STL基础--String

Posted 2021-01-31 logchen

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
s1.resize(12, ‘x‘); //s1: Goodbyexxx
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"
s1.data();  // "abc" c++11中结尾也有

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);       //‘
‘
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();