How Can I Check If a C String Contains a Substring?

Finding a Substring in a C String

Given a string stored in a std::string variable, it is often necessary to determine if it contains a specific substring. C provides a straightforward method to perform this check using the std::string::find function.

The syntax of std::string::find is as follows:

std::string::size_type find(const std::string& str, int pos = 0) const;

where:

• str is the substring to search for.
• pos is an optional starting position to begin the search from (default is 0).

The function returns a std::string::size_type value, which represents the index of the first occurrence of the specified substring. If the substring is not found, it returns std::string::npos.

To check if a string contains a substring, you can use the following code:

if (s1.find(s2) != std::string::npos) {
    std::cout << "found!" << '\n';
}

where:

• s1 is the string to search in.
• s2 is the substring to search for.

If s2 is found in s1, the std::string::npos check will fail, resulting in a "found!" message being printed. Note that the search is case-sensitive, meaning that s2 must exactly match the characters in s1.

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