String

构造

string s1("Hello");

string s2("Hello", 3); //s2: Hel

string s3(s1, 2); //s3: llo

string s4(s1, 2, 2); //s4: ll

string s5(5, 'a'); //s5: aaaaa

string s6({'a', 'b', 'c'}); //s6: abc

大小

s1="Goodbye"

s1.size(), s1.length()  //7

s1.capacity();

s1.reserve(100);

s1.reserve(5);  //s1: Goodbye, sizs()==7,capacity()>=7 不改变内容和size，只改变容量

s1.shrink_to_fit(); //改变容量到承载内容

s1.resize(9);  //s1: Goodbye\0\0

s1.resize(12, 'x'); //s1: Goodbye\0\0xxx

s1.resize(3); //s1: Goo

单元素访问

s1.at()会检查元素是否存在

s1[]不会检查

front, back, push_back, pop_back, begin, end

范围访问

string s2 = "Dragon Land";

s1.assign(s2);  // s1 = s2;

s1.assign(s2, 2, 4);  // s1: ago

s1.assign("Wisdom");

s1.assign("Wisdom", 3);  // s1: Wis

s1.assign(s2, 3);  // Error

s1.assign(3, 'x');  // s1: xxx

s1.assign({'a', 'b', 'c'});  // s1: abc

s1.append(" def");  // s1: abc def

s1.insert(2, "mountain", 4);  // s1: abmounc def

s1.replace(2, 5, s2, 3, 3);  // s1: abgon def

s1.erase(1, 4);  // s1: a def

s2.substr(2, 4);  // agon

s1 = "abc";

s1.c_str();  // "abc\0"

s1.data();  // "abc" c++11中结尾也有\0

s1.swap(s2);

成员函数算法

s1 = "abcdefg";

char buf[20];

size_t len = s1.copy(buf, 3);	//	buf:abc		len == 3

len = s1.copy(buf, 4, 2);		//	buf:cdef	len == 4

s1 = "If a job is worth doing, it's worth doing well";

size_t found = s1.find("doing");	// found == 18

found = s1.find("doing", 20);		// found == 36

found = s1.find("doing well", 0);		// found == 36

found = s1.find("doing well", 0, 5);		// found == 18

found = s1.find_first_of("doing");		// found == 6

found = s1.find_first_of("doing", 10);		// found == 13

found = s1.find_first_of("doing", 10, 1);		// found == 18

found = s1.find_last_of("doing");		// found == 40

found = s1.find_first_not_of("doing");		// found == 0

found = s1.find_last_not_of("doing");		// found == 45

s1.compare(s2);

if (s1 > s2) {}  //当size很大时，expensive

s1.compare(3, 2, s2);

string ss = s1 + s2;  //当size很大时，expensive

非成员函数

cout << s1 << endl;

cin >> s1;

getline(cin, s1);		//'\n'

getline(cin, s1, ';');	//';'

//数字转成string

s1 = to_string(8);

s1 = to_string(2.3e7);	// s1: 23000000.000000

s1 = to_string(0xa4);	// s1: 164

s1 = to_string(034);	// s1: 28

//string转数字

s1 = "190";

int i = stoi(s1);  //i == 190

s1 = "190 monkey";

size_t pos;

int i = stoi(s1, &pos);  //i == 190  pos == 3

s1 = "a monkey";

int i = stoi(s1, &pos);  // exception of invalid_argument

int i = stoi(s1, &pos, 16);  // i == 10

//stol, stod, stof, etc  以上函数只做简单string转换

//复杂格式使用stringstream

//lexical_cast()  //简单string转换

string和算法

s1 = "Variety is the spice of life.";

int num = count(s1.begin(), s1.end(), 'e');	//4

num = count_if(s1.begin(), s1.end(), [](char c) {return (c <= 'e' && c >= 'a');});  //6

s1 = "Goodness is better than beauty.";

string::iterator itr = search_n(s1.begin(), s1.begin()+20, 2, 's');	// itr -> first 's'

s1.erase(itr, itr+5);	//ss is

s1.insert(itr, 3, 'x');	//Goodnexxxss

s1.replace(itr, itr+3, 3, 'y');	//Goodneyyyis  replace substring

is_permutation(s1.begin(), s1.end(), s2.begin());	//检查s1是否是s2的排列

replace(s1.begin(), s1.end(), 'e', '');	//replace characters

transform(s1.begin(), s1.end(), s2.begin(),

          [](char c) {

              if (c < 'n')

                  return 'a';

              else

                  return 'z';

          });

s1 = "abcdefg";

rotate(s1.begin(), s1.begin()+3, s1.end());  //s1: defgabc

u16string s9;	//string char16_t

u32string s8;	//string char32_t

wstring s0;		//string wchar_t

to_wstring();