Replace Substring in C++

Replacing a substring within a std::string with another string is accomplished using the replace() method. This method allows you to specify the starting position, the number of characters to replace, and the new substring.

Basic Usage

The replace() method requires three arguments: the starting position, the number of characters to replace, and the new substring. For example:

1#include <iostream>
2#include <string>
3
4int main(){
5  std::string Greeting{"Hello World!"};
6
7  Greeting.replace(6, 5, "Everyone");
8
9  std::cout << Greeting;
10}

1Hello Everyone!

Replacing with a Different Length

The new substring does not need to be the same length as the substring being replaced. The string will adjust its size accordingly.

1#include <iostream>
2#include <string>
3
4int main(){
5  std::string Greeting{"Hello Everyone!"};
6
7  Greeting.replace(6, 8, "World");
8
9  std::cout << Greeting;
10}

1Hello World!

Using Iterators

You can also use iterators to specify the range of characters to replace. This can be useful when working with more complex string manipulations.

1#include <iostream>
2#include <string>
3
4int main() {
5  std::string Greeting{"Hello World!"};
6  std::string Replacement{"Everyone"};
7
8  Greeting.replace(Greeting.begin() + 6,   
9                   Greeting.begin() + 11,  
10                   Replacement);  
11
12  std::cout << Greeting;
13}

1Hello Everyone!

Considerations

• Bounds Checking: Ensure the starting position and length are within the bounds of the string to avoid undefined behavior.
• Efficiency: Large replacements can be inefficient due to potential reallocations.

Advanced Usage

For more control, you can replace a substring from another string by specifying the starting position and length within the new string.

1#include <iostream>
2#include <string>
3
4int main() {
5  std::string Greeting{"Hello World!"};
6  std::string Replacement{"Greetings Earthlings"};
7
8  Greeting.replace(6, 5, Replacement, 10, 5);  
9
10  std::cout << Greeting;
11}

1Hello Earth!

The replace() method is powerful and flexible, making it easy to modify parts of a std::string as needed.