test

Posted 2020-12-30 blog-yejy

C++代码

#include <iostream>
#include <functional>
#include <fstream>
#include <ostream>
#include <string>
#include <vector>
#include <algorithm>
#include <initializer_list>

int test()
{
    int a = 5;
    return a;
}

using namespace std;

void parserTest()
{
    string strLine;
}

void fun(char *)
{
    std::cout << "foo(char*) is called" << std::endl;
}

void fun(int)
{
    std::cout << "foo(int) is called" << std::endl;
}

constexpr int fibonacci ( const int n) 
{
    return n == 1 || n == 2 ? 1 : fibonacci (n -1) + fibonacci (n -2);
}

class initializer_list_Test
{
public:
    initializer_list_Test(std::initializer_list<int> list)
    {
        for(std::initializer_list<int>::iterator itr = list.begin(); itr != list.end(); itr++)
        {
            m_vecTest.push_back(*itr);
        }
    }   

    std::vector<int> m_vecTest;
};

template<typename T, typename U>
auto add(T a, U b) -> decltype(a + b)
{
    return a + b;
}

int main()
{
    // std::function
    std::function<int(void)> function_Test;

    function_Test = nullptr;

    try
    {
        function_Test();
    }
    catch(std::bad_function_call e)
    {
        std::cout << e.what() << std::endl; 
    }

    function_Test = test;

    std::cout << function_Test()<< std::endl;

    // lamda
    /** [ captures ] <tparams>(optional)(c++20) ( params ) specifiers exception attr -> 
      *               ret requires(optional)(c++20) { body }    (1) 
      * [ captures ] ( params ) -> ret { body } (2) 
      * [ captures ] ( params ) { body }    (3) 
      * [ captures ] { body }   (4) 
    */
    int test_param1 = 56;

    auto f = [](int test_param1){return test_param1;};

    auto test_param2 = [=](int i = 6)mutable noexcept(true)-> int{ i += 12; test_param1 += 1; return test_param1 + i;}; 

    bool bTest = true;
    
    int a = static_cast<int>(bTest);

    std::cout <<  test_param2() << "  " << a << std::endl;


    // nullptr
    if(std::is_same<decltype(NULL), decltype(0)>::value)
        std::cout << "null == 0" << std::endl;
    if(std::is_same<decltype(NULL), decltype((void*)0)>::value)
        std::cout << "null == (void *)0" << std::endl;
    if(std::is_same<decltype(NULL), decltype(nullptr)>::value)
        std::cout << "null == nullptr" << std::endl;

    fun(0);
    fun(nullptr);
    //fun(NULL);

    // constexpr
    int arr_i[fibonacci(6) + 1] = {0};

    std::cout << arr_i[5] << std::endl;

    //if declare param C++ 17
    // std::vector<int> vecTest = {1,2,3,4};

    // if(std::vector<int>::iterator itr = std::find(vecTest.begin(),vecTest.end(),3); itr != vecTest.end())
    // {
    //  *itr = 10;
    // }

    // initializer_list   可以作为类construct的形参类型，也可以作为普通函数的形参类型
    initializer_list_Test initializer_Test{0,1,2,3,4,5};

    for(auto itr = initializer_Test.m_vecTest.begin(); 
        itr != initializer_Test.m_vecTest.end(); ++ itr)
    {
        std::cout << *itr << std::endl;
    }

    auto arr = new auto(10);

    //类型推导  auto decltype 
    std::cout <<add<int, double>(5,3.0)<< std::endl;
    auto q = add<int, double>(50, 3.12);
    if(std::is_same<decltype(q), double>::value)
    {
        std::cout << "decltype(q) == double" << std::endl;
    }
 
    return 0;
}