C++11/14/17 新特性总结

initializer_list

 std::vector<int> vctInts({92, 12, 39, 46, 92, 84, -1, 0, -234});

auto

 std::vector<int> vctInts({92, 12, 39, 46, 92, 84, -1, 0, -234});for (const auto& item : vctInts){std::cout << item << std::endl;}

decltype

用于模板函数的参数返回类型声明

template <typename T, typename U>
auto MyFunc(T t, U u) -> decltype(t + u)
{return t + u;
}

用于对lambda函数类型自动推导

 auto func = [](int a, double b, const std::string& strTmp)->std::string {boost::format fmt("%1%  %2%  %3%");fmt % a% b% strTmp;return fmt.str();};/*auto func2 = [](int a, double b, const std::string& strTmp)->std::string {char buf[1024] = { 0 };memset(buf, 0, sizeof(buf));sprintf_s(buf, "%d %.8f %s", a, b, strTmp.c_str());return std::string(buf);};*/std::map<int, decltype(func)> fucMap;fucMap.insert( std::make_pair(0,   func) );//fucMap.insert( std::make_pair(1, );auto it = fucMap.find(0);BOOST_CHECK_EQUAL( fucMap.end()== it, false);std::cout << it->second(10, 1.23, std::string("hello")) << std::endl;

override 和 final

override 用于来声明重写父类虚函数
final 用来修饰一个类是,表明一个类禁止被继承; 用来修饰虚函数时, 表明虚函数不能被重写

函数返回类型后置 (用于模板函数)
模板别名: using


typedef std::vector<std::map<std::string, std::string>>::iterator  itMaps;
using itMaps = std::vector<std::map<std::string, std::string>>::iterator  ;

using可以用于模板的别名定义, typedef 则不可以

template<typename T>
using it12Items = std::array<T, 12>;

nullptr
用来取代 NULL


0 == nullptr;  //true
NULL == nullptr;  //true

智能指针

shared_ptr
unique_ptr
weak_ptr

异常规范


foo()noexcept
foo()noexcept(false)
foo()noexcept(true)

explicit

C++11之前仅限制单个参数的构造函数做隐式转换
C+++11开始不限于单个参数的构造函数

可变参数模板
一般用递归的方式逐步减少参数的个数 , 递归终止于0个参数


//递归结束
void XPrint()
{
}template< typename T, typename ...Types>
void XPrint(const T& first,  const Types&... otherArgs)
{PlainPrint(first);XPrint( otherArgs... );
}BOOST_AUTO_TEST_CASE(test_variadic_templates)
{std::cout << "hello  ............" << std::endl;XPrint(2, 5.231, std::string("hello"), "niuniu", std::complex(5, 1));}

右值引用和移动语义

注意自己实现移动拷贝(move ctor)的时候(有指针), 收尾时需要将被move的对象的指针设置为NULL


std::vector<std::string> vctInts;
vctInts.push_back(std::move( std::string("hello") ));

原生字符串支持

//std::string  strFilePath1 = "C:\\Program Files (x86)\\Tencent\\QQ\\gf-config.xml"; //ok//std::string  strFilePath1 = R"(D:\gradle-6.0-bin.zip)"; //okstd::string  strFilePath1 = R"(C:\Program Files (x86)\Tencent\QQ\gf-config.xml)"; //okstd::filesystem::path p1( strFilePath1 ); //filesystem是 C++17标准
if (filesystem::exists(p1)){std::cout << "exists" << std::endl;
}else{std::cout << "not exists" << std::endl;
}std::ifstream infstream( strFilePath1, ios::in | ios::binary);
if(infstream.is_open())
{char buf[1024] { 0 };memset(buf, 0, sizeof(buf));while (!infstream.eof()){infstream.getline(buf, 1024);std::cout << buf << std::endl;}infstream.close();
}
else
{std::cout << "open file failed." << std::endl;
}

filesystem 文件系统
chrono 时间
regex 正则表达式

以下内容, 移至 C++11并发编程中做介绍

atomic 原子操作

https://en.cppreference.com/w/cpp/atomic

关于std::memory_order: https://www.cnblogs.com/lizhanzhe/p/10893016.html
std::thread
std::mutex
std::future
std::atomic
std::async

