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c++特性

admin 11月 14, 2020 0

Lambda expressions



auto g = [](int x){return x * x;};
std::cout << g(3); // 9

作为predict

1 2	std::vector<int> s = {1, 2, 3, 5}; std::cout << std::all_of(s.begin(), s.end(), [](int x) { return x > 0;}) << "n"; // 1

range-based for loop

// for( range_declaration: range_expression) loop statement

std::vector<int> s = {1, 2, 3, 4};
for(auto& i : s){
    std::cout << i << std::endl;
}

functor

A functor (or function object) is a C++ class that acts like a function. Functors are called using the same old function call syntax. To create a functor, we create a object that overloads the operator().

// C++ program to demonstrate working of 
// functors. 

using namespace std; 
  
// A Functor 
class  
{ 
private: 
    int num; 
public: 
    increment(int n) : num(n) {  } 
  
    // This operator overloading enables calling 
    // operator function () on objects of increment 
    int operator () (int arr_num) const { 
        return num + arr_num; 
    } 
}; 

int main() 
{ 
    int arr[] = {1, 2, 3, 4, 5}; 
    int n = sizeof(arr)/sizeof(arr[0]); 
    int to_add = 5; 
  
    transform(arr, arr+n, arr, increment(to_add)); 
  
    for (int i=0; i<n; i++) 
        cout << arr[i] << " "; 
}

unique_ptr

每一个unique_ptr与一个raw_ptr绑定,当unique_ptr out of scope, 会释放raw_ptr分配的内存

特点

无法copy或者assign，只能在unique_ptr之间用std::move进行移动

#include <iostream>
#include <memory>

struct Task
{
    int mId;
    Task(int id ) :mId(id)
    {
        std::cout<<"Task::Constructor"<<std::endl;
    }
    ~Task()
    {
        std::cout<<"Task::Destructor"<<std::endl;
    }
};

int main()
{
    // Create a unique_ptr object through raw pointer
    std::unique_ptr<Task> taskPtr(new Task(23));
    // auto taskPtr = new Task(23); //leak
    //Access the element through unique_ptr
    int id = taskPtr->mId;

    std::cout<<id<<std::endl;


    return 0;
}

shared_ptr/weak_ptr