什么是setw（）的处理？ [英] What's the deal with setw()?

问题描述

我最近被 ios_base :: width 和/或 setw 操纵器重置所有写入信息流的项目。

I recently was bitten by the fact that ios_base::width and/or the setw manipulator have to be reset with every item written to the stream.

也就是说，您必须这样做：

That is, you must do this:

while(whatever)
{
    mystream << std::setw(2) << myval;
}

而不是这样：

mystream.width(2);
while(whatever)
{
    mystream << myval;
}

好的。

但是有没有人知道为什么做这个设计决定呢？
有没有一些理由我缺少，或者这只是标准的一个黑暗的角落？

But does anyone know why this design decision was made? Is there some rationale that I'm missing, or is this just a dark corner of the standard?

其他流格式化修饰符SO问题）是粘性的，而 setw 不是。

Other stream formatting modifiers (as mentioned in the linked SO question) are 'sticky', while setw is not.

推荐答案

我看到的方式是：你可以总是做下面的事情，如果你想要统一应用。

The way i see it is : You can always do something like below if you want it to be applied uniformly.

int width =2;
while(whatever)
{
    mystream << std::setw(width) << myval;
}

但如果它是粘滞的，你提到：

but if it was sticky as you mention:

mystream.width(2);
while(whatever)
{
    mystream << myval;
}

如果我想要一个不同的宽度每行我必须保持设置宽度。

and if i wanted a different width every line I have to keep setting width.

因此，这两种方法几乎都是一样的，我会喜欢或不喜欢他们，取决于我现在在做什么。

So essentially both approaches are almost the same, and i would like or dislike them depending on what i am doing now.

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