STL vector总结(四) Element access(37)
如果容器的大小大于n,不会抛出异常。 否则,将导致未知的错误。 ——————————————————————————————————————————————————— public member function vector std:: vector::at reference at (size_type n);c
如果容器的大小大于n,不会抛出异常。
否则,将导致未知的错误。
———————————————————————————————————————————————————
public member function
std::vector::at
<span> reference at (size_type n); const_reference at (size_type n) const;</span>
返回一个指向位置n的元素的引用。
该方法将自动检测n是否是在一个有效的范围,如果不是则将抛出out_of_range异常。
另一个对照的方法是operator[],这个方法不会检测数据的有效性。
Parameters
- n
n是元素在vector中的位置。
如果n大于或者等于数组的size,那么将会抛出out_of_range异常。
注意,第一个元素的位置为0而不是1.
Return value
返回值为元素在容器内指定位置的值
当n不在范围内时抛出out_of_range异常。
__________________________________________________________________________________________________________________________________________
public member function
std::vector::front
<span> reference front(); const_reference front() const;</span>
访问第一个元素
返回第一个元素的引用。
和begin不一样,begin是返回一个迭代器,而front是返回一个直接引用。
对一个空的容器调用该方法将会导致不可预料的结果。
Parameters
noneReturn value
一个指向该vector容器中第一个元素的引用.
———————————————————————————————————————————————————
public member function
std::vector::back
<span> reference back(); const_reference back() const;</span>
返回最后一个元素的引用。
和end不一样的是,end是返回一个指向超尾元素的迭代器,而这个函数是直接返回一个引用。
对一个空的容器调用该方法会导致未知的行为。
Parameters
noneReturn value
返回值是一个指向vector中最后一个元素的引用。
—————————————————————————————————————————————————————————————————————————————
public member function
std::vector::data
<span> value_type* data() noexcept; const value_type* data() const noexcept;</span>
返回一个直接指向内存中存储vector元素位置的指针。
因为vector里面的元素都是顺序连续存放的,该指针可以通过偏移量来访问数组内的所有元素。
Parameters
noneReturn value
返回一个指针指向数组第一个元素所在的内存。
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//总结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。
author:天下无双
Email:coderguang@gmail.com
2014-8-27
于GDUT
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