C ++：获取不正确的文件大小 [英] C++: Getting incorrect file size

问题描述

我使用的是Linux和C ++。我有一个大小为210732字节的二进制文件，但是与seekg / tellg报告的大小是210728。

I'm using Linux and C++. I have a binary file with a size of 210732 bytes, but the size reported with seekg/tellg is 210728.

我从ls-la获得以下信息， 210732个字节：

I get the following information from ls-la, i.e., 210732 bytes:

-rw-rw-r-- 1 pjs pjs 210732 Feb 17 10:25 output.osr

-rw-rw-r-- 1 pjs pjs 210732 Feb 17 10:25 output.osr

使用下面的代码片段，我得到210728：

And with the following code snippet, I get 210728:

std::ifstream handle;
handle.open("output.osr", std::ios::binary | std::ios::in);
handle.seekg(0, std::ios::end);
std::cout << "file size:" << static_cast<unsigned int>(handle.tellg()) << std::endl;

所以我的代码关闭了4个字节。我已经确认文件的大小是正确的十六进制编辑器。那么为什么我得不到正确的大小？

So my code is off by 4 bytes. I have confirmed that the size of the file is correct with a hex editor. So why am I not getting the correct size?

我的回答：我认为这个问题是由于有多个打开fstreams的文件。至少，似乎已经整理出来了我。感谢所有帮助过的人。

推荐答案

至少对于64位CentOS 5上的G ++ 4.1和4.4 ，下面的代码按预期工作，即程序打印输出的长度与stat（）调用返回的长度相同。

At least for me with G++ 4.1 and 4.4 on 64-bit CentOS 5, the code below works as expected, i.e. the length the program prints out is the same as that returned by the stat() call.

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

int main () {
  int length;

  ifstream is;
  is.open ("test.txt", ios::binary | std::ios::in);

  // get length of file:
  is.seekg (0, ios::end);
  length = is.tellg();
  is.seekg (0, ios::beg);

  cout << "Length: " << length << "\nThe following should be zero: " 
       << is.tellg() << "\n";

  return 0;
}

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