How do I check if a string contains a specific word?

Checking if a string contains a specific word is a common task in programming and can be accomplished using various techniques and functions. In this detailed discussion, we’ll explore different methods in PHP for determining if a string contains a specific word, examining both basic and more advanced approaches.

1. Using ‘strpos()’ Function

The ‘strpos()’ function is a built-in PHP function that searches for the first occurrence of a substring within a string. It returns the position of the first occurrence or ‘false’ if the substring is not found.

Example:

$string = "This is a sample string.";
$wordToFind = "sample";

if (strpos($string, $wordToFind) !== false) {
    echo "The string contains the word '{$wordToFind}'.";
} else {
    echo "The string does not contain the word '{$wordToFind}'.";
}

In this example, ‘strpos()’ is used to check if the word “sample” is present in the given string. Note the use of ‘! == false’ in the condition to correctly evaluate whether the word is found.

2. Case-Insensitive Search

If case sensitivity is not a concern, you can convert both the string and the word to lowercase or uppercase before performing the check.

$string = "This is a sample string.";
$wordToFind = "SAMPLE";

if (strpos(strtolower($string), strtolower($wordToFind)) !== false) {
    echo "The string contains the word '{$wordToFind}' (case-insensitive).";
} else {
    echo "The string does not contain the word '{$wordToFind}'.";
}

By converting both the string and the word to lowercase using ‘strtolower()’, you ensure a case-insensitive comparison.

3. Using ‘strpos()’ for Case-Insensitive Search

The ‘stripos()’ function is similar to ‘strpos()’ but performs a case-insensitive search directly.

$string = "This is a sample string.";
$wordToFind = "SAMPLE";

if (stripos($string, $wordToFind) !== false) {
    echo "The string contains the word '{$wordToFind}' (case-insensitive).";
} else {
    echo "The string does not contain the word '{$wordToFind}'.";
}

This method eliminates the need to convert the string and the word to lowercase explicitly.

4. Regular Expressions (Regex)

Regular expressions provide a powerful and flexible way to search for patterns in strings. The ‘preg_match()’ function can be used for this purpose.

$string = "This is a sample string.";
$wordToFind = "sample";

if (preg_match("/\b{$wordToFind}\b/i", $string)) {
    echo "The string contains the word '{$wordToFind}' (case-insensitive).";
} else {
    echo "The string does not contain the word '{$wordToFind}'.";
}

Here, the ‘\b’ word boundary anchors ensure that the match is a whole word, and the ‘i’ modifier makes the search case-insensitive.

5. Using ‘str_contains()’ (PHP 8 and later)

PHP 8 introduced the ‘str_contains()’ function, providing a simple and concise way to check if a string contains another string.

$string = "This is a sample string.";
$wordToFind = "sample";

if (str_contains($string, $wordToFind)) {
    echo "The string contains the word '{$wordToFind}'.";
} else {
    echo "The string does not contain the word '{$wordToFind}'.";
}

This function returns a boolean value, making it clear and efficient for this type of check.

6. Exploring ‘substr_cont()’

The ‘substr_cont()’ function can be used to count the number of occurrences of a substring within a string. While it doesn’t directly check if a string contains a specific word, it can be adapted for such a check.

$string = "This is a sample string.";
$wordToFind = "sample";

if (substr_count(strtolower($string), strtolower($wordToFind)) > 0) {
    echo "The string contains the word '{$wordToFind}' (case-insensitive).";
} else {
    echo "The string does not contain the word '{$wordToFind}'.";
}

By counting the occurrences, you can determine if the word appears in the string.

7. Performance Considerations

The choice of method depends on factors such as the size of the string, the frequency of the operation, and the desired case sensitivity. Functions like ‘str_contains()’ and ‘stripos()’ are generally more concise and readable, but for large strings or frequent operations, performance considerations might influence your choice.

8. Handling Multibyte Characters

When working with multibyte character encodings like UTF-8, it’s important to use functions that support such encodings. The ‘mb_stripos()’ and ‘mb_stristr()’ functions in the ‘mbstring’ extension can be used for case-insensitive searches with multibyte support.

Example:

$string = "This is a sample string with café.";
$wordToFind = "Café";

if (mb_stripos($string, $wordToFind) !== false) {
    echo "The string contains the word '{$wordToFind}' (case-insensitive, multibyte).";
} else {
    echo "The string does not contain the word '{$wordToFind}'.";
}

Ensure that the ‘mbstring’ extension is enabled in your PHP configuration.

Conclusion

Checking if a string contains a specific word is a fundamental task in PHP programming. The choice of method depends on factors such as case sensitivity, performance requirements, and the PHP version you are using. The examples provided cover a range of techniques, from basic functions like ‘strpos()’ to more advanced options like regular expressions and PHP 8’s ‘str_contains()’. Consider the specific needs of your application and choose the method that best fits your requirements for clarity, efficiency, and flexibility.