3. string container
3.1 basic concept of string
Essence:
- String is a C + + style string, and string is essentially a class
*The difference between string and char:**
- char * is a pointer
- String is a class. Char * is enclosed inside the class. It is a container of char * type to manage this string
3.2. string constructor
#include <iostream>
using namespace std;
//string constructor
/*
* string() ; //Create an empty string
* string(const char* s); //Initialize with string s
* string(const string& str) ; //Initializes a string object with a string object
* string(int n, char c); //Initialize with n characters c
*/
int main()
{
string s1; //Default construction
const char* str = "Hello !";
string s2(str);
cout << "s2 = " << s2 << endl;
string s3(s2);
cout << "s3 = " << s3 << endl;
string s4(10,'c');
cout << "s4 = " << s4 << endl;
return 0;
}
3.3. string assignment
Function prototype assigned:
- string& operator=(const char* s); // Char * type string is assigned to the current string
- string& operator=(const string &s); // Assign the string s to the current string
- string& operator=(char c); // The character is assigned to the current string
- string& assign(const char *s); // Assign the string s to the current string
- string& assign(const char *s, int n); // Assign the first n characters of string s to the current string
- string& assign(const string &s); // Assign the string s to the current string
- string& assign(int n, char c); // Assign n characters C to the current string
#include <iostream>
using namespace std;
//string assignment operation
/*
* Function prototype assigned:
string& operator=(const char* s); //char*The type string is assigned to the current string
string& operator=(const string &s); //Assign the string s to the current string
string& operator=(char c); //The character is assigned to the current string
string& assign(const char *s); //Assign the string s to the current string
string& assign(const char *s, int n); //Assign the first n characters of string s to the current string
string& assign(const string &s); //Assign the string s to the current string
string& assign(int n, char c); //Assign n characters c to the current string
*/
int main()
{
string str1;
str1 = "hello HH";
cout << "str1 = " << str1 << endl;
string str2;
str2 = str1;
cout << "str2 = " << str2 << endl;
string str3;
str3 = 'a';
cout << "str3 = " << str3 << endl;
string str4;
str4.assign("Hello af");
cout << "str4 = " << str4 << endl;
string str5;
str5.assign("heelj",2);
cout << "str5 = " << str5 << endl;
string str6;
str6.assign(str5);
cout << "str6 = " << str6 << endl;
string str7;
str7.assign(10,'c');
cout << "str7 = " << str7 << endl;
return 0;
}
3.4 string splicing
Function prototype:
- string& operator+=(const char* str); // Overload + = operator
- string& operator+=(const char c); // Overload + = operator
- string& operator+=(const string& str); // Overload + = operator
- string& append(const char *s); // Connects the string s to the end of the current string
- string& append(const char *s, int n); // Connect the first n characters of string s to the end of the current string
- string& append(const string &s); // Same as operator + = (const string & STR)
- string& append(const string &s, int pos, int n);// N characters from POS in string s are connected to the end of the string
#include <iostream>
using namespace std;
/*
* **Function prototype:**
- `string& operator+=(const char* str);` //Overload + = operator
- `string& operator+=(const char c);` //Overload + = operator
- `string& operator+=(const string& str);` //Overload + = operator
- `string& append(const char *s);` //Connects the string s to the end of the current string
- `string& append(const char *s, int n);` //Connect the first n characters of string s to the end of the current string
- `string& append(const string &s);` //Same as operator + = (const string & STR)
- `string& append(const string &s, int pos, int n);`//n characters from pos in string s are connected to the end of the string
*/
int main()
{
//String splicing
string str1 = "I";
str1 += "Love reading";
cout << "str1 = " << str1 << endl;
str1 += ':';
cout << "str1 = " << str1 << endl;
string str2 = "BOOK";
str1 += str2;
cout << "str1 = " << str1 << endl;
string str3 = "I";
str3.append(" Love");
cout << "str3 = " << str3 << endl;
str3.append(" and Game",4);
cout << "str3 = " << str3 << endl;
//Intercept from subscript 5 to subscript 9
str3.append(" and Game" , 5,9);
cout << "str3 = " << str3 << endl;
return 0;
}
3.5. string search and replacement
Function Description:
- Find: finds whether the specified string exists
