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PHP

PHP Check if String Starts With: Easy Guide

By Filip on 10/27/2024

Learn different methods to efficiently determine if a string starts with a specific string in PHP, using inbuilt functions and regular expressions.

PHP Check if String Starts With: Easy Guide

Table of Contents

Introduction

In PHP, determining if a string begins with a specific substring can be achieved using different methods depending on your PHP version.

Step-by-Step Guide

To check if a string starts with a specific substring in PHP, you can use the str_starts_with() function (available in PHP 8.0 and later):

$string = "Hello world!";
if (str_starts_with($string, "Hello")) {
    echo "The string starts with 'Hello'";
}

For PHP versions prior to 8.0, you can use strncmp():

$string = "Hello world!";
$prefix = "Hello";
if (strncmp($string, $prefix, strlen($prefix)) == 0) {
    echo "The string starts with 'Hello'";
}

This compares the first strlen($prefix) characters of $string with $prefix. If they match, strncmp() returns 0.

Code Example

The code provides two PHP examples to determine if a string begins with a specific substring. The first example utilizes the str_starts_with() function available in PHP 8.0 and later. The second example employs the strncmp() function, suitable for PHP versions prior to 8.0. Both examples demonstrate the process of comparing the string with the desired prefix and outputting a message indicating whether the string starts with the prefix or not.

1. Using str_starts_with() (PHP 8.0 and later):

<?php
$string = "Hello world!";
$prefix = "Hello";

if (str_starts_with($string, $prefix)) {
  echo "The string '$string' starts with '$prefix'";
} else {
  echo "The string '$string' does not start with '$prefix'";
}
?>

Output:

The string 'Hello world!' starts with 'Hello'

2. Using strncmp() (For PHP versions prior to 8.0):

<?php
$string = "Hello world!";
$prefix = "Hello";

if (strncmp($string, $prefix, strlen($prefix)) == 0) {
  echo "The string '$string' starts with '$prefix'";
} else {
  echo "The string '$string' does not start with '$prefix'";
}
?>

Output:

The string 'Hello world!' starts with 'Hello'

Explanation:

  • str_starts_with(): This function takes two arguments: the string to check and the prefix. It returns true if the string starts with the prefix, and false otherwise.
  • strncmp(): This function takes three arguments: the two strings to compare and the length of the prefix. It returns 0 if the first n characters of both strings are equal, where n is the length of the prefix.

Both code examples achieve the same result: checking if a given string starts with a specific substring. Choose the method that best suits your PHP version and coding style.

Additional Notes

  • Case Sensitivity: Both str_starts_with() and strncmp() are case-sensitive. If you need a case-insensitive check, you can convert both the string and the prefix to lowercase using strtolower() before the comparison.
  • Empty Prefix: When the prefix is an empty string, both functions will return true since every string technically starts with an empty string.
  • Performance: For simple checks, both functions are generally fast enough. However, if you are performing many checks or working with very long strings, strncmp() might be slightly faster as it only compares the necessary number of characters.
  • Alternatives:
    • You can also use regular expressions with preg_match() for more complex pattern matching, including checking if a string starts with a specific substring.
    • The strpos() function can also be used, but it requires checking if the returned position is 0, which can be less readable than the dedicated functions.
  • Error Handling: It's good practice to check if the input string is indeed a string using is_string() before using these functions to avoid unexpected errors.

Example with Case-Insensitive Check:

$string = "Hello world!";
$prefix = "hello";

if (str_starts_with(strtolower($string), strtolower($prefix))) {
  echo "The string '$string' starts with '$prefix' (case-insensitive)";
} else {
  echo "The string '$string' does not start with '$prefix' (case-insensitive)";
}
?>

Summary

PHP Version Function Description
8.0+ str_starts_with() Checks if a string starts with a specific substring. Returns true if the string starts with the substring, false otherwise.
< 8.0 strncmp() Compares a specific number of characters from the start of two strings. Returns 0 if the characters match. Requires calculating the length of the prefix using strlen() and comparing it to the function's output.

Conclusion

In conclusion, PHP offers multiple approaches to determine if a string starts with a specific substring. For PHP 8.0 and later, the str_starts_with() function provides a straightforward solution. For earlier versions, strncmp() can be used effectively. When choosing a method, consider factors like code readability, PHP version compatibility, and performance for your specific use case. Remember to handle case sensitivity if required and consider error handling for robust code.

References

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