Understand the structure and use of string containers in C++ in one article

string container

Basic string concept

nature:

string is a C++-style string. Unlike the C language char*, it is essentially a class.

The difference between string and char*:

char* is a pointer

string is a class that encapsulates char* to manage strings inside, and is a char& type container

Features:

Strit class encapsulates many member methods internally

For example: find, copy copy, delete delete, replace replace, insert insert

string manages the memory allocated by char*, and does not need to consider issues such as assignment and value cross-border. It is responsible for the class internally.

string constructor

Four function prototypes

• string() creates an empty string
• string(const char*s) is initialized using string s
• string(const string& str) uses a string object to initialize another string object
• string(int n, char c) is initialized with n characters c

Example of usage:

//String's constructorvoid test1()
{
    string s1;//Default construct    const char* str = "Leaves fall, autumn white";
    string s2(str);
    cout << "s2："<<s2 << endl;
    string s3(s2);
    cout << "s3" << s3 << endl;
    string s4(6,'a');
}

The above is an example corresponding to the four construction methods. The first method is used frequently. The second method is to set an immutable character array to initialize it. The third method is to call a copy structure. The fourth method is more interesting. The meaning in the above code is to use 6 'a' to initialize the string. The result of inputting s4 is: aaaaaa.

string assignment operation

Assign value to string string

Function prototype for assignment:

• string& operator = (const char* s)char* type string Assign to the current string
• string& operator = (const string &s) Assign string s to the current string
• string& operator = (char c) Assign character to the current string
• string& assign(const char* s) assigns string s to the current string
• string& assign(const char*s,int n) assign the current n characters of string s to the current string
• string& assign(const string &s) assign string s to the current string
• string& assign(int n, char c) assigns n characters c to the current string

Example of usage:

void test2()
{
	string str1;
	str1 = "The leaves fall in autumn white";
	cout << "str1=" << str1 << endl;

	string str2;
	str2 = str1;
	cout << "str2=" << str2 << endl;
	
	string str3;
	str3 = 'c';
	cout << "str3=" << str3 << endl;

	string str4;
	("hello c++");
	cout << "str4=" << str4 << endl;

	string str5;
	("hello c#",5);
	cout << "str5=" << str5 << endl;
	
	string str6;
	(str5);
	cout << "str6=" << str6 << endl;

	string str7;
	(6, 'w');
	cout << "str7=" << str7 << endl;
}

Tips:stirng assignment methods are many, but the overloaded operator= method is most commonly used.

string splicing operation

Stitching string at the end of the string

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) concatenate string s to the end of the current string
• string& append(const char* s, int n) concatenate 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) Connect n characters in string s starting from pos to the end of the string

Example of usage:

void test3()
{
	string str1 = "red beans";
	str1 += "Remembering Love";
	cout << "str1=" << str1<< endl;

	str1 += '?';
	cout << "str1=" << str1 << endl;

	string str2 = "yyds";
	str1 += str2;
	cout << "str1=" << str1 << endl;

	string str3 = "You";
	("low");
	cout << "str3=" << str3 << endl;

	("wuwuwu qaq", 4);
	cout << "str3=" << str3 << endl;

	(str2);
	cout << "str3=" << str3 << endl;

	(str2, 0, 1);
	cout << "str3=" << str3 << endl;
}

Tips: Beginners only need to remember a few splicing functions

string search replacement

Specify location to find string

Delete string at specified location

Function prototype:

1. Find the first occurrence of s, and start looking at pos

int find(const string& str, int pos = 0) const;
int find(const char* s , int pos ==0) const;

2. Find the first n characters of s from the pos position

int find( const char* s, int pos, int n) const;

3. Find the first occurrence location of character c

int find(const char c, int pos = e) const;

4. Find the last location of str, start from pos

int rfind(const string& str, int pos = npos) const;

5. Find the last position of str, start from pos, and count always starts from front to back

int rfind(const char* s, int pos = npos) const;

6. Find the last position of the first n characters of s from pos

int rfind(const char* s, int pos， int n) const;

7. Find the last occurrence of character c

int rfind(const char c, int pos - e) const;

8. Replace n characters starting from pos as string str

string& replace(int pos, int n, const string& str);

9. Replace n characters starting from pos as string s

string& replace(int pos， int n,const char* s );

Example of usage:

//Search and replacement of strings//Findvoid test4()
{
	string str1 = "abcdefgh";
	//Return subscript is found, return -1 cannot be found	int pos1 = ("def");
	cout << "pos1=" << pos1 << endl;
	int pos2 = ("s");
	cout << "pos2=" << pos2<< endl;

	pos1 = ("ab");//Finish the first appearance from right to left and count from left to right	cout << "pos1=" << pos1 << endl;;
}
//replacevoid test5()
{
	string str2 = "abcdef";
	(1, 2, "1111");//From the position 1, 2 characters are replaced by 1111	cout << "str2=" << str2 << endl;
}

tips:

Find find the string and returns the first character position found, and return 1 if it cannot be found.

Although there are many functions, almost all of them are in two versions, one is in the C++ style and the other is in the C language style.

string string comparison

String comparison is based on ASCII code of characters

Function prototype:

int compare(const string &s) const;
int compare(const char* s) const;

Example of usage:

string str1 = “zello”;
string str2 = “hello”;
if ((str2) == 0)
{
cout << “equal” << endl;
}
else if ((str2) > 0)
{
cout << “str1big” << endl;
}
else
{
cout << “str2big” << endl;
}

tips: The purpose of string comparison is to compare whether two strings are equal, and the meaning of judging who is bigger and who is smaller is not very important.

string character reading

There are two ways to access a single character:

Function prototype:

char& operator[] (int n); //Get characters through []char& at (int n); //Get characters through the at method

Example of usage:

string str1 = “hello”;
//Accessing a single character through []for (int i = 0; i < (); i++)
{
cout << str1[i] << " ";
}
cout << endl;
//Single character accessed through atfor (int i = 0; i < (); i++)
{
cout << (i) << " ";
}
cout << endl;
//Modify single characterstr1[0] = ‘z';
cout << str1 << endl;
(0) = ‘x';
cout << str1 << endl;

string insertion and deletion

Function prototype:

string& insert(int pos,const cahr* s);//Insert string at n positionstring& insert(int pos,const string& s);//Insert string at n positionstring& insert(int pos,int n,char c);//Insert n characters c at the specified positionstring& erase(int pos,int n = npos);//Delete n characters starting from the pos position

Example of usage:

string str = “hello”;
//insert(1, “111”);
cout << "str = " << str << endl;
//delete(1,3);
cout << "str = " << str << endl;

tips: The starting subscripts for insertion and deletion start from 0.

string seeking child string

Get the desired substring from the string

Function prototype:

string substr(int pos=0,int n=npos) const ;//Returns a string composed of n characters starting from the pos position

//StringSearch for child stringvoid test01()
{
    string str = "abcdef";
    string subStr = (1, 3);
    cout << "subStr=" << subStr << endl;
}
//Usage operationvoid test02()
{
    string email = "ylqb@";
    //Get username information from email address    int pos = ("@");
    string usrName = (0, pos);
    cout << usrName << endl;
}

tips: Flexible use of the substring function, you can obtain effective information in actual development, and you can effectively obtain user names in different mailboxes in the above code.

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