zhangxing
106 lines
2.6 KiB
C++
106 lines
2.6 KiB
C++
//
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// Created by light on 19-11-2.
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//
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#include <iostream>
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#include <list>
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#include <algorithm>
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#include <vector>
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#include <functional>
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#include <iterator>
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using namespace std;
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// iterator stl_iterator.h里面的源码 使用auto
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template<typename _Iterator>
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#if __cplusplus < 201103L
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inline typename reverse_iterator<_Iterator>::difference_type
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operator-(const reverse_iterator<_Iterator>& __x,
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const reverse_iterator<_Iterator>& __y)
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#else
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inline auto
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operator-(const reverse_iterator<_Iterator> &__x,
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const reverse_iterator<_Iterator> &__y)
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-> decltype(__x.base() - __y.base())
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#endif
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{ return __y.base() - __x.base(); }
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// auto 关键字(c++11) 语法糖
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// for 循环 ranged-base for
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class C {
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public:
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explicit C(const string &s) : mystr(s) {
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}
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friend ostream &operator<<(ostream out, const C &c) {
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out << c.mystr << endl;
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}
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private:
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string mystr;
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};
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int main() {
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auto i = 42; // 编译器具备实参推导
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auto ll1 = [](int x) -> int {
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return x + 10;
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};
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// lambda 匿名函数
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function<int(int x)> ll = [](int x) -> int {
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return x + 10;
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};
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cout << ll(10) << endl;
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list<int> l{1, 2, 3};
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list<int>::iterator iterator;
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iterator = find(l.begin(), l.end(), 10);
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auto ite = find(l.begin(), l.end(), 11); // auto 关键字
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vector<int> vec;
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//=====================range-based for statement=========================
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// (1)
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for (auto elem:vec) // pass by value
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cout << elem << endl;
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// c++2.0 之前 (2) 编译器会把(1)转换为(2)或(3)
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for (auto _pos = l.begin(), _end = l.end(); _pos != _end; ++_pos)
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cout << *_pos << " ";
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cout << endl;
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// (3)
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// c++2.0之后 全局函数begin(container)与end(container) 可以接受容器
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for (auto _pos = begin(l), _end = end(l); _pos != _end; ++_pos)
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cout << *_pos << " ";
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cout << endl;
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// (4)
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for (auto &elem:vec) // pass by reference
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elem *= 3;
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// (5) 编译器会把(4)转换为(5)
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for (auto _pos = l.begin(), _end = l.end(); _pos != _end; ++_pos) {
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auto &elem = *_pos;
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elem *= 3;
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}
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cout << endl;
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vector<string> vs = {"hello", "world"};
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// 加了explicit就不能转了 error
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// for (const C &elem:vs) {
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// }
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// auto 不利：降低代码可读性、可能得不到你预想的类型、配合decltype有意想不到的结果
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// auto可能得不到你预想的类型，如vector<bool>[]的返回类型。
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vector<bool> v(true);
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auto var = v.at(0);
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cout<< typeid(var).name()<<endl;
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return 0;
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}
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