C++字符串类

Constructing a String (创建string对象)

• Create an empty string using string’s no-arg constructor (用无参构造函数创建一个空字串)

  string newString;//

• Create a string object from a string value or from an array of characters(由一个字符串常量或字符串数组创建string对象)：

string s1("Welcome");s1.append(" to C++"); //appends "to C++" to s1cout << s1 << endl;  //s1 now becomes Welcome to C++string s2("Welcome");s2.append(" to C and C++",3,2);//appends "C" to s2cout << s2 << endl;     //s2 now becomes Welcome Cstring s3("Welcome");  //appends " to C" to s3s3.append(" to C and C++",5); //s3 now becomes Welcome to Ccout << s3 << endl;string s4("Welcome"); s4.append(4,'G');   // appends "GGGG" to s4cout << s4 << endl; // s4 now becomes WelcomeGGGG

【Assigning a String(为字符串赋值)】【assign】
You can use several overload functions to assign new contents to a string

string s1("Welcome");s1.assign("Dallas"); // assigns "Dallas" to s1cout << s1 << endl;  // s1 now becomes Dallasstring s2 ("Welcome");s2.assign("Dallas,Texas",1,3); //assign "all" to s2cout << s2 << endl; //s2 now become allstring s3("Welcome");s3.assign("Dallas,Texas",6); // assigns "Dallas" to s3cout << s3 << endl; //s3 now become Dallasstring s4("Welcome");s4.assign(4,'G'); //assigns "GGGG" to s4cout << s4 << endl; //s4 now becomes GGGG

【Functions at，clear，erase，and empty】

• at(index) : 返回当前字符串中index位置的字符
• clear( ): 清空字符串
• erase(index,n);删除字符串从index开始的n个字符
• empty( ):检测字符串是否为空

string s1("Welcome");cout << s1.at(3) << endl; // s1.at(3) return ccout << s1.erase(2,3) << endl; //s1 is now Wemes1.clear(); // s1 is now emptycout << s1.empty() << endl; // s1.empty returns 1(means true)                            //不特别指定的话不会输出bool值，而是输出1！！！

【Comparing Strings(比较字符串)】【compare】

string s1("Welcome");string s2("Welcomg");cout << s1.compare(s2) << endl;         //s1-s2 return -2cout << s2.compare(s1) << endl;         //return 2cout << s1.compare("Welcome") << endl;  // return 0

【Obtaining Substrings(获取子串)】
【at( )函数用于获取一个单独的字符；而substr( )函数则可以获取一个子串】

string s1("Welcome");cout << s1.substr(0,1) << endl; //return W; 从0号位置开始的1位字符cout << s1.substr(3) << endl;   //return come 从3号位置开始直到结尾cout << s1.substr(3,3) << endl; //return com 从3号位置开始的3个字符

【Searching in a String(搜索字符串)】
【find( )函数可以从一个字符串中搜索一个子串或者一个字符】

string s1("Welcome to HTML");cout << s1.find("co") << endl;  //returns 3; 返回子串出现的第一个位置cout << s1.find("co".6) << endl; //returns -1 （-1表示不存在）                                 //从6号位置开始查找子串出现的第一个位置cout << s1.find('o') << endl; // returns 4 返回字符出现的第一个位置cout << s1.find('o',6) << endl; //returns 9 从6号位置开始查找字符出现的第一个位置

【Inserting and Replacing Strings(插入和替换字符串)】
【insert( ):将某个字符/字符串插入到当前字符串的某个位置】
【replace( ):将本字符串从某个位置开始的一些字符替换为其他内容】

string s1("Welcome to HTML");//W e l c o m e _ t o _  H  T  M  L \0                             //0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15s1.insert(11,"C++ and ");cout << s1 << endl; //s1 becomes Welcome to C++ and HTMLstring s2("AA");s2.insert(1,4,'B'); //在一号位置处连续插入4个相同字符cout << s2 << endl; //s2 becomes to ABBBBAstring s3("Welcome to HTML");s3.replace(11,4,"C++"); //从11号位置开始向后的4个字符替换掉，注意'\0'cout << s3 << endl;     //returns Welcome to C++

【字符串的运算符 String Operators】
Operator Description

[]                          //用数组下标运算符访问字符串中的字符=                           //将一个字符串的内容复制到另一个字符串+                           //连续两个字符串得到一个新串+=                          //将一个字符串追加到另一个字符串末尾<<                          //讲一个字符串插入一个流>>                          //从一个流提取一个字符串，分解符为空格或者空结束符==,!=,<                     //用于字符串比较（前一个ASCⅡ减后一个）<=,>,>=string s1 = "ABC";            // The = operatorstring s2 = s1;               // The = operatorfor(int i = s2.size() - 1;i >= 0;i--)    cout << s2[i];            // The [] operatorstring s3 = s1 + "DEFG";      // The + operatorcout << s3 << endl;           //s3 becomes ABCDEFGs1+= "ABC";                   cout << s1 << endl;           //s1 becomes ABCABCs1 = "ABC";s2 = "ABE";cout << (s1 == s2) << endl;   //Diaplays 0cout << (s1 != s2) << endl;   //Displays 1cout << (s1  > s2) << endl;   //Displays 0 cout << (s1 >= s2) << endl;   //Displays 0cout << (s1  < s2) << endl;   //Dispalys 1cout << (s1 <= s2) << endl;   //Dispalys 1