array详解

        array是C++11中新提出来的容器类型，与内置数组相比，array是一种更容易使用，更加安全的数组类型，可以用来替代内置数组。作为数组的升级版，继承了数组最基本的特性，也融入了很多容器操作。array和数组一样，是一种固定大小的容器类型，在定义的时候就要声明大小和类型。

1、Iterators

示例

void IteratorsTest()
{
    std::array<int,5> myarray = { 2, 16, 77, 34, 50 };

    std::cout << "myarray contains:";
    for ( auto it = myarray.begin(); it != myarray.end(); ++it )
        std::cout << ' ' << *it;
    std::cout << '\n';

    std::cout << "myarray const contains:";
    for ( auto it = myarray.cbegin(); it != myarray.cend(); ++it )
        std::cout << ' ' << *it;   // cannot modify *it
    std::cout << '\n';

    std::cout << "myarray resever contains:";
    for ( auto rit=myarray.rbegin() ; rit < myarray.rend(); ++rit )
        std::cout << ' ' << *rit;
    std::cout << '\n';

    std::cout << "myarray resever const backwards:";
    for ( auto rit=myarray.crbegin() ; rit < myarray.crend(); ++rit )
        std::cout << ' ' << *rit;   // cannot modify *rit
    std::cout << '\n';
}

运行结果：

myarray contains: 2 16 77 34 50
myarray const contains: 2 16 77 34 50
myarray resever contains: 50 34 77 16 2
myarray resever const backwards: 50 34 77 16 2

2、Capacity

size(): 返回元素个数

max_size(): 返回vector最大能放元素个数

empty():容器是否为空

示例

void CapacityTest()
{
    std::array<int,5> myints;
    std::cout << "size of myints: " << myints.size() << std::endl;
    std::cout << "sizeof(myints): " << sizeof(myints) << std::endl;
    std::cout << "max_size of myints: " << myints.max_size() << '\n';

    std::array<int,0> first;
    std::array<int,5> second;
    std::cout << "first " << (first.empty() ? "is empty" : "is not empty") << '\n';
    std::cout << "second " << (second.empty() ? "is empty" : "is not empty") << '\n';
}

运行结果

size of myints: 5
sizeof(myints): 20
max_size of myints: 5
first is empty
second is not empty

3、Element access

operator[]: 同数组方式取值

at():返回第n个元素的引用

front():返回第一个元素的引用

back():返回最后一个元素的引用

data():返回第一个元素的指针

示例：

void ElementAccess()
{
    std::array<int,10> myarray;
    for (int i=0; i<10; i++) 
        myarray[i]=i;
    std::cout << "myarray contains:";
    for (int i=0; i<10; i++)
        std::cout << ' ' << myarray.at(i);
    std::cout << '\n';
    std::cout << "front is: " << myarray.front() << std::endl;   
    std::cout << "back is: " << myarray.back() << std::endl;   

    const char* cstr = "Test string";
    std::array<char,12> charray;
    std::memcpy (charray.data(),cstr,12);
    std::cout << charray.data() << '\n';  
}

运行结果：

myarray contains: 0 1 2 3 4 5 6 7 8 9
front is: 0
back is: 9
Test string

4、Modifiers

fill():设置所有元素的值

swap():交换容器内容

示例：

void ModifiersTest()
{
    std::array<int,6> myarray;
    myarray.fill(5);
    std::cout << "myarray contains:";
    for ( int& x : myarray) 
    { std::cout << ' ' << x; }
    std::cout << '\n';

    std::array<int,5> first = {10, 20, 30, 40, 50};
    std::array<int,5> second = {11, 22, 33, 44, 55};
    first.swap (second);
    std::cout << "first:";
    for (int& x : first) std::cout << ' ' << x;
    std::cout << '\n';
    std::cout << "second:";
    for (int& x : second) std::cout << ' ' << x;
    std::cout << '\n';
}

运行结果：

myarray contains: 5 5 5 5 5 5
first: 11 22 33 44 55
second: 10 20 30 40 50