String search functions (strpos, strstr) in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the strpos function do in PHP?

It finds the position of the first occurrence of a substring in a string. If the substring is found, it returns the index (starting at 0). If not found, it returns false.

beginner

What is the difference between strpos and strstr?

strpos returns the position (number) of the substring in the string. strstr returns the part of the string starting from the first occurrence of the substring to the end.

beginner

What does strstr return if the substring is not found?

It returns false if the substring is not found in the string.

intermediate

How does strpos handle the case when the substring is at the very start of the string?

It returns 0 because the substring starts at the first character (index 0). Remember, 0 is a valid position, not false.

intermediate

How can you safely check if a substring exists using strpos?

Use the strict comparison operator !== false because strpos can return 0 (which is falsey). For example: if (strpos($text, 'word') !== false) { /* found */ }

What does strpos('hello world', 'world') return?

A 6

B 0

C false

D 11

The substring 'world' starts at index 6 in 'hello world'.

What will strstr('hello world', 'world') return?

A 'world' plus the rest of the string starting from 'world'

B 'hello world'

C 'world' plus the rest of the string

D 'world'

strstr returns the part of the string starting from the first occurrence of the substring to the end, so it returns 'world'.

What does strpos('apple', 'a') return?

A false

B 0

C 1

D 5

The substring 'a' is at the start of 'apple', so the position is 0.

If strpos returns 0, what does that mean?

A Substring found at the end

B Substring not found

C Error in function

D Substring found at the start

0 means the substring is found at the very start of the string.

Which is the correct way to check if 'cat' is in a string $text?

A if (strpos($text, 'cat') == true) { ... }

B if (strpos($text, 'cat')) { ... }

C if (strpos($text, 'cat') !== false) { ... }

D if (strpos($text, 'cat') == false) { ... }

Use strict comparison !== false to correctly detect substring presence, even if at position 0.

Explain how strpos works and how to correctly check if a substring exists in a string.

Think about what happens if the substring is at the start.

Describe the behavior of strstr and what it returns when the substring is found or not found.

It returns a string, not a number.