How Can I Precisely Truncate Multibyte Strings While Maintaining Word Boundaries?

Truncating Multibyte Strings with Precision

Introduction

Truncating strings to a specific character length is a common task in programming. However, when dealing with multibyte strings, which may contain characters with varying widths, it becomes more complex. This question delves into the nuances of truncating multibyte strings while preserving word boundaries.

PHP's mb_strimwidth Function

As suggested by the answer, PHP provides a convenient function called mb_strimwidth() that handles truncation of multibyte strings. It takes the string, desired width, and an optional terminator as arguments. However, this function does not take into account word boundaries.

Custom Truncation Algorithm

To achieve word boundary truncation, a custom algorithm can be used:

function truncate($string, $chars = 50, $terminator = ' …') {
    // Calculate the maximum length considering the terminator
    $max_length = $chars - mb_strlen($terminator);

    // Short circuit for strings shorter than the maximum length
    if (mb_strlen($string) <= $max_length) {
        return $string;
    }

    // Find the last space character within the maximum length
    $last_space_index = mb_strrpos($string, ' ', $max_length);

    // Cut the string at the last space or at the maximum length if no last space is found
    $truncated_string = (false !== $last_space_index)
        ? mb_substr($string, 0, $last_space_index)
        : mb_strimwidth($string, 0, $chars);

    // Append the terminator
    $truncated_string .= $terminator;

    return $truncated_string;
}

This function implements the steps described in the question:

1. Calculate the maximum length.
2. Validate if the string is longer than the maximum length.
3. Find the last space character below the maximum length.
4. Cut the string accordingly.
5. Append the terminator.
6. Return the truncated string.

Demonstration

The following code demonstrates the usage of the custom truncation function:

$in = "Answer to the Ultimate Question of Life, the Universe, and Everything.";
$out = truncate($in, 50, ' …');

echo $out; // "Answer to the Ultimate Question of Life, the …"

Conclusion

PHP's mb_strimwidth() function provides a straightforward way to truncate multibyte strings, but it does not consider word boundaries. By implementing a custom algorithm, we can achieve more precise truncation that preserves the integrity of word boundaries.

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