/*********************************************************************************************
    Description: Get specific line of a txt file

    Copyright : All right reserved by NCIC.ICT

    Author : Zhang Zhonghai
    Date : 2023/08/28
***********************************************************************************************/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define READ_BUF_SIZE 102400000

int main(int argc, char *argv[])
{
    if (argc < 3)
    {
        fprintf(stderr, "Please input the file path and the line number you want to get!\n");
        return 1;
    }
    const char *in_path = argv[1];
    size_t expect_line_num = atoi(argv[2]);
    FILE *in_f = fopen(in_path, "r");
    char *read_buf = (char *)malloc(READ_BUF_SIZE);

    int actual_size = 0;
    int expect_size = READ_BUF_SIZE;
    size_t cur_line_num = 0;
    size_t last_line_pos = 0;
    size_t cur_line_pos = 0;
    int i, j;
    int flag_found = 0;
    // 读取数据
    actual_size = fread(read_buf, 1, expect_size, in_f);
    while (actual_size > 0)
    {
        for (i = 0; i < actual_size; ++i)
            if (read_buf[i] == '\n')
            {
                cur_line_num += 1;
                last_line_pos = cur_line_pos;
                cur_line_pos = i;
                if (cur_line_num == expect_line_num)
                {
                    for (j = last_line_pos + 1; j <= cur_line_pos; ++j)
                    {
                        fprintf(stdout, "%c", read_buf[j]);
                    }
                    flag_found = 1;
                    break;
                }
            }
        if (flag_found)
            break;
        actual_size = fread(read_buf, 1, expect_size, in_f);
    }
    if (!flag_found)
        fprintf(stderr, "Invalid line number!\n");
    return 0;
}