C ++：ios :: app在fstream中不需要ios :: out [英] C++: ios::app doesnt need ios::out in fstream

问题描述

我在另一天用文件流对象中的标志进行测试

我这样做了。

  fstream binf（h.txt，ios :: app）; 
 binf<< 嘿; 
  

使用fstream，因为我没有使用 ios :: out

我注意到输出操作使用 ios :: app code>只有，但如果我使用任何其他标志不 ios :: out 它不工作

任何人告诉我为什么我只能使用 ios :: app 而不输出 ios :: out

解决方案

使用 app code>。

标准规定 app 和 out | app 具有相同的结果，相当于在模式a中的C fopen。

i was testing with flags in file stream objects the other day

And i did this.

fstream binf("h.txt", ios::app);
binf << "hey";

With fstream since i didnt use ios::out, the output operation shouldnt have worked , but it does work

I noticed that the the output operation works with ios::app only but if i use any other flag without ios::out it doesnt work

Can anyone tell me why I was able to output to the file while using only ios::app without ios::out

解决方案

Using app implies out.

The standard specifies that app and out|app have the same result, equivalent to C fopen in mode "a".

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