STL-- string class basis functions

• The string class is a template class:

typedef  basic_string<char>string

• Use string class include the header file:

#include<string>

• object initialization string:

#include<iostream>
#include<string>
using namespace std;
int main()
{
	string s1("Hello");
	cout << s1 << endl;
	string s2(8,'x');      //代表s2里面有8个 x 
	cout << s2 << endl;
	string month="Match";
	cout << month << endl;
	string s;
	s='n';
	cout << s << endl;
	return 0;
}

operation result:

• Length of string objects reading function length ():

string s("Hello");
cout << s.length() << endl;

• string assignment and connection:

·用 = 赋值
    string s1("cat"), s2;
    s2 = s1;
·用 assign 成员函数复制
	string s1("cat"), s3; 
	s3.assign(s1);
·用 assign 成员函数部分复制
	string s1("catpig"), s4;
	s4.assign(s1, 1, 3);    //从s1中下标为1的字符开始复制3个字符
·单个字符复制
	s2[5] = s1[3] = 'a';
·逐个访问string对象中的字符
	string s1("Hello");
	for(int i=0;i<s1.length();i++)
		cout << s1.at(i) << endl; 
	//成员函数at会做范围检查，如果超出范围，会抛出 out_of_range异常，而下标运算符[]不做范围检查
·用 + 运算符连接字符串
	string s1("good"), s2("moring!");
	s1 += s2;
	cout << s1;
·用成员函数append连接字符串
	string s1("good"), s2("moring!");
	s1.append(s2);
	cout << s1;
	s2.append(s1, 3, s1.size());   //s1.size(), s1字符串
	cout << s2;
	//下标为3开始，s1.size()个字符，如果字符串内没有足够的字符，则复制到字符串的最后一个字符  

• Compare string:

·用关系运算符比较string的大小
	==, >, >=, <, <=, !=
	//返回值都是bool类型，成立返回true，否则返回false
	string s1("hello"), s2("hello"), s3("hell");
	bool b = (s1 == s2);
	cout << b << endl;      //运行结果为 1
	b = (s1 == s3)
	cout << b << endl;      //运行结果为 0 
	b = (s1 > s3)
	cout << b << endl;      //运行结果为 1 
·用成员函数compare比较string的大小
	string s1("hello"), s2("hello"), s3("hell");
	int f1 = s1.compare(s2);  //运行结果为 0 
	int f2 = s1.compare(s3);  //运行结果为 1 
	int f3 = s3.compare(s1);  //运行结果为 -1
	int f4 = s1.compare(1, 2, s3, 0, 3); //运行结果为 -1  
	//将s1从下标为1开始的2个字符与s3的从0开始的3个字符比较  
	int f5 = s1.compare(0, s1.size(), s3);  //运行结果为 1
	cout << f1 << endl << f2 << endl << f3 << endl;
	cout << f4 << endl << f5 << endl;
	

Implementation code as follows:

#include<iostream>
#include<string>
using namespace std;
int main()
{
	string s1("hello"), s2("hello"), s3("hell");
	bool b = (s1 == s2);
	cout << b << endl;    
	b = (s1 == s3);
	cout << b << endl; 
	b = (s1 > s3);
	cout << b << endl;      
	int f1 = s1.compare(s2); 
	int f2 = s1.compare(s3); 
	int f3 = s3.compare(s1);
	int f4 = s1.compare(1, 2, s3, 0, 3); 
	//将s1从下标为1开始的2个字符与s3的从0开始的3个字符比较  
	int f5 = s1.compare(0, s1.size(), s3);  
	cout << f1 << endl << f2 << endl << f3 << endl;
	cout << f4 << endl << f5 << endl;
	return 0;	
}

Operating results as follows:

• Substring:

·成员函数substr
	string s1("hello world"), s2;
	s2 = s1.substr(4,5);     //从下边4开始的5个字符
	cout << s2 << endl;      //运行结果为  o wor
	 

• Exchange string:

·成员函数swap
	string s1("hello world"), s2("really");
	s1.swap(s2);
	cout << s1 << endl;
	cout << s2 << endl;
	 

Operating results as follows:

• Looking string of characters:

·成员函数find()
	string s1("hello world");
	s1.find("lo");
	//在s1中从后向前查找，“lo”第一次出现的地方，如果找到，返回“lo”开始的位置，即l所在位置的下标。如果找不到，返回string::npos(string中定义的静态常量)
·成员函数rfind()
	string s1("hello world");
	s1.rfind("lo");
	//在s1中从后向前查找，“lo”第一次出现的地方，如果找到，返回“lo”开始的位置，即l所在位置的下标。如果找不到，返回string::npos(string中定义的静态常量) 
·成员函数find_first_of()
	string s1("hello world");
	s1.find_first_of("abcd");
	//在s1中从前向后查找，“abcd”中任何一个字符第一次出现的地方，如果找到，返回找到字母的位置。如果找不到，返回string::npos(string中定义的静态常量)
·成员函数find_last_of()
	string s1("hello world");
	s1.find_last_of("abcd");
	//在s1中查找，“abcd”中任何一个字符最后一次出现的地方，如果找到，返回找到字母的位置。如果找不到，返回string::npos(string中定义的静态常量)	
·成员函数find_first_not_of()
	string s1("hello world");
	s1.find_first_not_of("abcd");
	//在s1中从前向后查找不在“abcd”中的字母第一次出现的地方，如果找到，返回找到字母的位置。如果找不到，返回string::npos(string中定义的静态常量)

The code is implemented as:

#include<iostream>
#include<string>
using namespace std;
int main()
{
	string s1("hello worlld");
	cout << s1.find("ll") << endl;
	cout << s1.find("abc") << endl;
	cout << s1.rfind("ll") << endl;
	cout << s1.rfind("abc") << endl;
	cout << s1.find_first_of("abcde") << endl;
	cout << s1.find_first_of("abc") << endl;
	cout << s1.find_last_of("abcde") << endl;
	cout << s1.find_last_of("abc") << endl;
	cout << s1.find_first_not_of("abcde") << endl;
	cout << s1.find_first_not_of("hello world") << endl;
	cout << s1.find_last_not_of("abcde") << endl;
	cout << s1.find_last_not_of("hello world") << endl;
	return 0;	
}

Operating results as follows:

• Delete string of characters:

·成员函数erase()
	string s1("hello worlld");
	s1.erase(5);    //去掉下标5及以后的字符 
	cout << s1;
	cout << s1.length();
	cout << s1.size();          //运行结果为 hello55 

• Replace string of characters:

·成员函数replace()
	string s1("hello world");
	s1.replace(2,3,"haha");    //将s1中下标2开始的3个字符换成"haha" 
	cout << s1;                //运行结果为 hehaha world
	s1.replace(2,3,"haha",1,2);    //将s1中下标2开始的3个字符换成"haha" 中下标1开始的2个字符 
	cout << s1;                //运行结果为 heah world 

• Insert characters in the string:

·成员函数insert()
	string s1("hello worlld");
	string s2("show insert");
	s1.insert(5,s2);    //将s2插入s1下标5的位置 
	cout << s1 << endl; //运行结果为  helloshow insert worlld
	s1.insert(2,s2,5,3);//将s2中下标5开始的3个字符插入s1下标2的位置 
	cout << s1 << endl;//运行结果为  heinslloshow insert worlld