c++ - wifstream.tellg() 在流中的前进位置？

Question

我一直在 Visual Studio 2015 中使用 iostream 进行一些基本的文件操作，并注意到这种奇怪的行为。

#include <fstream>
#include <iostream>
#include <sstream>

void main(int argc, char** argv)
{
    std::wifstream stream("example.txt");
    //std::ifstream stream("example.txt");
    //std::wstringstream stream(L"abcdefghijklmnopqrstuvxyz");

    std::wcout << (char)stream.peek() << "\n"; // a
    stream.tellg();
    std::wcout << (char)stream.peek() << "\n"; // b
    stream.tellg();
    std::wcout << (char)stream.peek() << "\n"; // c
    stream.tellg();
    std::wcout << (char)stream.peek() << "\n"; // d
    stream.tellg();
    std::wcout << (char)stream.peek() << "\n"; // e
    stream.tellg();
    std::wcout << (char)stream.peek() << "\n"; // f
    stream.tellg();
    std::wcout << (char)stream.peek() << "\n"; // g
    stream.tellg();
}

example.txt 包含:

abcdefghijklmnopqrstuvxyz

似乎 stream.tellg() 将流的当前字符前进了一个。这仅发生在 std::wifstream 中。 std::ifstream 和 std::wstringstream 似乎没有受到影响。

这是 visual studio STL 实现中的错误吗？

Answer 1

此问题与 wifstream/wfstream implementation bug in Visual C++ 2010 类似.

正如斯蒂芬所说:

C++ Standard does not provide behavior guarantees when calling tellg() on a file opened in text mode.

我想这就是原因。