STL vector中的clear方法（18）

原文地址:http://www.cplusplus.com/reference/vector/vector/clear/

public member function

<vector>

std::vector::clear

• C++98
• C++11

void clear() noexcept;

Clear content

Removes all elements from thevector(which are destroyed), leaving the container with asizeof0.

移除vector内所有元素（并销毁他们）,使容器大小为变为0（size而不是capacity）。

例子：

#include <iostream>
#include <vector>
using namespace std;
int main()
{
	vector<int> vi={10,20,30};
	cout<<"size="<<vi.size()<<endl;
	cout<<"capacity="<<vi.capacity()<<endl;
	vi.clear();
	cout<<"size="<<vi.size()<<endl;
	cout<<"capacity="<<vi.capacity()<<endl;
	cout<<"vi[1]="<<vi[1]<<endl;
	
}

运行结果:

发现数据还是没有被销毁阿。。。

A reallocation is not guaranteed to happen, and thevector capacityis not guaranteed to change due to calling this function. A typical alternative that forces a reallocation is to useswap:

vector<T>().swap(x); // clear x reallocating

不保证会发生重分配，也不保证该函数会改变capacity，另一个备选的发生重分配的是swap。

Parameters

none

Return value

none

Example

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

// clearing vectors #include <iostream> #include <vector> int main () { std::vector<int> myvector; myvector.push_back (100); myvector.push_back (200); myvector.push_back (300); std::cout << "myvector contains:"; for (unsigned i=0; i<myvector.size(); i++) std::cout << ' ' << myvector[i]; std::cout << '\n'; myvector.clear(); myvector.push_back (1101); myvector.push_back (2202); std::cout << "myvector contains:"; for (unsigned i=0; i<myvector.size(); i++) std::cout << ' ' << myvector[i]; std::cout << '\n'; return 0; }

Edit & Run

Output:

myvector contains: 100 200 300
myvector contains: 1101 2202

Complexity

Linear insize(destructions).
This may be optimized toconstant complexityfortrivially-destructible types(such as scalar or PODs), where elements need not be destroyed.

复杂度和其大小线性相关（析构）

最优复杂度可能是常量时间复杂度，因为可能其中的元素不需要析构。

Iterator validity

All iterators, pointers and references related to this container are invalidated.

所有的迭代器，指针以及引用都将失效。

#include <iostream>
#include <vector>
using namespace std;
int main()
{
	vector<int> vi={10,20,30};
	cout<<"size="<<vi.size()<<endl;
	cout<<"capacity="<<vi.capacity()<<endl;
	int &ri=vi[0];
	auto it=vi.begin();
	vi.clear();
	cout<<"size="<<vi.size()<<endl;
	cout<<"capacity="<<vi.capacity()<<endl;
	cout<<"vi[1]="<<vi[1]<<endl;
	cout<<"ri="<<ri<<endl;
	cout<<"vi.begin()="<<*it<<endl;
	
}

坑我的吧，怎么都没有失效？？

Data races

The container is modified.
All contained elements are modified.

容器将被访问。

所有容器元素都将被修改。

Exception safety

No-throw guarantee:this member function never throws exceptions.

该成员方法不会抛出异常。

//翻译的不好的地方请多多指导，可以在下面留言或者点击左上方邮件地址给我发邮件，指出我的错误以及不足，以便我修改，更好的分享给大家，谢谢。

转载请注明出处：http://blog.csdn.net/qq844352155

2014-8-15

于GDUT