为什么在二进制模式下不读取文件时seekg（）工作不正确？

Question

我有一个名为“ Sample.dat ”的文件，其中包含以下内容：

This is line 1
This is line 2
This is line 3
This is line 4

当我尝试使用std::ifstream::binary模式读取 WITHOUT 文件时，输出错误。代码：

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>

int main()
{
    std::ifstream inf("F:\\cpp_programming\\File_Input_Output\\Sample.dat");

    if(!inf)
    {
        std::cerr << "Uh oh, Sample.dat could not be opened!" << std::endl;
        exit(1);
    }

    std::string str1;
    inf.seekg(5);
    std::getline(inf, str1);
    std::cout << str1 << std::endl;

    inf.seekg(8, std::ios::cur);
    std::getline(inf, str1);
    std::cout << str1 << std::endl;

    inf.seekg(-15, std::ios::end);
    std::getline(inf, str1);
    std::cout << str1 << std::endl;

    return 0;
}

输出（不正确）是：

is line 1
e 2
his is line 4

使用std::ifstream::binary模式时输出正确。代码：

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>

int main()
{
    std::ifstream inf("F:\\cpp_programming\\File_Input_Output\\Sample.dat", std::ifstream::binary);

    if(!inf)
    {
        std::cerr << "Uh oh, Sample.dat could not be opened!" << std::endl;
        exit(1);
    }

    std::string str1;
    inf.seekg(5);
    std::getline(inf, str1);
    std::cout << str1 << std::endl;

    inf.seekg(8, std::ios::cur);
    std::getline(inf, str1);
    std::cout << str1 << std::endl;

    inf.seekg(-15, std::ios::end);
    std::getline(inf, str1);
    std::cout << str1 << std::endl;

    return 0;
}

输出（正确）是：

is line 1
line 2
his is line 4

为什么二进制模式会给出正确的输出？