How to create a custom String class in C++ with basic functionalities
Last Updated :
01 Feb, 2022
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In this article, we will create our custom string class which will have the same functionality as the existing string class.
The string class has the following basic functionalities:
- Constructor with no arguments: This allocates the storage for the string object in the heap and assign the value as a NULL character.
- Constructor with only one argument : It accepts a pointer to a character or we can say if we pass an array of characters, accepts the pointer to the first character in the array then the constructor of the String class allocates the storage on the heap memory of the same size as of the passed array and copies the contents of the array to that allocated memory in heap. It copies the contents using the strcpy() function declared in cstring library.
Before doing the above operation it checks that if the argument passed is a NULL pointer then it behaves as a constructor with no arguments. - Copy Constructor: It is called when any object created of the same type from an already created object then it performs a deep copy. It allocates new space on the heap for the object that is to be created and copies the contents of the passed object(that is passed as a reference).
- Move Constructor: It is typically called when an object is initialized(by direct-initialization or copy-initialization) from rvalue of the same type. It accepts a reference to an rvalue of an object of the type of custom string class.
Below is the implementation of the above methods using custom string class Mystring:
// C++ program to illustrate the
// above discussed functionality
#include <cstring>
#include <iostream>
using namespace std;
// Custom string class
class Mystring {
// Initialise the char array
char* str;
public:
// No arguments Constructor
Mystring();
// Constructor with 1 arguments
Mystring(char* val);
// Copy Constructor
Mystring(const Mystring& source);
// Move Constructor
Mystring(Mystring&& source);
// Destructor
~Mystring() { delete str; }
};
// Function to illustrate Constructor
// with no arguments
Mystring::Mystring()
: str{ nullptr }
{
str = new char[1];
str[0] = '\0';
}
// Function to illustrate Constructor
// with one arguments
Mystring::Mystring(char* val)
{
if (val == nullptr) {
str = new char[1];
str[0] = '\0';
}
else {
str = new char[strlen(val) + 1];
// Copy character of val[]
// using strcpy
strcpy(str, val);
str[strlen(val)] = '\0';
cout << "The string passed is: "
<< str << endl;
}
}
// Function to illustrate
// Copy Constructor
Mystring::Mystring(const Mystring& source)
{
str = new char[strlen(source.str) + 1];
strcpy(str, source.str);
str[strlen(source.str)] = '\0';
}
// Function to illustrate
// Move Constructor
Mystring::Mystring(Mystring&& source)
{
str = source.str;
source.str = nullptr;
}
// Driver Code
int main()
{
// Constructor with no arguments
Mystring a;
// Convert string literal to
// char array
char temp[] = "Hello";
// Constructor with one argument
Mystring b{ temp };
// Copy constructor
Mystring c{ a };
char temp1[] = "World";
// One arg constructor called,
// then the move constructor
Mystring d{ Mystring{ temp } };
return 0;
}
// C++ program to illustrate the// above discussed functionalityusing namespace std;// Custom string classclass Mystring { // Initialise the char array char* str;public: // No arguments Constructor Mystring(); // Constructor with 1 arguments Mystring(char* val); // Copy Constructor Mystring(const Mystring& source); // Move Constructor Mystring(Mystring&& source); // Destructor ~Mystring() { delete str; }};// Function to illustrate Constructor// with no argumentsMystring::Mystring() : str{ nullptr }{ str = new char[1]; str[0] = '\0';}// Function to illustrate Constructor// with one argumentsMystring::Mystring(char* val){ if (val == nullptr) { str = new char[1]; str[0] = '\0'; } else { str = new char[strlen(val) + 1]; // Copy character of val[] // using strcpy strcpy(str, val); str[strlen(val)] = '\0'; cout << "The string passed is: " << str << endl; }}// Function to illustrate// Copy ConstructorMystring::Mystring(const Mystring& source){ str = new char[strlen(source.str) + 1]; strcpy(str, source.str); str[strlen(source.str)] = '\0';}// Function to illustrate// Move ConstructorMystring::Mystring(Mystring&& source){ str = source.str; source.str = nullptr;}// Driver Codeint main(){ // Constructor with no arguments Mystring a; // Convert string literal to // char array char temp[] = "Hello"; // Constructor with one argument Mystring b{ temp }; // Copy constructor Mystring c{ a }; char temp1[] = "World"; // One arg constructor called, // then the move constructor Mystring d{ Mystring{ temp } }; return 0;}Output:
The string passed is: Hello The string passed is: Hello
Some more functionalities of string class:
- pop_back(): Removes the last element from the Mystring object.
- push_back(char ch): Accepts a character as an argument and adds it to the end of the Mystring object.
- length(): Returns the length of the mystring.
- copy(): It copies the mystring object to a character array from a given position(pos) and a specific length(len).
- swap(): It swaps the two Mystring objects.
- Concatenate two strings using overloading the '+' operator: Allows us to concatenate two strings.
