这是什么“用于”做？它是如何工作的？ [英] What does this "for" do? How does it work?

问题描述

这是做什么的？它是如何工作的？



for（std :: vector< t>& column：mCells）{column.resize（mHeight）; }



我尝试了什么：



这是做什么的？它是如何工作的？



for（std :: vector< t>& column：mCells）{column.resize（mHeight）; }

What does this for do? How does it work?

for (std::vector<t>& column : mCells) { column.resize(mHeight); }

What I have tried:

What does this for do? How does it work?

for (std::vector<t>& column : mCells) { column.resize(mHeight); }

推荐答案

它适用于C ++中的每个循环，并迭代您（最有可能）网格中的列。它被称为基于范围的循环;因为你隐含了一个范围。



一旦获得专栏，它会将其调整到特定高度 - 同时注意参考符号。如果没有pass-by-reference，您的操作将对列没有影响。我创建的一个快速示例就是这里，

It is a for each loop in C++, and iterates over the columns that you have in your (most likely) grid. It is called a range-based loop; since you get a range implicitly in it.

And once it gets the column, it resizes it to a specific height—also notice the reference sign. Without the pass-by-reference your operation will have no effect on the columns. A quick example I created to demonstrate is here,

void processprint() {
    int array[] = { 1, 2, 3, 4 };
    
    // Increment the values, without modifying actual elements. 
    for (int item : array) {
        item += 2;
    }
    
    for (int item : array) {
        std::cout << item << std::endl;
    }
}

这将打印相同的数组，不会改变，但是如果你更改了这行，

This will print the same array, unaltered, however if you change the line,

void processprint() {
    int array[] = { 1, 2, 3, 4 };
    
    // Increment the values, change actual values.
    for (int& item : array) {
        item += 2;
    }
    
    for (int item : array) {
        std::cout << item << std::endl;
    }
}

现在将打印递增的值。在这里查看， C ++ Shell [ ^ ]



基于范围的循环（自C ++ 11开始） - cppreference.com [ ^ ]

This will now print incremented values. Check it out here, C++ Shell[^]

Range-based for loop (since C++11) - cppreference.com[^]

Quote：

它是如何工作的？

对你来说，它是神奇的工作！

你有没有计划问我们C ++的每一个不寻常的语法？

有人可以告诉我这是怎么回事声明有效吗？ [ ^ ]

为什么在方法声明结束时它们是= 0？ [ ^ ]

clone（）是什么意思？为什么他们是< gamepiece>？之后的方法和定义[ ^ ]

我遇到了麻烦：意思。 [ ^ ]

怎么会发生这种情况？ [ ^ ]

请告诉我这些例子中单个冒号的用途。 [ ^ ]

请告诉我这些单分号的用途是什么示例。 [ ^ ]

请帮助我理解&的使用在这个例子中。一直在搜索和搜索。 [ ^ ]



C ++提供了解释每种语法的文档。

您可以在互联网上找到教程。

For you, it work by magic !
Do you have plan to ask us every single unusual syntax of C++ ?
Can someone tell me how this if statement works?[^]
Why is their a "=0" at the end of the method declaration?[^]
What does clone() mean? And why is their a method and a definition after <gamepiece>?[^]
I am having trouble with : meaning.[^]
How is it that this can happen?[^]
Please tell me what the single colon is used for in these examples.[^]
Please tell me what the single semicolon is used for in these examples.[^]
Please help me understand the use of & in this example. Been searching and searching.[^]

C++ have documentation where every single syntax is explained.
Chances are that you can also find tutorials on internet.

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