c++11总结

客官°小女子只卖身不卖艺 2022-09-15 12:26 153阅读 0赞

**for**

**auto**

**decltype**

#include<iostream>
    #include<vector>
    #include<map>
    #include<unordered_map>
    #include<algorithm>
    
    using namespace std;
    
    /********
     * for( : )
     *
    *********/
    void Feach() {
            vector<int> v = {1, 2, 3};
            for(auto t : v) {
                    cout << t << endl;
            }
    
            for(auto& t : v) {
                    t += 1;
            }
    
            for(const auto& t : v) {
                    cout << t << endl;
            }
    }
    
    
    /********
     *for_each
     *lamda
     *auto
    *********/
    void Find() {
            unordered_multimap<char, int> m = {
                    {'a', 1},
                    {'a', 3},
                    {'b', 2},
            };
            auto v = m.equal_range('a');
    
    /*
            for_each(v.first, v.second, [](unordered_map<char, int>::value_type& x) { 
                            cout << x.second << endl;
                    });
    */
    
    
            for_each(v.first, v.second, [](decltype(m)::value_type& x) { 
                            cout << x.second << endl;
                    });
    
            for(auto it = v.first; it != v.second; ++it) {
                    cout << it->first << " " << it->second << endl;
            }
    }
    
    
    
    /********
     *decltype
     *
    *********/
    
    int F() {
            return 0;
    }
    void Fdecl() {
    
            int a = 0;
            decltype(a) b = 2;
    
            const int& a1 = a;
            decltype(a1) a2 = a;
            //a2 = 2; read-only
    
            decltype(2 * 5.0) c = 2.2; //double
    
            int* p = &a;
            decltype(p) p1 = p; //int*
    
            decltype(a + c) d = c;  //double
            decltype(a += c) e = a; //int&
            e = 1;
            cout << "a " << a << endl;
    
            decltype(F()) f = 0;
    }
    
    /********
     *auto
     *
    *********/
    void Fauto() {
            auto a = 2;
            auto b = new auto(2.2);
            cout << typeid(b).name() << endl;
            const auto* p = &a;
            auto p1 = p;
    
            auto& a1 = a;
            a1 = 3;
            const int& a2 = a;
            auto& a3 = a2;
            //a3 = 4; 保留const，编译报错：1
    
            const int c = 3;
            auto c1 = c;//去掉const
            c1 = 2;
    
    }
    
    int main() {
    
            int a = 0;
            int&& b = 0;
            cout << &b << endl;
            //int&& c = b;
    
            Fauto();
            //Feach();
            //Find();
            Fdecl();
            return 0;
    }

**模板： **

**decltype**

**using**

#include<iostream>
    #include<vector>
    #include<map>
    #include<unordered_map>
    #include<algorithm>
    
    class A {
    public:
            static int get() {
                    return 0;
            }
    };
    
    class B {
    public:
            static int* get() {
                    return new int(3);
            }
    };
    
    /********
     *auto推导
     *原始方法
    *********/
    template <class T>
    void F() {
            auto v = T::get();
    }
    
    template <class T, class U>
    void F1() {
            T v = U::get();
    }
    
    
    /********
     *返回类型推导
     *
    *********/
    template <class R, class X, class Y>
    R F2(X a, Y b) {
            return a + b;
    }
    
    template <class X, class Y> //推导返回类型
    decltype((*(X*)0) + Y()) F3(X a, Y b) {
            return a + b;
    }
    
    template <class X, class Y> //返回类型后置
    auto F4(X a, Y b) -> decltype(a+b) {
            return a + b;
    }
    
    int main() {
            F<A>();
            F<B>();
    
            F1<int,A>();
            F1<int*,B>();
    
            int a = 1;
            float b = 1.2;
            std::cout << F2<int>(a, b) << std::endl;
            std::cout << F2<decltype(a+b)>(a, b) << std::endl;//我们不需要知道返回类型
            std::cout << F3(a, b) << std::endl;
            std::cout << F4(a, b) << std::endl;
    
            return 0;
    }

#include<iostream>
    #include<vector>
    #include<map>
    #include<unordered_map>
    #include<algorithm>
    using namespace std;
    
    
    /********
     *decltype处理模板特化
     *
    *********/
    template <class T>
    class A {
            typename T::iterator it_;
    public:
            void F(T& it) {
                    it_ = it.begin();
            }
    };
    
    
    //模板特化
    template <class T>
    class A<const T> {
            typename T::const_iterator it_;
    public:
    
            void F(const T& it) {
                    it_ = it.begin();
            }
    };
    
    
    //更简洁的方法
    template <class T>
    class B {
            decltype(T().begin()) it_;
    public:
            void F(T& it) {
                    it_ = it.begin();
            }
    
    };
    
    void Fiterator() {
            typedef vector<int> V_CT;
    
            const V_CT v;
            //const V_CT::iterator it = v.begin(); error
    
            //A<const V_CT> a;
            A<decltype(v)> a;
            a.F(v);
    
    
            V_CT v1;
            A<V_CT> b;
            b.F(v1);
    
            const V_CT v2;
            A<decltype(v)> c;
            c.F(v2);
    
