使用fstream打开文件后如何清除文件内容？ [英] How to clear the content of a file after it is opened using fstream?

问题描述

我需要以读写模式打开文件，读取文件内容，然后清除所有文件。因此，我无法在截断模式下打开它。我该怎么办？

I need to open a file in read/write mode, read its content and then clear all. So, I cannot open it in truncate mode. How can I do that?

推荐答案

讨厌让你失望，但是..

没有从打开的 std :: fstream 清除文件内容的标准方法，因此直接的方法是按实际的方式处理这两个操作。 two 操作。

Hate to disappoint you, but..

There's no standard way of clearing the contents of a file from an open std::fstream, the straight forward way is therefore to handle the two operations as what they really are.. two operations.

首先处理所有读取，然后处理写入（通过不同的 stream对象）。

First handle all the reading, and later the writing (through a different stream object).

首先以只读模式（ std :: ifstream ）打开文件并读取您感兴趣的数据，然后丢弃该文件句柄并再次打开文件。 。这次是在只写和截断模式（ std :: ofstream ）下进行的操作，以便清除文件内容。 / p>

In other words; first open the file in read-only mode (std::ifstream) and read the data you are interested in, then discard that file-handle and open the file again.. this time in write-only and truncation mode (std::ofstream), so that you will clear the contents of the file.

std::ifstream ifs ("some_file.txt");

... // read old data

ifs.close ();

std::ofstream ofs ("some_file.txt", std::ios::out | std::ios::trunc); // clear contents

... // write new data

ofs.close ();

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