/**
*Date: 2019/11/30 13:24
*Author:yqq
*Descriptions:C++11  C++14  C++17 的一些新的特性*/
#ifdef _WIN32
#define _CRT_SECURE_NO_WARNINGS
#endif
#include <cstdio>
#include <iostream>
#include <vector>
#include <array>
#include <complex>#define  BOOST_TEST_MAIN
#include "boost/algorithm/string.hpp"
#include "boost/format.hpp"
#include "boost/test/included/unit_test.hpp"using namespace std;BOOST_AUTO_TEST_SUITE(test_cpp11)BOOST_AUTO_TEST_CASE(test_char16_t)
{const char16_t* ch16Chinese = u"中文のああㅝㅒㅖㄸЩПЁξζ∰㏒";const char32_t* ch32Chinese = U"中文のああㅝㅒㅖㄸЩПЁξζ∰㏒";const wchar_t* wchChinese = L"中文のああㅝㅒㅖㄸЩПЁξζ∰㏒";std::wcout << ch16Chinese << std::endl;std::wcout << ch32Chinese << std::endl;std::cout << "--------" << std::endl;std::wcout << wchChinese << std::endl;wprintf(wchChinese);std::cout << "hello" << std::endl;
}BOOST_AUTO_TEST_CASE(test_uniforminitialize)
{int d{ 10 };char ch {90};std::vector<int> a1{ 100, 99, 123 };std::cout << "size : " << a1.size() << std::endl;for (auto item : a1) {std::cout << item << std::endl;}}struct CTemp
{//CTemp(std::initializer_list<int> &initList) //errorCTemp(std::initializer_list<int> initList) //ok{for (auto item : initList){m_vctNumbers.push_back(item);}/*m_vctNumbers(initList);*/ //error}~CTemp() {}void Show(){for (auto item : m_vctNumbers){std::cout << item << std::endl;}}//void Set(std::initializer_list<int>& ilstArgs) //不支持引用方式//void Set(std::initializer_list<int> *ilstArgs) //不支持指针void Set(std::initializer_list<int> ilstArgs){m_vctNumbers.clear();//for (auto item : *ilstArgs)for (auto item : ilstArgs){m_vctNumbers.push_back(item);}}std::vector<int> m_vctNumbers;
};BOOST_AUTO_TEST_CASE(test_initialize_list)
{//该语法只能用于构造函数, 但是initializer_list可以当做模板来用CTemp  tmp{ 3, 9, 2, 88, 12, 93 }; tmp.Show();tmp.Set({1, 3, 9, -134});tmp.Show();
}template <typename T>
void MyTest(T a, T b)
{typedef std::array<T, 10> arr10;using arr11 = std::array<T, 11>;arr10 arrTst;arrTst[0] = a;arrTst[9] = b;std::cout << arrTst[9] << std::endl;arr11 arr11Tst;arr11Tst[0] = a;arr11Tst[10] = b;std::cout << arr11Tst[10] << std::endl;}template < typename T >
using arr20 = std::array<T, 20>;
//typedef arr20 = std::array<T, 20>; //错误, typedef不支持BOOST_AUTO_TEST_CASE(test_using)
{//使用 typedef 取别名typedef std::vector<int>::iterator   vctit;using vctit2 = std::vector<int>::iterator ;std::vector<int> vctTst{1, 39, 99};vctit itBegin = vctTst.begin();vctit2 itBegin2 = vctTst.begin();std::cout << (itBegin == itBegin2) << std::endl;std::cout << *itBegin << std::endl;MyTest<int>( 7, 9);arr20<double> arr20Test{ 0.99923, 1.342, 9 };for (auto item : arr20Test){std::cout << item << std::endl;}
}
template <typename T, typename U>
auto MyFunc(T t, U u) -> decltype(t + u)
{return t + u;
}struct CPear
{CPear(std::string strName) : m_strName(strName){}std::string m_strName;
};struct CPearApple
{CPearApple(std::string strName) :m_strName(strName){}std::string m_strName;
};struct CApple
{CApple(std::string strName) : m_strName(strName){}CPearApple operator+ (const CPear& pear){return CPearApple(pear.m_strName + m_strName);}std::string m_strName;
};BOOST_AUTO_TEST_CASE(test_functionreturntype)
{std::complex a(1, -2);std::complex  b(2, -3);auto c  =  MyFunc( a , b );std::cout << c << std::endl;CPear pear("pear");CApple apple("apple");auto pearApple = MyFunc(apple, pear);std::cout << pearApple.m_strName << std::endl;}
//BOOST_AUTO_TEST_CASE(test_testlabdafunctype)
{auto func = [](int a, double b, const std::string& strTmp)->std::string {boost::format fmt("%1%  %2%  %3%");fmt % a% b% strTmp;return fmt.str();};/*auto func2 = [](int a, double b, const std::string& strTmp)->std::string {char buf[1024] = { 0 };memset(buf, 0, sizeof(buf));sprintf_s(buf, "%d %.8f %s", a, b, strTmp.c_str());return std::string(buf);};*/std::map<int, decltype(func)> fucMap;fucMap.insert( std::make_pair(0,   func) );//fucMap.insert( std::make_pair(1, );auto it = fucMap.find(0);BOOST_CHECK_EQUAL( fucMap.end()== it, false);std::cout << it->second(10, 1.23, std::string("hello")) << std::endl;}class MyComplex
{public:MyComplex(int ir, int im = 0): _m_ir(ir), _m_im(im){_m_ino = 55 + ir;}//C++的数据限制是 "类" 级别的, 而不是对象级别, //所以同一类的  一个对象 再成员函数中可以修改 另一个对象的私钥或保护成员MyComplex & operator + (const MyComplex& cplx){_m_ir += cplx._m_ir;_m_im += cplx._m_im;std::cout << cplx._m_ino << std::endl;return *this;}protected:int _m_ir;int _m_im;private:int _m_ino;
};class MyComplexEx
{public:explicit MyComplexEx(int ir, int im = 0): _m_ir(ir), _m_im(im){_m_ino = 55 + ir;}//C++的数据限制是 "类" 级别的, 而不是对象级别, //所以同一类的  一个对象 再成员函数中可以修改 另一个对象的私钥或保护成员MyComplexEx& operator + (const MyComplexEx& cplx){_m_ir += cplx._m_ir;_m_im += cplx._m_im;std::cout << cplx._m_ino << std::endl;return *this;}protected:int _m_ir;int _m_im;private:int _m_ino;
};BOOST_AUTO_TEST_CASE(test_explicit)
{MyComplex  mcplx(5, -1);mcplx = mcplx + 5;   //这样是可以的, 编译做了隐式转换//_m_ir = 10//_m_imMyComplexEx  mcplxEx(5, -1);//mcplxEx = mcplxEx + 5;   //这样是不可以的, 显示地限制了隐式转换}BOOST_AUTO_TEST_SUITE_END()

