Lära Challenge: Searching Within Strings

Method find()

Sometimes, you may need to search for specific text within a string. This can be done using the .find() or .rfind() methods. Let’s begin with the .find() method.

find.h


              1
            
str.find("text to find")

It returns the index of the first character of the first match.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code") << std::endl; // (code)codefinity
}

You can also specify the position of the first character in the string to be considered in the search. It can be done using the pos argument. Any characters before the pos index are ignored in a search.

Here is an example of finding the first "code" starting from a 3-rd character.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code", 3) << std::endl; // __de(code)finity
}

Method rfind()

You can also locate the last occurrence of some text using the .rfind() method.

rfind.h


              1
            
str.rfind("text to find")

While .find() retrieves the first occurrence of text, .rfind() finds the last occurrence and stands for reverse find.

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code") << std::endl;
    std::cout << str.rfind("code") << std::endl;
}

Note

When .find() or .rfind() cannot locate the substring, they return string::npos. This is a numeric constant that represents an invalid position. It is stored as the largest possible size_t value, which makes it easy to detect failed searches.

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.rfind("abc") << std::endl;
    std::cout << std::string::npos << std::endl;
}

Uppgift

Swipe to start coding

You are building a simple email filter. Your goal is to allow users to register with any email and mark emails from codefinity.com as allowed.

The function isAllowedEmail takes an email as string.

Use rfind() to find the last '@' symbol in the email.
Compare the result of rfind with -1 to check if the '@' symbol exists. If no '@' is found, return false because the email is invalid.
Initialize a string variable domain as an empty string.
Use a for loop starting from atPos + 1 up to the length of email to iterate over characters after the '@'.
In each iteration, append the character to the domain variable.
If domain equals "codefinity.com", return true. Otherwise, return false.

Lösning

Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 3. Kapitel 6

single

Fråga AI

Fråga vad du vill eller prova någon av de föreslagna frågorna för att starta vårt samtal

Suggested prompts:

What is the difference between .find() and .rfind()?

Can you show an example of using the pos argument with .find()?

How does .find() behave if the substring is not found?

Svep för att visa menyn

Method find()

Sometimes, you may need to search for specific text within a string. This can be done using the .find() or .rfind() methods. Let’s begin with the .find() method.

find.h


              1
            
str.find("text to find")

It returns the index of the first character of the first match.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code") << std::endl; // (code)codefinity
}

Here is an example of finding the first "code" starting from a 3-rd character.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code", 3) << std::endl; // __de(code)finity
}

Method rfind()

You can also locate the last occurrence of some text using the .rfind() method.

rfind.h


              1
            
str.rfind("text to find")

While .find() retrieves the first occurrence of text, .rfind() finds the last occurrence and stands for reverse find.

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code") << std::endl;
    std::cout << str.rfind("code") << std::endl;
}

Note

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.rfind("abc") << std::endl;
    std::cout << std::string::npos << std::endl;
}

Uppgift

Swipe to start coding

You are building a simple email filter. Your goal is to allow users to register with any email and mark emails from codefinity.com as allowed.

The function isAllowedEmail takes an email as string.

Use rfind() to find the last '@' symbol in the email.
Compare the result of rfind with -1 to check if the '@' symbol exists. If no '@' is found, return false because the email is invalid.
Initialize a string variable domain as an empty string.
Use a for loop starting from atPos + 1 up to the length of email to iterate over characters after the '@'.
In each iteration, append the character to the domain variable.
If domain equals "codefinity.com", return true. Otherwise, return false.

Lösning

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Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 3. Kapitel 6

single