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auto.cpp
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105 lines (83 loc) · 2.57 KB
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//
// Created by light on 19-11-2.
//
#include <iostream>
#include <list>
#include <algorithm>
#include <vector>
#include <functional>
#include <iterator>
using namespace std;
// iterator stl_iterator.h里面的源码 使用auto
template<typename _Iterator>
#if __cplusplus < 201103L
inline typename reverse_iterator<_Iterator>::difference_type
operator-(const reverse_iterator<_Iterator>& __x,
const reverse_iterator<_Iterator>& __y)
#else
inline auto
operator-(const reverse_iterator<_Iterator> &__x,
const reverse_iterator<_Iterator> &__y)
-> decltype(__x.base() - __y.base())
#endif
{ return __y.base() - __x.base(); }
// auto 关键字(c++11) 语法糖
// for 循环 ranged-base for
class C {
public:
explicit C(const string &s) : mystr(s) {
}
friend ostream &operator<<(ostream out, const C &c) {
out << c.mystr << endl;
}
private:
string mystr;
};
int main() {
auto i = 42; // 编译器具备实参推导
auto ll1 = [](int x) -> int {
return x + 10;
};
// lambda 匿名函数
function<int(int x)> ll = [](int x) -> int {
return x + 10;
};
cout << ll(10) << endl;
list<int> l{1, 2, 3};
list<int>::iterator iterator;
iterator = find(l.begin(), l.end(), 10);
auto ite = find(l.begin(), l.end(), 11); // auto 关键字
vector<int> vec;
//=====================range-based for statement=========================
// (1)
for (auto elem:vec) // pass by value
cout << elem << endl;
// c++2.0 之前 (2) 编译器会把(1)转换为(2)或(3)
for (auto _pos = l.begin(), _end = l.end(); _pos != _end; ++_pos)
cout << *_pos << " ";
cout << endl;
// (3)
// c++2.0之后 全局函数begin(container)与end(container) 可以接受容器
for (auto _pos = begin(l), _end = end(l); _pos != _end; ++_pos)
cout << *_pos << " ";
cout << endl;
// (4)
for (auto &elem:vec) // pass by reference
elem *= 3;
// (5) 编译器会把(4)转换为(5)
for (auto _pos = l.begin(), _end = l.end(); _pos != _end; ++_pos) {
auto &elem = *_pos;
elem *= 3;
}
cout << endl;
vector<string> vs = {"hello", "world"};
// 加了explicit就不能转了 error
// for (const C &elem:vs) {
// }
// 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
// auto可能得不到你预想的类型，如vector<bool>[]的返回类型。
vector<bool> v(true);
auto var = v.at(0);
cout<< typeid(var).name()<<endl;
return 0;
}