The content of the elements of the structure array changes after a while

Question

  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <errno.h>
  #include <crypt.h>
  #include <ctype.h>
  #include <assert.h>

  struct user {
  char* username;
  char* name;
  char* saltandhash;
  char* state;
  };

 int main(int argc, char **argv)
 { 

   if ( argc != 3 ) /* argc should be 2 for correct execution */
  {
    printf("usage: %s passwd-path shadow-path", argv[0]);
    exit(EXIT_FAILURE);
  }

  char* passwd = argv[1];
  char* shadow = argv[2];

  //file reading variables for passwd and shadow files
  FILE* fp_shadow;
  FILE* fp_passwd;
  char* line_shadow = NULL;
  char* line_passwd = NULL;
  size_t len_shadow = 0;
  size_t len_passwd = 0;
  ssize_t read_shadow;
  ssize_t read_passwd;
  //file reading for dictionary
  FILE* fp_dict;
  char* line_dict = NULL;
  size_t len_dict = 0;
  ssize_t read_dict;
  const char* dict = "top250short.txt";

  fp_shadow = fopen(shadow, "r");
  if (fp_shadow == NULL)
    exit(EXIT_FAILURE);

  fp_passwd = fopen(passwd, "r");
  if(fp_passwd == NULL)
   exit(EXIT_FAILURE);

  int first_time = 1;
  int found = 0;
  int counter = 0;
  struct user users[8196];
  struct user u = {NULL, NULL, NULL, NULL};
  char salt[6];
  char* username = NULL;
  char* saltandhash = NULL; 
  char* name = NULL;

  while ((read_shadow = getline(&line_shadow, &len_shadow, fp_shadow)) != -1) {

    //Handle shadow file
    username = strdup(strsep(&line_shadow, ":"));
    saltandhash = strdup(strsep(&line_shadow, ":"));

    if(first_time){
     int i;
       for (i = 0; i < 6; ++i){
         salt[i] = saltandhash[i];
       }
      first_time = 0;
     }

    //handle passwd file
    read_passwd = getline(&line_passwd, &len_passwd, fp_passwd);
    if(read_passwd == -1)
      exit(EXIT_FAILURE);

    strsep(&line_passwd, ":");
    strsep(&line_passwd, ":");
    strsep(&line_passwd, ":");
    strsep(&line_passwd, ":");
    name = strdup(strsep(&line_passwd, ":"));

    u.username = strdup(username);
    u.name = strdup(name);
    u.saltandhash = strdup(saltandhash);
    u.state = strdup("NF"); //not found
    users[counter] = u;

    printf("%s***%s***%s\n", users[0].username, users[0].saltandhash, users[0].state);
    counter++;
 }
   return 0;
}

In this code, I am trying to read passwd and shadow from files and store the values ​​that I analyze in an array of structures.

The passwd file is as follows:

 mly460:x:1002:1002:Michael Lily,,,:/home/mly460:/bin/sh
 (and similar lines)

the shadow file is as follows:

 mly460:$1$R5$yo1/aN8VtX54qAf1W8Rhe0:16458::::::
 (and similar lines)

The output of this program at startup. / executable passwd-path shadow-path

mly460***$1$R5$yo1/aN8VtX54qAf1W8Rhe0***NF
mly460***$1$R5$yo1/aN8VtX54qAf1W8Rhe0***NF
mly460***$1$R5$yo1/aN8VtX54qAf1W8Rhe0***NF
tcsh
***$1$R5$yo1/aN8VtX54qAf1W8Rhe0***NF
***$1$R5$yo1/aN8VtX54qAf1W8Rhe0***NF
***59:/bin/tcsh
***NF
***011***NF
***011***Calvert,,,
***011***Calvert,,,
:::
***011***Calvert,,,
1$R5$Z8T2h9IbKpHEhVouZOXIt1***011***Calvert,,,
1$R5$Z8T2h9IbKpHEhVouZOXIt1***16415::::::
***Calvert,,,
1$R5$Z8T2h9IbKpHEhVouZOXIt1***bwm505***
1$R5$Z8T2h9IbKpHEhVouZOXIt1***bwm505***$kMLZJaGeDjfu0e3d5XZM/1
1$R5$Z8T2h9IbKpHEhVouZOXIt1***bwm505***$kMLZJaGeDjfu0e3d5XZM/1
1$R5$Z8T2h9IbKpHEhVouZOXIt1***bwm505***$kMLZJaGeDjfu0e3d5XZM/1
(and the rest is the same line.)

As you can see at the end, I always print the contents of the structure, which is stored at the 0th position in the users array.

What is strange is that the contents of the 0-th CHANGE element as a while loop progresses, but after a certain point it stabilizes to a certain value.

. "saltandhash", , printf. ( , .)

- ?

( ): strsep line_shadow line_paswd. char * , :

char* copy_to_parse = strdup(line_shadow);