可变参数模板

/**
*Date: 2019/12/21  14:27
*Author:yqq
*Descriptions:  C++11 可变参数模板
*/
#ifdef _WIN32
#define _CRT_SECURE_NO_WARNINGS
#endif
#include <cstdio>
#include <iostream>
#include <vector>
#include <array>
#include <complex>
#include <algorithm>
#include <ctime>#define  BOOST_TEST_MAIN
#include "boost/algorithm/string.hpp"
#include "boost/format.hpp"
#include "boost/test/included/unit_test.hpp"BOOST_AUTO_TEST_SUITE(test_cpp11)template<typename T>
void PlainPrint(const T& arg)
{std::cout << arg << std::endl;
}//函数模板不存在 "偏特化"
/*
template<>
void PlainPrint(const std::complex& cplx)
{std::cout << "复数: " << cplx << std::endl;
}
*///递归结束
void XPrint()
{}template< typename T, typename ...Types>
void XPrint(const T& first,  const Types&... otherArgs)
{PlainPrint(first);XPrint( otherArgs... );
}BOOST_AUTO_TEST_CASE(test_variadic_templates)
{std::cout << "hello  ............" << std::endl;XPrint(2, 5.231, std::string("hello"), "niuniu", std::complex(5, 1));}//实现编译时期的求最大值得函数
//#define  mymax( a, b )   ( a > b ? a : b )#ifdef max
#undef max
#endifint mymaximum(int n) //递归结束
{return n;
}template <typename ...Args>
int mymaximum(int nfirst, const Args&... arguments)
{return std::max(nfirst, mymaximum(arguments...));
}BOOST_AUTO_TEST_CASE(test_variadic_maximum)
{std::cout << "maximum is : " <<mymaximum(9, 1, -1, 22, -12, 10, 11, -9, 5, -23, 19, 21, 22)<< std::endl;//std::cout << mymax(9, 10) << std::endl;//std::cout <<  std::max( 9, 10 ) << std::endl;}BOOST_AUTO_TEST_CASE(test_move)
{std::vector <std::string>   vctStrs;const int iTestCount = 500;{#ifdef _WIN32DWORD   dwStart = ::GetTickCount();
#elseclock_t  clkStart = clock();
#endiffor (int i = 0; i < iTestCount; i++){//vctStrs.push_back( std::move( std::string("helllo")  )); //默认使用 push_back(T&&)std::string strTmp("hello");vctStrs.push_back(strTmp); //使用   push_back(T &)}#ifdef _WIN32DWORD   dwEnd = ::GetTickCount();std::cout << "duration: " << dwEnd - dwStart << std::endl;
#elseclock_t  clkEnd = clock();std::cout << "duration: " << clkEnd - clkStart << std::endl;
#endif}{#ifdef _WIN32DWORD   dwStart = ::GetTickCount();
#elseclock_t  clkStart = clock();
#endiffor (int i = 0; i < iTestCount; i++){//std::string strTmp("hello");vctStrs.push_back(std::move(std::string("hello"))); // 使用 push_back(T&& )}#ifdef _WIN32DWORD   dwEnd = ::GetTickCount();std::cout << "duration: " << dwEnd - dwStart << std::endl;
#elseclock_t  clkEnd = clock();std::cout << "duration: " << clkEnd - clkStart << std::endl;
#endif}}BOOST_AUTO_TEST_CASE(test_initializer_list)
{std::vector<int> vctInts({92, 12, 39, 46, 92, 84, -1, 0, -234});for (const auto& item : vctInts){std::cout << item << std::endl;}}BOOST_AUTO_TEST_SUITE_END()

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