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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

find.h

copy

              
1

            
str.find("text to find")

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

main.cpp

main.cpp

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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

main.cpp

copy

              
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

rfind.h

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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

main.cpp

copy

              
12345678

            
#include <iostream>

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

Note

If no match is found, both .find() and .rfind() return a special value, string::npos. This value represents no position and indicates that the search was unsuccessful.

main.cpp

main.cpp

copy

              
12345678

            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.rfind("abc") << std::endl;
    std::cout << std::string::npos << std::endl;
}
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Create a program that prints "Found code" if the string contains "code", and "No code" if it doesn’t.

  1. Write a condition to check for no match using .find() or .rfind(). Refer to the hint if needed.
  2. Replace the "___" placeholders with "Found code" or "No code", based on your if statement.

Lösning

solution.cpp

solution.cpp

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book
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

find.h

copy

              
1

            
str.find("text to find")

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

main.cpp

main.cpp

copy

              
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

main.cpp

copy

              
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

rfind.h

copy

              
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

main.cpp

copy

              
12345678

            
#include <iostream>

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

Note

If no match is found, both .find() and .rfind() return a special value, string::npos. This value represents no position and indicates that the search was unsuccessful.

main.cpp

main.cpp

copy

              
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

Create a program that prints "Found code" if the string contains "code", and "No code" if it doesn’t.

  1. Write a condition to check for no match using .find() or .rfind(). Refer to the hint if needed.
  2. Replace the "___" placeholders with "Found code" or "No code", based on your if statement.

Lösning

solution.cpp

solution.cpp

Switch to desktopByt till skrivbordet för praktisk övningFortsätt där du är med ett av alternativen nedan
Var allt tydligt?

Hur kan vi förbättra det?

Tack för dina kommentarer!

close

Awesome!

Completion rate improved to 4.35

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