What are the functions of the php strstr function?

The main functionalities of the PHP strstr function are as follows:

1. Search for a substring in a string: The strstr function can search for a specified substring within a string and return the position of the first occurrence of the substring along with the rest of the substring. If the substring is not found, it returns false.
2. To determine if a string contains a specified substring: you can ascertain whether the return value of the strstr function is false.
3. Find the substring in a string and return its preceding part: You can control the return value of the strstr function by specifying a third parameter. If set to true, it will return the part of the string before the substring; if set to false (default), it will return the part of the string after the substring.
4. To determine if a string starts with a specific substring: set the third parameter to true. If the returned string is equal to the specified substring, it means the original string starts with the specified substring.
5. To check if a string ends with a specified substring, you can achieve this by setting the third parameter to true. If the returned string is equal to the specified substring, it means that the original string ends with the specified substring.

In summary, the strstr function is mainly used to search for and evaluate substrings within a string, and then return the corresponding result.