如何在C ++中以附加模式清除文件 [英] How to clear a file in append mode in C++

问题描述

我有一个文件，需要对其进行多次操作.有时我只想在文件末尾附加数据，有时我只想从文件中读取数据，有时我想擦除所有数据并从文件的开头写入.然后，我再次需要在文件末尾附加数据.

I've a file on which I require multiple operations. Sometimes I just want to append data at the end of the file, sometimes I just want to read from the file, and sometimes, I want to erase all the data and write form the beginning of the file. And then, I again need to append data at the end of file.

我正在使用以下代码:

ofstream writeToTempFile;
ifstream readFromTempFile;

writeToTempFile.open("tempFile.txt", ios::app | ios::out);
readFromTempFile.open("tempFile.txt", ios::in); 

// Reading and Appending data to the file
// Now it is time to erase all the previous data and start writing from the beginning


writeToTempFile.open("tempFile.txt", std::ofstream::trunc); // Here I'm removing the contents.

// Write some data to the file

writeToTempFile.open("tempFile.txt", std::ofstream::app); // Using this, I'm again having my file in append mode

但是我所做的无法正常工作.请给我建议一些C ++解决方案. (不在C中)

But what I've done doesn't work correctly. Please suggest me some solution in C++. ( Not in C)

推荐答案

代码存在的问题是:

在再次调用方法 open 之前，我没有关闭文件.

I wasn't closing the file before I called the method open again on it.

因此，在使用某些不同权限重新打开文件之前，请先close文件.

So, close the file before you re-open it with some different permissions.

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