Below is the program to illustrate the above-discussed functionality:
// C++ program to illustrate the
// above functionalities
#include <cstring>
#include <iostream>
using namespace std;
// Class Mystring
class Mystring {
// Prototype for stream insertion
friend ostream&
operator<<(
ostream& os,
const Mystring& obj);
// Prototype for stream extraction
friend istream& operator>>(
istream& is,
Mystring& obj);
// Prototype for '+'
// operator overloading
friend Mystring operator+(
const Mystring& lhs,
const Mystring& rhs);
char* str;
public:
// No arguments constructor
Mystring();
// pop_back() function
void pop_bk();
// push_back() function
void push_bk(char a);
// To get the length
int get_length();
// Function to copy the string
// of length len from position pos
void copy(char s[], int len, int pos);
// Swap strings function
void swp(Mystring& rhs);
// Constructor with 1 arguments
Mystring(char* val);
// Copy Constructor
Mystring(const Mystring& source);
// Move Constructor
Mystring(Mystring&& source);
// Overloading the assignment
// operator
Mystring& operator=(
const Mystring& rhs);
// Destructor
~Mystring() { delete str; }
};
// Overloading the assignment operator
Mystring& Mystring::operator=(
const Mystring& rhs)
{
if (this == &rhs)
return *this;
delete[] str;
str = new char[strlen(rhs.str) + 1];
strcpy(str, rhs.str);
return *this;
}
// Overloading the plus operator
Mystring operator+(const Mystring& lhs,
const Mystring& rhs)
{
int length = strlen(lhs.str)
+ strlen(rhs.str);
char* buff = new char[length + 1];
// Copy the strings to buff[]
strcpy(buff, lhs.str);
strcat(buff, rhs.str);
buff[length] = '\0';
// String temp
Mystring temp{ buff };
// delete the buff[]
delete[] buff;
// Return the concatenated string
return temp;
}
// Overloading the stream
// extraction operator
istream& operator>>(istream& is,
Mystring& obj)
{
char* buff = new char[1000];
memset(&buff[0], 0, sizeof(buff));
is >> buff;
obj = Mystring{ buff };
delete[] buff;
return is;
}
// Overloading the stream
// insertion operator
ostream& operator<<(ostream& os,
const Mystring& obj)
{
os << obj.str;
return os;
}
// Function for swapping string
void Mystring::swp(Mystring& rhs)
{
Mystring temp{ rhs };
rhs = *this;
*this = temp;
}
// Function to copy the string
void Mystring::copy(char s[], int len,
int pos)
{
for (int i = 0; i < len; i++) {
s[i] = str[pos + i];
}
s[len] = '\0';
}
// Function to implement push_bk
void Mystring::push_bk(char a)
{
// Find length of string
int length = strlen(str);
char* buff = new char[length + 2];
// Copy character from str
// to buff[]
for (int i = 0; i < length; i++) {
buff[i] = str[i];
}
buff[length] = a;
buff[length + 1] = '\0';
// Assign the new string with
// char a to string str
*this = Mystring{ buff };
// Delete the temp buff[]
delete[] buff;
}
// Function to implement pop_bk
void Mystring::pop_bk()
{
int length = strlen(str);
char* buff = new char[length];
// Copy character from str
// to buff[]
for (int i = 0; i < length - 1; i++)
buff[i] = str[i];
buff[length-1] = '\0';
// Assign the new string with
// char a to string str
*this = Mystring{ buff };
// delete the buff[]
delete[] buff;
}
// Function to implement get_length
int Mystring::get_length()
{
return strlen(str);
}
// Function to illustrate Constructor
// with no arguments
Mystring::Mystring()
: str{ nullptr }
{
str = new char[1];
str[0] = '\0';
}
// Function to illustrate Constructor
// with one arguments
Mystring::Mystring(char* val)
{
if (val == nullptr) {
str = new char[1];
str[0] = '\0';
}
else {
str = new char[strlen(val) + 1];
// Copy character of val[]
// using strcpy
strcpy(str, val);
str[strlen(val)] = '\0';
}
}
// Function to illustrate
// Copy Constructor
Mystring::Mystring(const Mystring& source)
{
str = new char[strlen(source.str) + 1];
strcpy(str, source.str);
}
// Function to illustrate
// Move Constructor
Mystring::Mystring(Mystring&& source)
{
str = source.str;
source.str = nullptr;
}
// Driver Code
int main()
{
// Constructor with no arguments
Mystring a;
// Convert string literal to
// char array
char temp[] = "Hello";
// Constructor with one argument
Mystring b{ temp };
// Copy constructor
Mystring c{ a };
char temp1[] = "World";
// One arg constructor called,
// then the move constructor
Mystring d{ Mystring{ temp } };
// Remove last character from
// Mystring b
b.pop_bk();
// Print string b
cout << "Mystring b: "
<< b << endl;
// Append last character from
// Mystring b
b.push_bk('o');
// Print string b
cout << "Mystring b: "
<< b << endl;
// Print length of string b
cout << "Length of Mystring b: "
<< b << endl;
char arr[80];
// Copy string b chars from
// length 0 to 3
b.cpy(arr, 3, 0);
// Print string arr
cout << "arr is: "
<< arr << endl;
// Swap d and b
d.swp(b);
// Print d and b
cout << d << " "
<< b << endl;
// Concatenate b and b with
// overloading '+' operator
d = b + b;
// Print string d
cout << "string d: "
