C++ - 标准库

#include <string>
#include <cctype>
using std::string;

// Construction
string s1;
string s2 = "hello";
string s3(s2);

// IO
string s;
cin >> s; // read a whitespace-separated string into s
getline(cin, s); // read a whole line
cout << s << endl;

while (cin >> word) // read until EOF, can be replaced with getline
    cout << word << endl;

string s = to_string(123);
int a = stoi("123");

// Basic ops
s.empty() // py: same
s.size() // string::size_type, py: len(s)
s[i] // indexing
s1 + s2 // concatenation
s1 == s2

// Iteration
string s("Hello World!!!");
decltype(s.size()) punct_cnt = 0; // ensure the type is right
for (auto c : s)
    if (ispunct(c))
	    ++punct_cnt;

for (auto &c : s) // c is a reference!
    c = toupper(c); // <cctype>
cout << s << endl;

// Substring
s.substr(10,15); // start from 10, find next 15 characters
// s.finds returns the first index
// if fail, return string::nops
s.find('i', 0); // start from index 0
s.find("world"); // can also pass in string
s.rfind('s',string::nops); // start from the right
s.replace(0,3,"qqqq"); // delete [0,3), and insert at 0
s.insert(3,"abc");

#include <vector>
using std::vector;

// Construction
vector<int> ivec;
vector<string> v1 {"a", "ab", "abc"}; // list initialization
vector<int> v2(10,-1); // py: [-1] * 10

// Basic ops
v.push_back(1);
v.empty();
v.size();
v[i];
v1 == v2;

// Iterator
for (std::vector<int>::iterator it = s.begin(); it != s.end(); ++it)
    cout << *it << endl; // iterator is a pointer
// cbegin, cend: constant iterator

unsigned cnt = 42; // 不是常量表达式
constexpr unsigned sz = 42 ;
string bad[cnt]; // 非法
string str_s[get_size()]; // 当get_size是constexpr时正确 否则错误

int ia[3][4] = {0,1,2,3,4,5,6,7,8,9,10,11}; // 与加了内层花括号等价
int ia[3][4] = { {0},{4},{8} }; // 初始化每行首元素
int ix[3][4] = {0,3,6,9}; // 初始化第一行

size_t cnt = 0;
for (auto &row : ia)
    for (auto &col : row){
        col = cnt;
        ++cnt;
    }

for (const auto &row : ia) // 外层循环要用引用，同时避免转为指针类型
    for(auto col : row)
        cout << col << endl;

int ia[3][4];
int (*p)[4] = ia; // 括号不能少，p指向含有4个整数的数组，而不是整型指针的数组
for (auto p = begin(ia); p != end(ia); ++p)
    for (auto q = begin(*p); q != end(*p); ++q)
        cout << *q << ' ';

stack<int> stk;
stk.push(2);
stk.pop();
int top = stk.top();

priority_queue< int, vector<int>, greater<int> > q; // increase
q.push(3);
q.pop();

pair<T1, T2> p1;
pair<T1, T2> p1(v1,v2);
p1.first;
p1.second;

map<string,int> namemap;
// insert
namemap["Alice"] = 18;

// search
namemap.count("Alice") > 0
if (namemap.find("Alice") != namemap.end())
    ...

for (auto &i : name) {
	std::cout << i.first << " " << i.second << std::endl;
}

// delete
namemap.erase("Alice"); // erase by key
namemap.erase(it); // erase by iterator

set<int> s;
s.insert(1);
it = s.find(20);
s.erase(it);

// set union
#include <algorithm>
int first[] = {5,10,15,20,25};
int second[] = {50,40,30,20,10};
std::vector<int> v(10);
std::vector<int>::iterator it = std::set_union(first, first+5, second, second+5, v.begin());
// std::set_intersection is similar
v.resize(it-v.begin());

using PII = pair<int, int>;
auto hash_function = [](const PII& o) {return hash<int>()(o.first) ^ hash<int>()(o.second);};
unordered_set<PII, decltype(hash_function)> seen(0, hash_function);

ifstream in(ifile);
ofstream out;
out.open("a.out");
out.close();
ofstream out2("file1",ofstream::app) // 保留文件内容，定位到文件末尾

string line, word;
vector<PersonInfo> people;
while (getline(cin,line))
{
	PersonInfo info;
	istringstream record(line); //将记录绑定到刚读入的行
	record >> info.name;
	while (record >> word)
		info.phones.push_back(word);
	people.push_back(info);
}

ostringstream badNums;
badNums << " " << nums;
os << badNums.str() << endl;

list<string> names;
vector<const char*> oldstyle;
names = oldstyle; // 错误：容器类型不匹配
names.assign(oldstyle.cbegin(), oldstyle.cend()); // 正确：可以将const char*转为string

lst.before_begin() // 首元素之前一个元素
lst.cbefore_begin()
lst.insert_after(p,t) // p后插入，t对象，n数量
lst.insert_after(p,n,t)
lst.insert_after(p,b,e)
lst.insert_after(p,il)
emplace_after(p,args)
lst.erase_after(p)
lst.erase_after(b,e)

set<int> s;
set<int> s(v.begin(),v.end());
s.insert(k)
s.find(k) != s.end()
s.count(k)
s.lower_bound(k) // 返回迭代器，第一个关键字不小于k的元素
s.upper_bound(k)
s.equal_range(k)

#include <algorithm>
vector<int> c;
set_intersection(a.begin(),a.end(),b.begin(),b.end(),back_inserter(c));

bool compareIsbn(const Sales_data &lhs, const Sales_data &rhs)
{
    return lhs.isbn() < rhs.isbn();
}
multiset<Sales_data, decltype(compareIsbn)*> bookstore(compareIsbn); // 提供函数指针

// 管理桶接口
c.bucket_count()
c.max_bucket_count()
c.bucket_size(n)
c.bucket(k) // 关键字k在哪个桶

// 桶迭代
local_iterator
const_local_iterator
c.begin(n), c.end(n) // 桶n的迭代器
c.cbegin(n), c.cend(n)

// 哈希策略
c.load_factor // 每个桶的平均元素数量，返回float
c.max_load_factor() // 试图维护平均桶大小
c.rehash(n) // 重新存储为>n个桶
c.reserve(n) // 重新存储，使得c可以保存n个元素且不必rehash

tuple<string, vector<double>, int, list<int>>
auto item = make_tuple("fdsa", 3, 20.00); // 标准库定义
auto price = get<2>(item)/cnt;

bitset<20> bitvec2(0xbeef);
b.any(); // 是否存在置位的二进制位
b.all(); // 所有位都置位了吗
b.count(); // 置位的位数
b.flip(pos); // 也可通过~实现
b.set(pos,v);