std::string::append vs std::string::push_back() vs Operator += in C++
Last Updated : 08 Nov, 2022
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To append characters, you can use operator +=, append(), and push_back(). All of them helps to append character but with a little difference in implementation and application.
- Operator += : appends single-argument values. Time complexity : O(n)
- append() : lets you specify the appended value by using multiple arguments. Time complexity: O(n)
- push_back() : lets you to append single character at a time. Time complexity: O(1)
Here are few standards we can have for comparison among these three:
1) Full String:
- += : We can append full string using +=.
- append() : We can also append full string using append().
- push_back : doesn't allow appending of full string.
Implementation:
// CPP code for comparison on the
// basis of appending Full String
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate comparison among
// +=, append(), push_back()
void appendDemo(string str1, string str2)
{
string str = str1;
// Appending using +=
str1 += str2;
cout << "Using += : ";
cout << str1 << endl;
// Appending using append()
str.append(str2);
cout << "Using append() : ";
cout << str << endl;
}
// Driver code
int main()
{
string str1("Hello World! ");
string str2("GeeksforGeeks");
cout << "Original String : " << str1 << endl;
appendDemo(str1, str2);
return 0;
}
Output
Original String : Hello World! Using += : Hello World! GeeksforGeeks Using append() : Hello World! GeeksforGeeks
2) Appending part of String:
- += : Doesn't allow appending part of string.
- append() : Allows appending part of string.
- push_back : We can't append part of string using push_back.
Implementation:
// CPP code for comparison on the basis of
// Appending part of string
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate comparison among
// +=, append(), push_back()
void appendDemo(string str1, string str2)
{
// Appends 5 characters from 0th index of
// str2 to str1
str1.append(str2, 0, 5);
cout << "Using append() : ";
cout << str1;
}
// Driver code
int main()
{
string str1("GeeksforGeeks ");
string str2("Hello World! ");
cout << "Original String : " << str1 << endl;
appendDemo(str1, str2);
return 0;
}
Output
Original String : GeeksforGeeks Using append() : GeeksforGeeks Hello
3) Appending C-string (char*):
- += : Allows appending C-string
- append() : It also allows appending C-string
- push_back : We cannot append C-string using push_back().
Implementation:
// CPP code for comparison on the basis of
// Appending C-string
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate comparison among
// +=, append(), push_back()
void appendDemo(string str)
{
string str1 = str;
// Appending using +=
str += "GeeksforGeeks";
cout << "Using += : ";
cout << str << endl;
// Appending using append()
str1.append("GeeksforGeeks");
cout << "Using append() : ";
cout << str1 << endl;
}
// Driver code
int main()
{
string str("World of ");
cout << "Original String : " << str << endl;
appendDemo(str);
return 0;
}
Output
Original String : World of Using += : World of GeeksforGeeks Using append() : World of GeeksforGeeks
4) Appending character array:
- += : Allows appending of character array
- append() : Allows appending of character array.
- push_back : Does not allow char array appending.
Implementation:
// CPP code for comparison on the basis of
// Appending character array
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate comparison among
// +=, append(), push_back()
void appendDemo(string str)
{
char ch[6] = { 'G', 'e', 'e', 'k', 's', '\0' };
string str1 = str;
// Appending using +=
str += ch;
cout << "Using += : " << str << endl;
// Appending using append()
str1.append(ch);
cout << "Using append() : ";
cout << str1 << endl;
}
// Driver code
int main()
{
string str("World of ");
cout << "Original String : " << str << endl;
appendDemo(str);
return 0;
}
Output
Original String : World of Using += : World of Geeks Using append() : World of Geeks
5) Appending single character:
- += : We can append single character using += operator.
- append() : Allows appending single character.
- push_back : Allows appending single character.
// CPP code for comparison on the basis of
// Appending single character
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate comparison among
// +=, append(), push_back()
void appendDemo(string str)
{
string str1 = str;
string str2 = str;
// Appending using +=
str += 'C';
cout << "Using += : " << str << endl;
// Appending using append()
str2.append("C");
cout << "Using append() : ";
cout << str2 << endl;
// Appending using push_back()
str1.push_back('C');
cout << "Using push_back : ";
cout << str1;
}
// Driver code
int main()
{
string str("AB");
cout << "Original String : " << str << endl;
appendDemo(str);
return 0;
}
Output
Original String : AB Using += : ABC Using append() : ABC Using push_back : ABC
6) Iterator range:
- += : Doesn't provide iterator range.
- append() : Provides iterator range.
- push_back : Doesn't provide iterator range.
Implementation:
// CPP code for comparison on the basis of
// Appending using iterator range
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate comparison among
// +=, append(), push_back()
void appendDemo(string str1, string str2)
{
// Appends all characters from
// str2.begin()+5, str2.end() to str1
str1.append(str2.begin() + 5, str2.end());
cout << "Using append : ";
cout << str1;
}
// Driver code
int main()
{
string str1("Hello World! ");
string str2("GeeksforGeeks");
cout << "Original String : " << str1 << endl;
appendDemo(str1, str2);
return 0;
}
Output
Original String : Hello World! Using append : Hello World! forGeeks
7) Return Value:
- += : Return *this.
- append() : Returns *this
- push_back : Doesn't return anything.
Implementation:
// CPP code for comparison on the basis of
// Return value
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate comparison among
// +=, append(), push_back()
string appendDemo(string str1, string str2)
{
// Appends str2 in str1
str1.append(str2); // Similarly with str1 += str2
cout << "Using append : ";
// Returns *this
return str1;
}
// Driver code
int main()
{
string str1("Hello World! ");
string str2("GeeksforGeeks");
string str;
cout << "Original String : " << str1 << endl;
str = appendDemo(str1, str2);
cout << str;
return 0;
}
Output
Original String : Hello World! Using append : Hello World! GeeksforGeeks
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