<< d << endl;
return 0;
}
// C++ program to illustrate the// above functionalitiesusing namespace std;// Class Mystringclass Mystring { // Prototype for stream insertion friend ostream& operator<<( ostream& os, const Mystring& obj); // Prototype for stream extraction friend istream& operator>>( istream& is, Mystring& obj); // Prototype for '+' // operator overloading friend Mystring operator+( const Mystring& lhs, const Mystring& rhs); char* str;public: // No arguments constructor Mystring(); // pop_back() function void pop_bk(); // push_back() function void push_bk(char a); // To get the length int get_length(); // Function to copy the string // of length len from position pos void copy(char s[], int len, int pos); // Swap strings function void swp(Mystring& rhs); // Constructor with 1 arguments Mystring(char* val); // Copy Constructor Mystring(const Mystring& source); // Move Constructor Mystring(Mystring&& source); // Overloading the assignment // operator Mystring& operator=( const Mystring& rhs); // Destructor ~Mystring() { delete str; }};// Overloading the assignment operatorMystring& Mystring::operator=( const Mystring& rhs){ if (this == &rhs) return *this; delete[] str; str = new char[strlen(rhs.str) + 1]; strcpy(str, rhs.str); return *this;}// Overloading the plus operatorMystring operator+(const Mystring& lhs, const Mystring& rhs){ int length = strlen(lhs.str) + strlen(rhs.str); char* buff = new char[length + 1]; // Copy the strings to buff[] strcpy(buff, lhs.str); strcat(buff, rhs.str); buff[length] = '\0'; // String temp Mystring temp{ buff }; // delete the buff[] delete[] buff; // Return the concatenated string return temp;}// Overloading the stream// extraction operatoristream& operator>>(istream& is, Mystring& obj){ char* buff = new char[1000]; memset(&buff[0], 0, sizeof(buff)); is >> buff; obj = Mystring{ buff }; delete[] buff; return is;}// Overloading the stream// insertion operatorostream& operator<<(ostream& os, const Mystring& obj){ os << obj.str; return os;}// Function for swapping stringvoid Mystring::swp(Mystring& rhs){ Mystring temp{ rhs }; rhs = *this; *this = temp;}// Function to copy the stringvoid Mystring::copy(char s[], int len, int pos){ for (int i = 0; i < len; i++) { s[i] = str[pos + i]; } s[len] = '\0';}// Function to implement push_bkvoid Mystring::push_bk(char a){ // Find length of string int length = strlen(str); char* buff = new char[length + 2]; // Copy character from str // to buff[] for (int i = 0; i < length; i++) { buff[i] = str[i]; } buff[length] = a; buff[length + 1] = '\0'; // Assign the new string with // char a to string str *this = Mystring{ buff }; // Delete the temp buff[] delete[] buff;}// Function to implement pop_bkvoid Mystring::pop_bk(){ int length = strlen(str); char* buff = new char[length]; // Copy character from str // to buff[] for (int i = 0; i < length - 1; i++) buff[i] = str[i]; buff[length-1] = '\0'; // Assign the new string with // char a to string str *this = Mystring{ buff }; // delete the buff[] delete[] buff;}// Function to implement get_lengthint Mystring::get_length(){ return strlen(str);}// Function to illustrate Constructor// with no argumentsMystring::Mystring() : str{ nullptr }{ str = new char[1]; str[0] = '\0';}// Function to illustrate Constructor// with one argumentsMystring::Mystring(char* val){ if (val == nullptr) { str = new char[1]; str[0] = '\0'; } else { str = new char[strlen(val) + 1]; // Copy character of val[] // using strcpy strcpy(str, val); str[strlen(val)] = '\0'; }}// Function to illustrate// Copy ConstructorMystring::Mystring(const Mystring& source){ str = new char[strlen(source.str) + 1]; strcpy(str, source.str);}// Function to illustrate// Move ConstructorMystring::Mystring(Mystring&& source){ str = source.str; source.str = nullptr;}// Driver Codeint main(){ // Constructor with no arguments Mystring a; // Convert string literal to // char array char temp[] = "Hello"; // Constructor with one argument Mystring b{ temp }; // Copy constructor Mystring c{ a }; char temp1[] = "World"; // One arg constructor called, // then the move constructor Mystring d{ Mystring{ temp } }; // Remove last character from // Mystring b b.pop_bk(); // Print string b cout << "Mystring b: " << b << endl; // Append last character from // Mystring b b.push_bk('o'); // Print string b cout << "Mystring b: " << b << endl; // Print length of string b cout << "Length of Mystring b: " << b << endl; char arr[80]; // Copy string b chars from // length 0 to 3 b.cpy(arr, 3, 0); // Print string arr cout << "arr is: " << arr << endl; // Swap d and b d.swp(b); // Print d and b cout << d << " " << b << endl; // Concatenate b and b with // overloading '+' operator d = b + b; // Print string d cout << "string d: " << d << endl; return 0;}Output:
Mystring b: Hell Mystring b: Hello Length of Mystring b: Hello arr is: Hel Hello Hello string d: HelloHello
