C++ 向量::清除 [英] C++ vector::clear

问题描述

vector <weight> decoy;

void clear_decoy() {  

    decoy.clear();   

    vector<weight> (decoy).swap(decoy);  
}

在上面的方法clear_decoy()中，vector (decoy).swap(decoy); 是什么意思?

In the above method clear_decoy(), what does vector<weight> (decoy).swap(decoy); mean please?

该方法是否清除decoy?谢谢！

Does the method clear decoy or not? Thanks!

推荐答案

它创建一个新的 Weight 对象向量(将为空)并与 decoy 交换.

It creates a new vector of Weight objects (which will be empty) and swaps it with decoy.

这样做的原因是默认情况下，std::vector 通常实际上并没有减少向量使用的存储空间，它只是破坏了包含在其中的所有对象.这样，向量就有空间存储更多的对象，而无需在未来重新分配.

The reason for this is that by default, std::vector<t>::clear often doesn't actually reduce the storage used by a vector, it merely destroys all the objects contained there. This way, the vector has room to store more objects without reallocation in the future.

但是，有时您想修剪向量中的容量.与新创建的向量(它一直存在到它的行尾，因此在那里被销毁)交换会释放向量分配的所有内存.

Sometimes, however, you want to trim the capacity in the vector. Swapping with a newly created vector (which lives until the end of it's line, and is therefore destroyed there) frees all the memory allocated by the vector.

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