    
    }
    
    /********
     * using
     *
    *********/
    template<class T>
    struct C {
            typedef map<int, T> M_TYPE;
    
    };
    
    
    //重定义模板
    template<class T>
    using M_TYPE1 = map<int, T>;
    
    
    void FMap() {
            C<string>::M_TYPE s;
            M_TYPE1<string> s1;
    }
    
    void test(int v) {
            cout << v << endl;
    }
    
    int test1(int v) {
            cout << v << endl;
    }
    
    template<class T>
    struct FD {
            typedef void(*FUN_TYPE)(T);
    };
    
    template<class T>
    using FUN_TYPE1 = void(*)(T);
    
    
    void Fpointer() {
            FD<int>::FUN_TYPE f1 = test;
            (*f1)(2);
    
            //FUN_TYPE1<int> f2 = test1; error
            FUN_TYPE1<int> f2 = test; 
            f2(2.2);
    }
    
    template <class R = int, class T>
    R F(T v) {
            return v;
    }
    
    int main() {
            Fiterator();
            FMap();
            cout << F(2.2) << endl;//从右向左填充模板参数
            return 0;
    }

**function**

**bind**

**smart ptr**

#include<iostream>
    #include<vector>
    #include<map>
    #include<unordered_map>
    #include<algorithm>
    #include<memory>
    using namespace std;
    
    
    /********
     *smart prt
     *
    *********/
    class A {
    public:
            static void* Create() {
                    return (void*) new int(3);
            }
    
            static void Destroy(void* p) {
                    if (p != NULL) {
                            cout << "Destroy" << endl;
                            delete (int*)p;
                    }
            }
    };
    
    void Fptr() {
            shared_ptr<int> p(new int(1));
            shared_ptr<int> p1 = p;
            cout << p.use_count() << endl;
            p1.reset();
            cout << p.use_count() << endl;//weak count
    
            shared_ptr<int> p2;
            p2.reset(new int(1));
            if (p2) {
                    int* sp = p2.get();
                    cout << "not null " << *sp << endl;
            }
    
            shared_ptr<int> p3 = make_shared<int>(2);
    
            unique_ptr<int> u(new int(1));
            //unique_ptr<int> u1 = u; error
            unique_ptr<int> u2 = move(u);
            unique_ptr<int []> u_arr(new int[10]);
            u_arr[1] = 2;
            cout << u_arr[0] << endl;
    
            weak_ptr<int> w(p);
            cout << w.use_count() << endl;
    
            if (!w.expired()) {
                    auto tmp = w.lock();
                    cout << "success " << *tmp << endl;
            }
            p.reset();
            if (w.expired()) {
                    cout << "failed" << endl;
            }
    
    
            void* h = A::Create();
            shared_ptr<void> sh(h, [](void*p) { A::Destroy(p); });
    }
    
    
    /********
     *function
     *
    *********/
    void Fun() {
    }
    
    class Obj {
    public:
            void operator()() {
            }
    };
    
    
    class Obj1 {
            using fun = void(*)();
    public:
            static void F() {
            }
            operator fun() {
                    return F;
            }
    };
    
    class Obj2 {
    public:
            void F() {
            }
    
            static int F1(int a) {
                    return a+2;
            }
    };
    
    void Ffunc() {
            void (*pf)() = &Fun;
            pf();
    
            Obj o;
            o();
    
            Obj1 o1;
            o1();
    
            void (Obj2::*mpf)() = &Obj2::F;
            Obj2 o3;
            (o3.*mpf)();
    }
    
    void Ffunc1(const function<void(void)>& f) {
            f();
    } 
    
    void Ffunc2() {
            function<void(void)> f = Fun;
            f();
    
            Obj o;
            function<void(void)> f2 = o;
            f2();
    
            function<void(void)> ff = bind(Obj());
            ff();
    
            function<int(int)> f1 = Obj2::F1;
            cout << f1(2) << endl;
    
            Obj2 o2;
            function<void(void)> f3 = bind(&Obj2::F, &o2);
            f3();
    
            Ffunc1(f);
            Ffunc1(Fun); //函数参数必须const
    }
    
    
    /********
     *bind
     *
    *********/
    void Add(int x, int y) {
            cout << x << "+" << y << endl;
    }
    
    void Fbind() {
            bind(Add, 1, 2)();
            bind(Add, placeholders::_1, 2)(1);
            bind(Add, 2, placeholders::_1)(1);
            //bind(Add, 2, placeholders::_2)(1);
            bind(Add, 2, placeholders::_2)(1, 2); //2 2
            bind(Add, placeholders::_2, placeholders::_1)(1, 2); //2 1
    }
    
    void Fbind1() {
            vector<int> v = {2, 3, 10, 12};
            cout << count_if(v.begin(), v.end(), bind1st(less<int>(), 10)) << endl;
            cout << count_if(v.begin(), v.end(), bind2nd(less<int>(), 10)) << endl;
            cout << count_if(v.begin(), v.end(), bind(less<int>(), 10, placeholders::_1)) << endl; 
            cout << count_if(v.begin(), v.end(), bind(less<int>(), placeholders::_1, 10)) << endl; 
    
