String search functions (strpos, strstr) in PHP - Step-by-Step Execution

Concept Flow - String search functions (strpos, strstr)

Start with string and search term

↓

Call strpos or strstr

↓

Check if search term found?

No→Return false

Yes↓

Return position (strpos) or substring (strstr)

↓

Use result

The program starts with a string and a search term, calls strpos or strstr, checks if the term is found, then returns the position or substring accordingly.

Execution Sample

PHP

<?php
$text = "hello world";
$pos = strpos($text, "world");
$sub = strstr($text, "world");
echo $pos . " " . $sub;
?>

This code searches for "world" in "hello world" using strpos and strstr, then prints the position and substring.

Execution Table

Step	Function Call	Input String	Search Term	Result	Explanation
1	strpos($text, "world")	"hello world"	"world"	6	"world" starts at index 6 in "hello world"
2	strstr($text, "world")	"hello world"	"world"	"world"	Returns substring from "world" to end
3	echo $pos . " " . $sub	N/A	N/A	6 world	Prints position and substring

💡 All steps complete; strpos found "world" at index 6; strstr returned substring "world"

Variable Tracker

Variable	Start	After strpos	After strstr	Final
$text	"hello world"	"hello world"	"hello world"	"hello world"
$pos	undefined	6	6	6
$sub	undefined	undefined	"world"	"world"

Key Moments - 3 Insights

Why does strpos return 6 instead of 7 for the position?

Because strpos counts from zero, so the first character 'h' is index 0, making 'w' in 'world' at index 6 (see execution_table step 1).

What happens if the search term is not found?

strpos returns false and strstr returns false, so you should check the result before using it (not shown in this example).

Why does strstr return only 'world' and not the whole string?

strstr returns the part of the string starting from the search term to the end (see execution_table step 2).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of $pos after step 1?

A 6

B 5

C false

D 7

💡 Hint

Check the 'Result' column in execution_table row for step 1.

At which step does strstr return the substring starting from the search term?

A Step 1

B Step 3

C Step 2

D No step returns substring

💡 Hint

Look at the 'Function Call' and 'Result' columns in execution_table.

If the search term was not found, what would strpos return?

A 0

B false

C empty string

D -1

💡 Hint

Recall that strpos returns false when the term is missing (see key_moments).

Concept Snapshot

strpos(string, search) returns the position of search in string (0-based index).
strstr(string, search) returns substring from search to end.
If search not found, strpos returns false.
Use === to check strpos result to avoid confusion with 0.
strstr returns false if not found.
Useful for finding or extracting parts of strings.

Full Transcript

This example shows how PHP string search functions strpos and strstr work. We start with a string 'hello world' and search for 'world'. strpos returns 6 because 'world' starts at index 6 (counting from zero). strstr returns the substring 'world' from that position to the end. If the search term is not found, strpos returns false, so you should check the result carefully. strstr also returns false if not found. These functions help find positions or parts of strings easily.