How to Use the substr() Function in PHP to Extract Substrings

Using the substr() Function in PHP to Extract a Substring

String manipulation is a common task in PHP programming, and extracting a part of a string is a frequent requirement. PHP provides the built-in substr() function to accomplish this. In this article, we will explore the usage of the substr() function with detailed code examples to help you understand and apply this feature effectively.

Basic Usage of the substr() Function

The basic syntax of the substr() function is as follows:

<span class="fun">string substr(string $string, int $start[, int $length])</span>

This function takes three parameters: $string is the original string, $start is the starting position of the substring, and $length is the optional length of the substring. If $length is omitted, the function will extract from the $start position to the end of the string.

Code Example: Extracting a Part of a String

Let's start with a simple example to demonstrate how to use the substr() function to extract a part of a string:

<span class="fun">$str = "Hello, PHP!";</span>

<span class="fun">$substring = substr($str, 7);</span>

<span class="fun">echo $substring; // Output: PHP!</span>

In this example, we extract the substring starting from the 7th character of $str, which results in “PHP!”.

Code Example: Extracting a Substring of a Specific Length

We can also use the substr() function to extract a substring of a specific length:

<span class="fun">$str = "Hello, PHP!";</span>

<span class="fun">$substring = substr($str, 7, 3);</span>

<span class="fun">echo $substring; // Output: PHP</span>

In this example, we start extracting from the 7th character and get the next 3 characters, resulting in “PHP”.

Code Example: Extracting the Last Few Characters of a String

By using a negative value for the $start parameter, we can extract the last few characters of a string:

<span class="fun">$str = "Hello, PHP!";</span>

<span class="fun">$substring = substr($str, -4);</span>

<span class="fun">echo $substring; // Output: PHP!</span>

In this case, we set $start to -4, which means we start from the 4th character from the end of the string, extracting the final portion, which results in “PHP!”.

Code Example: Using substr() to Extract Chinese Characters

For strings containing Chinese characters, the substr() function may not work correctly because Chinese characters consist of multiple bytes. In such cases, we should use the mb_substr() function, which supports multi-byte characters.

<span class="fun">$str = "你好，PHP！";</span>

<span class="fun">$substring = mb_substr($str, 3, 3, 'UTF-8');</span>

<span class="fun">echo $substring; // Output: PHP</span>

Here, we use mb_substr() to extract 3 characters starting from position 3 in the string $str, and the result is “PHP”.

Important Notes When Using substr()

• The $start parameter specifies the starting position. If it is negative, the position is counted from the end of the string.
• The $length parameter specifies the length of the substring. If omitted, the function extracts from $start to the end of the string.
• For strings with multi-byte characters, it is recommended to use the mb_substr() function and specify the character encoding as UTF-8.

With these examples, you should have a solid understanding of how to use the substr() function in PHP. We hope these examples help you in performing string manipulation tasks effectively.