            // (6, 12)
            auto f1 = bind(greater<int>(),  placeholders::_1, 6);
            auto f2 = bind(less<int>(),  placeholders::_1, 12);
            auto f3 = bind(logical_and<bool>(), f1, f2);
            cout << count_if(v.begin(), v.end(), f3) << endl;
    }
    
    int main() {
            //Fptr();
            Ffunc();
            Ffunc2();
            Fbind();
            return 0;
    }

**初始化列表**

**右值引用**

#include<iostream>
    #include<vector>
    #include<map>
    #include<unordered_map>
    #include<algorithm>
    using namespace std;
    
    
    /********
     *initializer_list
     *
    *********/
    class A {
            vector<int> v_;
    public:
            A(initializer_list<int> l) {
                    for(auto it = l.begin(); it != l.end(); ++it) {
                            v_.push_back(*it);
                    }
            }
    };
    
    class B {
            map<int, int> m_;
            using pair = map<int, int>::value_type;
    public:
            B(initializer_list<pair> l) {
                    for(auto it = l.begin(); it != l.end(); ++it) {
                            m_.insert(*it);
                    }
            }
    };
    
    void Finit() {
            A a = {1, 2, 3};
            vector<int> v = {1, 2, 3};
            B b = { {1, 2}, {3, 4}};
            int c = {1.2}; //conversion warnning
    
    }
    
    /********
     *-fno-elide-constructors
     *
    *********/
    class C {
    public:
            C() {
                    cout << "construct" << endl;
            }
    
            C(const C&) {
                    cout << "copy construct" << endl;
            }
    
            ~C() {
                    cout << "destruct" << endl;
            }
    };
    
    C GetC() {
            return C();
    }
    
    class D {
    static const int CNT = 2;
    int arr_[CNT];
    };
    int main() {
            Finit();
            //C&& c = GetC();       //减少一次拷贝构造
            //const C& c = GetC();  //减少一次拷贝构造
            auto&& c = GetC();      //减少一次拷贝构造
    
            //自动推导左or右
            auto&& c1 = c;
            auto&& d = 2;           
    
    
            return 0;
    }

**lambda**

#include<iostream>
    #include<vector>
    #include<map>
    #include<unordered_map>
    #include<algorithm>
    using namespace std;
    
    /********
     *lambda 
     *
    *********/
    class A {
    public:
            int v_ = 0;
            void F(int a, int b) {
                    //auto f1 = [] { return v_; } error
                    auto f1 = [this] { return v_; };
                    f1();
                    auto f2 = [&] { return v_; };
                    f2();
                    auto f3 = [=] { return v_; };
                    f3();
                    auto f4 = [=](int c = 3) { F1(c); };
                    f4();
                    f4(2);
    
                    auto f5 = [=]() { F1(a); };
                    auto f6 = [&]() { F1(b); };
            }
            int F1(int a) {
                    v_ = a;
            }
    
    };
    
    void Flambda() {
            auto f = [](int a) -> float { return a + 0.2; };
            cout << f(2) << endl;
    
            auto f1 = [](int a) { return a + 0.2; };
            cout << f1(3) << endl;
    
            int a = 0, b = 1;
            //auto f2 = [] { return a; }; error
            auto f2 = [a] { return a; }; //按值捕获，捕获的时候值已经复制
            a = 1;
            cout << "a=" << a << ", b=" << b << ", f2=" << f2() << endl;//f2输出？
    
            auto f2_0 = [&a] { return a; };
            a = 22;
            cout << "a=" << a << ", b=" << b << ", f2_0=" << f2_0() << endl;//引用没问题
    
            auto f3 = [&a] { a = 3; };
            f3();
    
            //auto f4 = [=,&a] { b = 10; a = 22; }; b read-only
            auto f4 = [=,&a] { a = b; }; 
            f4();
            auto f5 = [&] { a = 10; b = 11; }; 
            f5();
            cout << "a=" << a << ", b=" << b << endl;
    }
    
    void Flambda1() {
            vector<int> v = {1, 2, 6, 10};
            cout << count_if(v.begin(), v.end(), [](int x) { return (x < 10 && x > 5); }) << endl;
    }
    class B {
            int& v_;
    public:
            B(int& v) : v_(v) {
            }
            void operator()(int v) {
                    if (v & 1) {
                            v_++;
                    }
            }
    };
    
    void Flambda2() {
            vector<int> v = {1, 2, 3, 4, 5};
            int cnt = 0;
            for_each(v.begin(), v.end(), B(cnt));
            cout << cnt << endl;
    
            int cnt1 = 0;
            for_each(v.begin(), v.end(), [&cnt1](int a) { if (a & 1) cnt1++; });
            cout << cnt1 << endl;
    }
    
    struct C {
            bool operator()(int v) {
                    return true;
            }
    };
    
    
    int main() {
            //Flambda();
            Flambda2();
    
            vector<int> v = {1, 2, 3, 4, 5};
            cout << count_if(v.begin(), v.end(), C()) << endl;
            return 0;
    }