Code is adding extra characters

Question

I have a function that is supposed to read through a file, put the individual lines, as separate elements, into an array. Then it's supposed to go through the array and put certain elements at certain positions within the struct.

I almost have it... When I go to print the struct to make sure it's getting everything right, extra characters are showing up!

This is what is in the file:

123
pre
45
cse
67
345
ret
45
cse
56

And this is what it's printing:

123
pre
45
cse
C
67
345
ret
45
cse
8
56

Here is the code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct students         //Defining structure for students
{
    int id;        //Students ID Number
    char name[30];      //Students Name
    int age;            //Students Age
    char dept[4];       //Studets Department
    int grade;          //Students Grade
};



int main()
{
    struct students list[20];
    FILE *f;
    char line[30];
    char **temp = NULL;
    int num_righ = 0;
    int id5;
    int age5;
    int grade5;
    int i, k;

    f = fopen("records.txt", "r");



    while(fgets(line, sizeof (line), f) != NULL)
    {
        if (line != NULL)
        {
            num_righ++;
            temp = (char**)realloc(temp, sizeof(char*) *num_righ);
            temp[num_righ - 1] = strdup(line);
        }
    }

    fclose(f);
    k = 0;
    i = 0;
    while (temp[i] != NULL)
    {
        id5 = atoi(temp[i]);
        list[k].id = id5;
        i++;
        strcpy(list[k].name, temp[i]);
        i++;
        age5 = atoi(temp[i]);
        list[k].age = age5;
        i++;
        strcpy(list[k].dept, temp[i]);
        i++;
        grade5 = atoi(temp[i]);
        list[k].grade = grade5;
        i++;
        k++;


    }
    for (i = 0; i < k; i++)
    {
        printf("%d\n", list[i].id);
        printf("%s", list[i].name);
        printf("%d\n", list[i].age);
        printf("%s\n", list[i].dept);
        printf("%d\n", list[i].grade);
    }
}

Answer 1

One thing to note is that the decimal value for 'C' is 67, and the decimal value for '8' is 56. Your dept array in your students array is too small. It is grabbing the newline character, and is then unable to store a terminating character. The printf runs through to the grade integer, which is printed as a char.

EDIT: Rather, your array isn't too small, but fgets is grabbing the newline, which fills the array, preventing the null terminator from being stored properly.

Answer 2

The following code addresses multiple problems - not only does it make sure that strings are "safely" copied (using strncpy, and terminating the string with a '\0'), but it also makes sure you don't create a second copy of all the data in memory (not a problem with a toy example, but why start with bad habits).

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct students         //Defining structure for students
{
    int id;        //Students ID Number
    char name[30];      //Students Name
    int age;            //Students Age
    char dept[4];       //Studets Department
    int grade;          //Students Grade
};

int main()
{
    struct students list[20];
    FILE *f;
    char line[30];
    char **temp = NULL;
    int num_righ = 0;
    int id5;
    int age5;
    int grade5;
    int i, k=0;
    char *newLine;

    f = fopen("records.txt", "r");
    int s = 0;  // this is the "state" counter - it goes from 0 to 4, then back to 0

    while(fgets(line, sizeof (line), f) != NULL)
    {
       newLine = strchr(line, '\n');
       if(newLine) *newLine='\0'; // terminate string on the newline.
        switch(s) {
          case 0:
            list[k].id = atoi(line);
            break;
          case 1:
             strncpy(list[k].name, line, 30);
             list[k].name[29]='\0'; // make sure it is terminated
             break;
          case 2:
            list[k].age = atoi(line);
            break;
          case 3:
            strncpy(list[k].dept, line, 3);
            list[k].dept[3] = '\0'; // make sure it is terminated
            break;
          case 4:
            list[k].grade = atoi(line);
            break;
        }
        s++;
        if (s == 5) {
          s = 0;
          k++; // if it's 5, go back to zero and start reading next structure
        }
      }
    fclose(f);

    for (i = 0; i < k; i++)
    {
        printf("id: %d\n", list[i].id);
        printf("name: %s", list[i].name);
        printf("age: %d\n", list[i].age);
        printf("dept: %s\n", list[i].dept);
        printf("grade: %d\n\n", list[i].grade);
    }
}