std::deque::at

      reference at (size_type n);
const_reference at (size_type n) const;

Returns a reference to the element at position n in the deque container object.

返回在特定位置元素的引用。

The function automatically checks whether n is within the bounds of valid elements in the container, throwing an out_of_range exception
if it is not (i.e., if n is greater or equal than its size). This is in contrast with member operator[],
that does not check against bounds.

该方法将自动检测n的合法性，如果n超出了范围，将抛出out_of_range异常。另一个相似的是operator[]方法，但是不会检测合法性。

例子：

#include <iostream>
#include <deque>
#include <vector>
using namespace std;
int main()
{
	deque<int> di{1,2,3,4,5};
	for(int i:di)
		cout<<i<<" ";
	cout<<endl;
	cout<<"di.at(0)="<<di.at(0)<<endl;
	cout<<"di.at(2)="<<di.at(2)<<endl;
	cout<<"di.at(3)="<<di.at(3)<<endl;
	cout<<"di.at(4)="<<di.at(4)<<endl;
	cout<<"di.at(5)="<<di.at(5)<<endl;
	cout<<"di.at(-1)="<<di.at(-1)<<endl;
	


}

Returns a reference to the element at position n in the deque container object.

返回deque容器特定位置的元素的引用。

The difference between this member function and member operator function operator[] is that deque::at signals
if the requested position is out of range by throwing an out_of_range exception.

和operator[]方法不同的是at在n不合法的时候会跑出out_of_range方法。

Parameters

n

Position of an element in the container.
If this is greater than the deque size, an exception of type out_of_range is
thrown.
Notice that the first element has a position of 0 (not 1).
Member type size_type is an unsigned integral type.

容器内元素的位置。

需要注意第一个元素的位置为0.

Return value

The element at the specified position in the container.

返回特定位置元素的引用。

If the deque object is const-qualified, the function returns a const_reference. Otherwise, it returns a reference.

Member types reference and const_reference are the reference types to the elements of the container (see deque member types).

Example

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// deque::at
#include <iostream>
#include <deque>

int main ()
{
  std::deque<unsigned> mydeque (10);   // 10 zero-initialized unsigneds

  // assign some values:
  for (unsigned i=0; i<mydeque.size(); i++)
    mydeque.at(i)=i;

  std::cout << "mydeque contains:";
  for (unsigned i=0; i<mydeque.size(); i++)
    std::cout << ' ' << mydeque.at(i);

  std::cout << '\n';

  return 0;
}

Output:

mydeque contains: 0 1 2 3 4 5 6 7 8 9

Complexity

Constant.

Iterator validity

No changes.

Data races

The container is accessed (neither the const nor the non-const versions modify the container).
Element n is potentially accessed or modified by the caller. Concurrently accessing or modifying other elements is safe.

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the container.

It throws out_of_range if n is out of bounds.

如果n不再范围内将抛出out_of_range异常。

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//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。

//今后的翻译将以简洁为主，翻译其主要意思，不再每句翻译。

转载请注明出处：http://blog.csdn.net/qq844352155
author:天下无双

Email:coderguang@gmail.com

2014-9-1

于GDUT

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