以下內容大部分使用 C++11 !
以下內容大部分使用 C++11 !
以下內容大部分使用 C++11 !

通過 {} 來給容器賦值

pair<int, int> p; // ... p = make_pair(3, 4);

其實可以這樣

pair<int, int> p; // ... p = {3, 4};

對于復雜的 pair

pair<int, pair<char, long long> > p; // ... p = {3, {'a', 8ll}};

對于其他容器(vector,deque,set)

vector<int> v; v = {1, 2, 5, 2}; for (auto i: v)cout << i << ' '; cout << '\n'; // prints "1 2 5 2"deque<vector<pair<int, int>>> d; d = {{{3, 4}, {5, 6}}, {{1, 2}, {3, 4}}}; for (auto i: d) {for (auto j: i)cout << j.first << ' ' << j.second << '\n';cout << "-\n"; } // prints "3 4 // 5 6 // - // 1 2 // 3 4 // -"set<int> s; s = {4, 6, 2, 7, 4}; for (auto i: s)cout << i << ' '; cout << '\n'; // prints "2 4 6 7"list<int> l; l = {5, 6, 9, 1}; for (auto i: l)cout << i << ' '; cout << '\n'; // prints "5 6 9 1"array<int, 4> a; a = {5, 8, 9, 2}; for (auto i: a)cout << i << ' '; cout << '\n'; // prints "5 8 9 2"tuple<int, int, char> t; t = {3, 4, 'f'}; cout << get<2>(t) << '\n';

注意：stack,queue不適用

宏

通過 '#' 來得到參數名

#define what_is(x) cerr << #x << " is " << x << endl; // ... int a_variable = 376; what_is(a_variable); // prints "a_variable is 376" what_is(a_variable * 2 + 1) // prints "a_variable * 2 + 1 is 753"

使用 <bits/stdc++.h>

#include <bits/stdc++.h>

庫中自帶卻不怎么常用的函數

• __gcd(value1,value2)
  e.g. __gcd(18, 27) = 9.
• __builtin_ffs(x)
  e.g. __builtin_ffs(10) = 2 because 10 is '...10 1 0' in base 2 and first 1-bit from right is at index 1 (0-based) ’and function returns 1 + index.
• __builtin_clz(x)
  e.g. __builtin_clz(16) = 27 because 16 is ' ... 10000'. Number of bits in a unsigned int is 32. so function returns 32 — 5 = 27.
• __builtin_ctz(x)
  e.g. __builtin_ctz(16) = 4 because 16 is '...1 0000 '. Number of trailing 0-bits is 4.
• __builtin_popcount(x)
  e.g. __builtin_popcount(14) = 3 because 14 is '... 111 0' and has three 1-bits.

Note 還有其他 __bultin 函數,但是不怎么常用,cpp

變長參數函數與宏

int sum() { return 0; }template<typename... Args> int sum(int a, Args... args) { return a + sum(args...); }int main() { cout << sum(5, 7, 2, 2) + sum(3, 4); /* prints "23" */ }

不止是 int

int sum() { return 0; }template<typename T, typename... Args> T sum(T a, Args... args) { return a + sum(args...); }int main() { cout << sum(5, 7, 2, 2) + sum(3.14, 4.89); /* prints "24.03" */ }

C++14 可以用 auto sum(T a, Args... args)

使用宏

#define a_macro(args...) sum(args...)int sum() { return 0; }template<typename T, typename... Args> auto sum(T a, Args... args) { return a + sum(args...); }int main() { cout << a_macro(5, 7, 2, 2) + a_macro(3.14, 4.89); /* prints "24.03" */ }

=> debug 函數

#include <bits/stdc++.h>using namespace std;#define error(args...) { vector<string> _v = split(#args, ','); err(_v.begin(), args); }vector<string> split(const string& s, char c) {vector<string> v;stringstream ss(s);string x;while (getline(ss, x, c))v.emplace_back(x);return move(v); }void err(vector<string>::iterator it) {} template<typename T, typename... Args> void err(vector<string>::iterator it, T a, Args... args) {cerr << it -> substr((*it)[0] == ' ', it -> length()) << " = " << a << '\n';err(++it, args...); }int main() {int a = 4, b = 8, c = 9;error(a, b, c); } /* Output:a = 4b = 8c = 9 */

C++0x 與 C++

遍歷

set<int> s = {8, 2, 3, 1}; for (set<int>::iterator it = s.begin(); it != s.end(); ++it)cout << *it << ' '; // prints "1 2 3 8"

上面代碼好長呀,可以這樣

set<int> s = {8, 2, 3, 1}; for (auto it: s)cout << it << ' '; // prints "1 2 3 8"

