruct;
  pNewStruct->next = NULL;

Do not use feof, detect the end of the file in read_string, also manage the case where the file is invalid and some fields are missing

For instance :

while (read_string(pFile, "Name: ", Name, MAX_NAME_LENGTH))

and read_string returns 0 on EOF/error

Remove fprintf(stderr, "\nFirst node name %s\n\n", pFirstNode->name); it has no sense

First node reassigned new data is read in

1 Answers1