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

void load_n_work(char *name, char *substr, int pos);


int main(int argc, char *argv[]) {
    /*if (argc < 3) { printf("Not enought arguments\n"); system("pause"); exit(1); }
    char *name = (char *)argv[1];
    char *substr = (char *)argv[2];
    int num = atoi(argv[3]);*/

    char *name = "name.txt";
    char *substr = "(test)";
    int pos = (atoi("5")-1); //позиция в файле для смещения
    load_n_work(name, substr, pos);
    system("pause");

}

void load_n_work(char * name, char * substr, int pos)
{
    FILE *fp;
    if ((fp = fopen(name, "r+")) == NULL) { printf("error\n"); exit(1); }
    int space = strlen(substr);
    fseek(fp, -1, SEEK_END); //qwert|y
    char ch;
    int test = ftell(fp);
    printf("In the beginning, pointer is on %d position\n", test);
    int flag = 0;

    while (!flag) {


        if (ftell(fp) == pos) flag = 1;
        ch = fgetc(fp);  //qwert(y)|
        test = ftell(fp);
        printf("After grabbing a char, pointer is on %d position\n", test);


        fseek(fp, space - 1, SEEK_CUR);     //(space = 5)    qwerty....|.
        fputc(ch, fp);                      //(space = 5)    qwerty....y|
        test = ftell(fp);
        printf("After releasing a char, pointer is on %d position\n", test);
        fseek(fp, -(space + 2), SEEK_CUR);  //(space = 5)    qwer|ty....y
        //system("pause");

    }
    fseek(fp, pos, SEEK_SET);
    fputs(substr, fp);

    fclose(fp);


}