同时读取和写入文件？

问题描述

在此处移动了问题。假设，我想存储1,000,000,000整数，不能使用我的记忆。我会使用一个文件（它可以轻松处理这么多的数据）。
我如何让它读写的同时。
使用 fstream文件（file.txt，ios :: out | ios :: in）; 首先不创建文件。
我的意思是这样：
让文件的内容为 111111
然后，如果我运行： -

Moved the question here. Suppose, I want to store 1,000,000,000 integers and cannot use my memory. I would use a file(which can easily handle so much data ).How can I let it read and write and the same time.Using fstream file("file.txt', ios::out | ios::in ); doesn't create a file, in the first place. But supposing the file exists, I am unable to use to do reading and writing simultaneously.WHat I mean is this :Let the contents of the file be 111111Then if I run : -

#include <fstream>
#include <iostream>
using namespace std;
int main()
{
  fstream file("file.txt",ios:in|ios::out);
  char x;
  while( file>>x)
  {
    file<<'0';
  }
 return 0;
}

文件的内容不应为 101010 ？读取一个字符然后用0覆盖下一个字符或者将整个内容立即读入某个缓冲区，应该在文件中没有至少一个0？ 1111110 ？
但是内容保持不变，请解释。
谢谢。

Shouldn't the file's contents now be 101010 ? Read one character and then overwrite the next one with 0 ? Or incase the entire contents were read at once into some buffer, should there not be atleast one 0 in the file ? 1111110 ?But the contents remain unaltered. Please explain.Thank you.

推荐答案

保持两个指针，一个读和一个写。如果您正在进行读/写操作，则需要使用 seeg 和 seekp 成员函数显式设置这些指针。你还会发现，做格式化的I / O可能会干扰你想要做的事情，所以你应该使用 get / put 和读取 / 写入。

The filestreams maintain two pointers, one of reading and one for writing. If you are doing read/write operations you need to set these pointers explicitly with the seeg and seekp member functions. You will also find that doing formatted I/O may interfere with what you are trying to do, so you should be using the get/put and read/write member functions instead.

另请参见了解有关fstreams开放模式的更多信息。

See also http://stackoverflow.com/questions/2305480/why-cant-i-read-and-append-with-stdfstream-on-mac-os-x for more on open modes with fstreams.

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