可以用 &auto 來 替代 auto

vector<int> v = {8, 2, 3, 1}; for (auto &it: v) it *= 2; for (auto it: v) cout << it << ' '; // prints "16 4 6 2"

Power of auto

set<pair<int, pair<int, int> > >::iterator
可以這樣寫 auto it = s.begin()

for(i = 1; i <= n; i++) {for(j = 1; j <= m; j++)cout << a[i][j] << " ";cout << "\n"; }

等價于

for(i = 1; i <= n; i++)for(j = 1; j <= m; j++)cout << a[i][j] << " \n"[j == m];

tie 和 emplace_back

#define mt make_tuple #define eb emplace_back typedef tuple<int,int,int> State; // operator< definedint main(){int a,b,c;tie(a,b,c) = mt(1,2,3); // assigntie(a,b) = mt(b,a); // swap(a,b)vector<pair<int,int>> v;v.eb(a,b); // shorter and faster than pb(mp(a,b))// Dijkstrapriority_queue<State> q;q.emplace(0,src,-1);while(q.size()){int dist, node, prev;tie(dist, ode, prev) = q.top(); q.pop();dist = -dist;// ~~ find next state ~~q.emplace(-new_dist, new_node, node);} }

emplace_back 比 push_back更快，緊跟末尾比在他處快？
tie 中可以使用 ignore 來忽略值

tuple<int, int, int, char> t (3, 4, 5, 'g'); int a, b; tie(b, ignore, a, ignore) = t; cout << a << ' ' << b << '\n';/* Output:5 3 */

利用宏來循環

#define rep(i, begin, end) for (__typeof(end) i = (begin) - ((begin) > (end)); i != (end) - ((begin) > (end)); i += 1 - 2 * ((begin) > (end)))

• 不需要指明類型
• 從 begin 到 end

vector<int> v = {4, 5, 6, 4, 8}; rep(it, end(v), begin(v))cout << *it << ' '; // prints "8 4 6 5 4"

lambda function

[capture list](parameters) -> return value { body }
e.g.

auto f = [] (int a, int b) -> int { return a + b; }; cout << f(1, 2); // prints "3"

可以在 for_each,sort等 STL 中使用

vector<int> v = {3, 1, 2, 1, 8}; sort(begin(v), end(v), [] (int a, int b) { return a > b; }); for (auto i: v) cout << i << ' ';/* Output:8 3 2 1 1 */

move 的用法

使用move 來移動容器，不需要 copy

vector<int> v = {1, 2, 3, 4}; vector<int> w = move(v);cout << "v: "; for (auto i: v)cout << i << ' ';cout << "\nw: "; for (auto i: w)cout << i << ' '; /* Output:v: w: 1 2 3 4 */

C++0x Strings

Raw Strings

string s = R"(Hello, World!)"; // Stored: "Hello, World!" A raw string skips all escape characters like \n or \". e.g.string str = "Hello\tWorld\n"; string r_str = R"(Hello\tWorld\n)"; cout << str << r_str;/* Output:Hello World Hello\tWorld\n */// You can also have multiple line raw string:string r_str = R"(Dear Programmers, I'm using C++11 Regards, Swift!)"; cout << r_str;/* Output: Dear Programmer, I'm using C++11 Regards, Swift! */

Regular Expressions (regex)

** e.g.** regex r = "[a-z]+";

regex email_pattern(R"(^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$)"); // This email pattern is not totally correct! It's correct for most emails. string valid_email("swift@codeforces.com"), invalid_email("hello world");if (regex_match(valid_email, email_pattern))cout << valid_email << " is valid\n"; elsecout << valid_email << " is invalid\n";if (regex_match(invalid_email, email_pattern))cout << invalid_email << " is valid\n"; elsecout << invalid_email << " is invalid\n"; /* Output:swift@codeforces.com is valid hello world is invalid */

更多資料

戶定義數據標識 (User-defined literals)

栗子 0xA,1000ll,3.14f等等

long long operator "" _m(unsigned long long literal) {return literal; }long double operator "" _cm(unsigned long long literal) {return literal / 100.0; }long long operator "" _km(unsigned long long literal) {return literal * 1000; }int main() {// See results in meter:cout << 250_m << " meters \n"; // Prints 250 meterscout << 12_km << " meters \n"; // Prints 12000 meterscout << 421_cm << " meters \n"; // Prints 4.21 meters }

Note 需要添加下劃線_
聲明如下
[returnType] operator "" _[name]([parameters]) { [body] }
Note 參數僅能使用如下

(const char *)(unsigned long long int)(long double)(char)(wchar_t)(char16_t)(char32_t)(const char *, size_t)(const wchar_t *, size_t)(const char16_t *, size_t)(const char32_t *, size_t)

原貼
收錄整理，以備復習

轉載于:https://www.cnblogs.com/Forgenvueory/p/7352719.html

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