C++：file.seekg() 似乎没有返回当前位置

Question

我正在尝试备份 ifstream 中的一行。 file.tellg() 正在返回一个我没想到的值。在下面的示例中，在读取第一行（长度为 15 个字符的字符串）后，我希望 file.tellg() 返回 16。相反，它返回 41。有人可以提供一些关于这种行为的见解吗？

test.cpp

#include <fstream>
#include <ios>
#include <string>
#include <iostream>
using namespace std;

int main(){
    ifstream file("sample.ics", ios::in);

    string line;
    string key0;
    string key1;
    string value0;
    string value1;

    getline(file, line, '\n');

    cout << "line = " << line << endl;
    cout << "line.length = " << line.length() << endl; // should be 15;

    cout << "Attempt:" << endl;
    int pos = file.tellg(); // should be 16;
    cout << "  pos = " << pos << endl;

    getline(file, key0, ':');
    getline(file, value0, '\n');

    cout << "  First:" << endl;
    cout << "    " << key0 << ":" << value0 << endl;

    cout << "  backing up..." << endl;
    file.seekg(pos, ios_base::beg);

    getline(file, key1, ':');
    getline(file, value1, '\n');

    cout << "  Second:" << endl;
    cout << "    " << key1 << ":" << value1 << endl;

    file.close();
}

输出：

line = BEGIN:VCALENDAR
line.length = 15
Attempt:
  pos = 41
  First:
    CALSCALE:GREGORIAN
  backing up...
  Second:
    ION:2.0

sample.ics

BEGIN:VCALENDAR
CALSCALE:GREGORIAN
VERSION:2.0
METHOD:PUBLISH
...

Answer 1

尝试以二进制模式打开文件，看看是否得到相同的结果：

ifstream 文件("sample.ics", ios::binary);