STL vector中的shrink_to_fit方法(32)

原文地址:http://www.cplusplus.com/reference/vector/vector/shrink_to_fit/ public member function <vector>

std::vector::shrink_to_fit

void shrink_to_fit();      

Shrink to fit Requests the container to reduce its capacity to fit its size.

请求容器降低其容量和size匹配。

The request is non-binding, and the container implementation is free to optimize otherwise and leave the vector with a capacity greater than its size.

该请求不具有约束力，容器可以自由地去执行其他的优化方案（capacity可以大于size）。//我查了一下网上说是该方法由编译器决定是否真正释放多余的内存，该方法值是提出请求，是否要实现由编译器说了算。

例子:

// vector::shrink_to_fit
#include <iostream>
#include <vector>
using namespace std;
int main ()
{
  std::vector<int> myvector (100);
  std::cout << "1. capacity of myvector: " << myvector.capacity() << '\n';	
  cout<<"size="<<myvector.size()<<endl;

  myvector.resize(10);
  std::cout << "2. capacity of myvector: " << myvector.capacity() << '\n';
     cout<<"size="<<myvector.size()<<endl;
  myvector.shrink_to_fit();
  std::cout << "3. capacity of myvector: " << myvector.capacity() << '\n';
	  cout<<"size="<<myvector.size()<<endl;
  return 0;
}
           

结果截图:

This may cause a reallocation, but has no effect on the vector size and cannot alter its elements.

这可能导致重分配，但不会影响其size以及不能改变其元素。

Parameters

none

Return value

none

Example

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

// vector::shrink_to_fit #include <iostream> #include <vector> int main () { std::vector<int> myvector (100); std::cout << "1. capacity of myvector: " << myvector.capacity() << '\n'; myvector.resize(10); std::cout << "2. capacity of myvector: " << myvector.capacity() << '\n'; myvector.shrink_to_fit(); std::cout << "3. capacity of myvector: " << myvector.capacity() << '\n'; return 0; }

Edit & Run

Possible output:

1. capacity of myvector: 100 2. capacity of myvector: 100 3. capacity of myvector: 10

Complexity

At most, linear in container size.

与容器大小线性相关。

Iterator validity

If a reallocation happens, all iterators, pointers and references related to the container are invalidated.

如果发生重分配，所有的迭代器，指针以及引用都将失效。

Otherwise, no changes.

否则，不会改变其有效性。

Data races

The container is modified.

容器将被修改。

If a reallocation happens, all contained elements are modified.

如果发生重分配，所有容器内元素都将被修改。

Otherwise, no contained elements are accessed.

否则，元素不会被访问。

Exception safety

If the type of the elements is either copyable or no-throw moveable, there are no changes in the container in case of exception (strong guarantee).

如果元素的复制构造以及移动构造不会抛出异常，那么容器抛出异常的规则不变。

Otherwise, if an exception is thrown, the container is left with a valid state (basic guarantee).

否则，如果容器抛出异常，容器依旧承诺保持在有效状态。

//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。

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2014-8-19

于GDUT