x.others

cpp11 一些新的std标准库函数，新的特性。还有一些个人感觉不咋用的，未记录。

std::move & std::forward

详见移动语义

std::thread

详见上面

std::to_string

能将数字转换为字符串

std::to_string(1.2); // == "1.2"
std::to_string(123); // == "123"

smart pointer 智能指针

std::unique_ptr

std::share_ptr

std::weak_ptr

std::make_share

详见上面

std::tuple

std::tuple，元组定义了一个有固定数目元素的容器,其中的每个元素类型都可以不相同

通过make_tuple()创建元组，通过get<>()来访问元组的元素，如下：

auto t1 = std::make_tuple(10, "Test", 3.14);

std::cout << "The value of t1 is "

    << "(" << std::get<0>(t1) << ", " << std::get<1>(t1)

    << ", " << std::get<2>(t1) << ")\n";
int n = 1;

auto t2 = std::make_tuple(std::ref(n), n);//ref表示引用

n = 7;

std::cout << "The value of t2 is "

          << "(" << std::get<0>(t2) << ", " << std::get<1>(t2) << ")\n";

输出

The value of t1 is (10, Test, 3.14)
The value of t2 is (7, 1)

std::tie

和tuple配合使用，tuple可以理解为打包，tie可以理解为解包

// With tuples...
std::string playerName;
std::tie(std::ignore, playerName, std::ignore) = std::make_tuple(91, "John Tavares", "NYI");

// With pairs...
std::string yes, no;
std::tie(yes, no) = std::make_pair("yes", "no");

std::ref

std::ref 用于取某个变量的引用，这个引入是为了解决一些传参问题

std::bind 和多线程的 std::thread 是必须显式通过 std::ref 来绑定引用进行传参，否则，形参的引用声明是无效的。

如下例子：

#include<functional>
#include<iostream>

#include<thread>
#include<string>

void threadFunc(std::string &str, int a)
{
    str = "change by threadFunc";
    a = 13;
}

void f(int& n1, int& n2, const int& n3)
{
    std::cout << "In function: " << n1 << ' ' << n2 << ' ' << n3 << '\n';
    ++n1; // increments the copy of n1 stored in the function object
    ++n2; // increments the main()'s n2
    // ++n3; // compile error
}

int main()
{
    int n1 = 1, n2 = 2, n3 = 3;
    std::function<void()> bound_f = std::bind(f, n1, std::ref(n2), std::cref(n3));
    n1 = 10;
    n2 = 11;
    n3 = 12;
    std::cout << "Before function: " << n1 << ' ' << n2 << ' ' << n3 << '\n';
    bound_f();
    std::cout << "After function: " << n1 << ' ' << n2 << ' ' << n3 << '\n';
    
    std::string str("main");
    int a = 9;
    std::thread th(threadFunc, std::ref(str), a);

    th.join();

    std::cout<<"str = " << str << std::endl;
    std::cout<<"a = " << a << std::endl;
    
    return 0
}

结果输出：

Before function: 10 11 12
In function: 1 11 12
After function: 10 12 12

str = change by threadFunc
a = 9

std::begin/end

template <typename T>
int CountTwos(const T& container) {
  return std::count_if(std::begin(container), std::end(container), [](int item) {
    return item == 2;
  });
}

std::vector<int> vec = {2, 2, 43, 435, 4543, 534};
int arr[8] = {2, 43, 45, 435, 32, 32, 32, 32};
auto a = CountTwos(vec); // 2
auto b = CountTwos(arr);  // 1