- Replace: replaces the string at the specified location
Function prototype:
- int find(const string& str, int pos = 0) const; // Find the location where STR first appears, starting from POS
- int find(const char* s, int pos = 0) const; // Find the location where s first appears, starting from POS
- int find(const char* s, int pos, int n) const; // Find the first position of the first n characters of s from the POS position
- int find(const char c, int pos = 0) const; // Find where the character c first appears
- int rfind(const string& str, int pos = npos) const; // Find the last position of STR, starting from POS
- int rfind(const char* s, int pos = npos) const; // Find the location of the last occurrence of S, starting from POS
- int rfind(const char* s, int pos, int n) const; // Find the last position of the first n characters of s from POS
- int rfind(const char c, int pos = 0) const; // Find where the character c last appeared
- string& replace(int pos, int n, const string& str); // Replace n characters starting from POS with string str
- string& replace(int pos, int n,const char* s); // Replace the n characters starting from POS with the string s
be careful:
- find is from left to back, and rfind is from right to left
- find returns the first character position after finding the string. If it is not found, it returns - 1
- When replacing, you need to specify where to start, how many characters to replace and what kind of string to replace
#include <iostream>
using namespace std;
int main()
{
//Find and replace
string str1 = "abcdefgde";
int pos = str1.find("dec");
//Search from left to right. The first index to be found. If it cannot be found, it returns - 1
cout << "pos = " << pos << endl;
if (pos == -1)
{
cout << "not found" << endl;
}
else
{
cout << "pos = " << pos << endl;
}
pos = str1.rfind("de");
//rfing is looking from right to left
cout << "pos = " << pos << endl;
//replace
string str2 = "abcdefgde";
//Replace the position of subscript from 0 to 3 with HHH
str2.replace(0,3 , "HHHHH");
cout << "str2 = " << str2 << endl;
return 0;
}
3.6. string comparison
Function Description:
- Comparison between strings
Comparison method:
- String comparison is based on the ASCII code of characters
=Return 0
>Return 1
< return - 1
Function prototype:
-
int compare(const string &s) const; // Compare with string s
-
int compare(const char *s) const; // Compare with string s
#include <iostream> using namespace std; int main() { //string comparison string s1 = "hello"; string s2 = "zello"; int ret = s1.compare(s2); if(ret == 0) { cout << "s1 == s2" << endl; } else if(ret > 0) { cout << "s1 > s2" << endl; }else { cout << "s1 < s2 " << endl; } return 0; }
3.7 string character access
There are two ways to access a single character in a string
- char& operator[](int n); // Take characters by []
- char& at(int n); // Get characters through the at method
#include <iostream>
using namespace std;
int main()
{
//Character access
string str = "hello world";
//Accessed via []
for(int i = 0 ; i < str.size() ; i++)
{
cout << str[i] << " " ;
}
cout << endl;
//Access via at()
for(int i = 0 ; i < str.size() ; i++)
{
cout << str.at(i) << " ";
}
cout << endl;
//Character modification
str[0] = 'Z';
str.at(1) = 'Z';
cout << "After character modification str = " << str << endl;
return 0;
}
3.1.8 string insertion and deletion
Function Description:
- Insert and delete characters from a string
Function prototype:
- string& insert(int pos, const char* s); // Insert string
- string& insert(int pos, const string& str); // Insert string
- string& insert(int pos, int n, char c); // Inserts n characters C at the specified position
- string& erase(int Pos, int n = npos); // Delete n characters starting from Pos
#include <iostream>
using namespace std;
int main()
{
//String insertion and deletion
string str = "hello";
str.insert(1, "222");
cout << str << endl;
//[0,1)
str.insert(0,1,'C');
cout << str << endl;
//Delete [0,4)
str.erase(0,4);
cout << "Deleted str = " << str << endl;
return 0;
}
3.9 string substring
Function Description:
- Get the desired substring from the string
Function prototype:
- string substr(int pos = 0, int n = npos) const; // Returns a string of n characters starting with POS
#include <iostream>
using namespace std;
int main()
{
//Substring interception
string str = "abcdefg";
string subStr = str.substr(0,3);
cout << "intercept[0,4) = " << subStr << endl;
string email = "hello@sina.com";
//Found subscript for @
int pos = email.find("@");
//String up to @
string username = email.substr(0 , pos);
cout << "username = " << username << endl;
return 0;
}