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

  struct fullname {
    char firstName[40];
    char lastName[10];
  } info;

  int main(void){
    FILE *fp;

    if((fp=fopen("test", "rb")) == NULL) {
      printf("Cannot open file.\n");
      exit(1);
    }

    int client_num = 10;

    /* find the proper structure */
    fseek(fp, client_num*sizeof(struct fullname), SEEK_SET);

    /* read the data into memory */
    fread(&info, sizeof(struct fullname), 1, fp);

    fclose(fp);
  }