How Can I Safely Truncate Multibyte Strings in PHP While Preserving Word Boundaries?

Truncating Multibyte Strings in PHP

In PHP, truncating multibyte strings can be a complex task. This article addresses the challenge of truncating such strings to a specified number of characters, considering both multibyte character encoding and word boundaries.

To achieve this, one approach involves using PHP's built-in mb_strimwidth() function, which allows for the truncation of strings with specified widths. However, this function does not take into account word boundaries.

Custom Implementation for Truncation

A custom implementation can be created to handle both multibyte character encoding and word boundaries:

1. Calculate Truncation Length: Subtract the length of the terminator string from the maximum number of characters to truncate.
2. Validate String Length: Check if the input string is longer than the calculated truncation length; otherwise, return it unaltered.
3. Find Word Boundary: Use mb_strrpos() to search for the last space character in the string below the truncation length.
4. Cut String: If a word boundary is found, truncate the string at that point; otherwise, truncate at the calculated truncation length.
5. Append Terminator: Add the terminator string to the truncated string.
6. Return Truncated String: Output the truncated and appended string.

Example Usage:

function truncate($string, $chars = 50, $terminator = ' …') {
  // Calculate truncation length
  $trunc_len = $chars - strlen($terminator);

  // Validate string length
  if (strlen($string) <= $trunc_len) {
    return $string;
  }

  // Find word boundary
  $space_pos = mb_strrpos($string, ' ', -$trunc_len);

  // Cut string
  if ($space_pos !== false) {
    $truncated_string = mb_substr($string, 0, $space_pos);
  } else {
    $truncated_string = mb_strimwidth($string, 0, $trunc_len);
  }

  // Append terminator
  return $truncated_string . $terminator;
}

This function can be used to truncate multibyte strings, considering both character encoding and word boundaries. It provides a straightforward and robust solution for this common PHP task.

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