stl vector 函数_vector :: at（）函数以及C ++ STL中的示例

stl vector 函数

C ++ vector :: at()函数 (C++ vector::at() function)

vector::at() is a library function of "vector" header, it is used to access an element from specified position, it accepts a position/index and returns the reference to the element at specified position/index.

vector :: at()是“ vector”头文件的库函数，用于从指定位置访问元素，它接受位置/索引并返回对指定位置/索引处的元素的引用。

Note: To use vector, include <vector> header.

注意：要使用向量，请包含<vector>标头。

Syntax of vector::at() function

vector :: at()函数的语法

    vector::at(size_type n);

Parameter(s): void – It is a position of an element to be accessed.

参数： void –这是要访问的元素的位置。

Return value: reference – It returns a reference to the element at position n.

返回值： reference –返回对位置n处元素的引用。

Example:

例：

    Input:
vector<int> vector1{ 1, 2, 3, 4, 5 };
Function call:
cout << vector1.at(0) << endl;
cout << vector1.at(1) << endl;
Output:
1
2

C ++程序演示vector :: at()函数的示例 (C++ program to demonstrate example of vector::at() function)

//C++ STL program to demonstrate example of
//vector::at() function
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> v1{ 10, 20, 30, 40, 50 };
//accessing elements
cout << "first element : " << v1.at(0) << endl;
cout << "second element: " << v1.at(1) << endl;
cout << "last element  : " << v1.at(v1.size() - 1) << endl;
//accessing all elemenets
cout << "all elements of vector v1..." << endl;
for (int i = 0; i < v1.size(); i++)
cout << "element at index " << i << " : " << v1.at(i) << endl;
return 0;
}

Output

输出量

first element : 10
second element: 20
last element  : 50
all elements of vector v1...
element at index 0 : 10
element at index 1 : 20
element at index 2 : 30
element at index 3 : 40
element at index 4 : 50

Reference: C++ vector::at()

参考： C ++ vector :: at()