《探索现代化C++》泛读笔记摘要13

Chapter 4 C++库

容器

C++11

#include <iostream>
#include <vector>
#include <algorithm>
 
int main() 
{
    using namespace std;
    vector<int> v = {3,4,7,9};
    auto it = find(v.begin(),v.end(),4);
    cout<<"After "<<*it<<" comes "<<*(it+1)<<'\n';
    auto it2= v.insert(it+1, 5); // insert value 5 at pos. 2
    v.erase(v.begin()); // delete entry at pos. 1
    cout ≪ "Size = " << v.size() << ", capacity = "
    << v.capacity() << '\n';
    v.shrink_to_fit(); // drop extra entries
    v.push_back(7);
    for (auto i : v)
        cout ≪ i ≪ ",";
    cout ≪ '\n';
}

C++11 emplace系列，如emplace_back，emplace_front。

vector<matrix> v;
v.push_back(matrix(3,7));
v.emplace_back(7,9);// 相比上面节省了拷贝或者移动构造的内存操作

常见容器vector，deque，list，forward_list，set，multiset，map，multimap，unordered_map( Hash Tables)

C++20 set 方法contains

set<int> s = {1,3,4,7,9};
for (int i= 0; i < 6; ++i)
    cout << i << "is" << (s.contains(i) ? "" : "n't")
    << " contained in s.\n";

算法

算法主要定义在<algorithm>中，以及用于数字计算的<numeric>。

非修改型序列操作

find

1 2	`vector<int> seq` `=` `{3,4,7,9,2,5,7,8};` `auto it` `=` `find(begin(seq),end(seq),7);`

find_if

bool check(int i) { return i>4&&i<7;}
int main() 
{
    list<int> seq={3,4,5,7,8,9,2,8};
    auto it = find_if(begin(seq),end(seq),check);
    cout << "The first value in range is " << *it << '\n';
}

C++11 充分利用Lambda

1	`auto it` `=` `find_if(begin(seq),end(seq),[](int` `i){` `return` `i>4&&i<7;}};`

修改型序列操作

copy

vector<int> seq={3,4,7,9,2,5,7,8},v;
v.resize(seq.size());
copy(begin(seq),end(seq),begin(v));

unique函数用于移除序列中的重复项。

std::vector<int> seq= {3, 4, 7, 9, 2, 5, 7, 8, 3, 4, 3, 9};
sort(begin(seq), end(seq));
auto it= unique(begin(seq), end(seq));
resize(distance(begin(seq), it));

排序操作

1 2	`vector<int> seq=` `{3,` `4,` `7,` `9,` `2,` `5,` `7,` `8,` `3,` `4,` `3,` `9};` `sort(begin(seq), end(seq), [](int` `x,` `int` `y){return` `x > y;});`

数值操作

vector<float> v= {3.1, 4.2, 7, 9.3, 2, 5, 7, 8, 3, 4},
w(10), x(10), y(10);
iota(begin(w), end(w), 12.1);
partial_sum(begin (v), end(v), begin(x));
adjacent_difference(begin(v), end(v), begin(y));
float alpha= inner_product(begin(w), end(w), begin(v), 0.0f);
float sum_w= accumulate(begin(w), end(w), 0.0f),
product_w= accumulate(begin(w), end(w), 1.0f,
[](float x, float y){
return x*y;
});