Make Use of UTF-8 Explicit

Php manual describes it as good practice to do so.

Author: oleibman

src/PhpSpreadsheet/Calculation/Engineering/ConvertHex.php

@@ -96,7 +96,7 @@ public static function toDecimal($value)
         }
 
         $binX = '';
-        foreach (mb_str_split($value) as $char) {
+        foreach (mb_str_split($value, 1, 'UTF-8') as $char) {
             $binX .= str_pad(base_convert($char, 16, 2), 4, '0', STR_PAD_LEFT);
         }
         if (strlen($binX) == 40 && $binX[0] == '1') {

src/PhpSpreadsheet/Calculation/Engineering/ConvertOctal.php

@@ -96,7 +96,7 @@ public static function toDecimal($value)
         }
 
         $binX = '';
-        foreach (mb_str_split($value) as $char) {
+        foreach (mb_str_split($value, 1, 'UTF-8') as $char) {
             $binX .= str_pad(decbin((int) $char), 3, '0', STR_PAD_LEFT);
         }
         if (strlen($binX) == 30 && $binX[0] == '1') {

src/PhpSpreadsheet/Calculation/MathTrig/Arabic.php

@@ -81,7 +81,7 @@ public static function evaluate(mixed $roman): array|int|string
         }
 
         try {
-            $arabic = self::calculateArabic(mb_str_split($roman));
+            $arabic = self::calculateArabic(mb_str_split($roman, 1, 'UTF-8'));
         } catch (Exception) {
             return ExcelError::VALUE(); // Invalid character detected
         }

src/PhpSpreadsheet/Reader/Csv/Delimiter.php

@@ -55,7 +55,7 @@ protected function countPotentialDelimiters(): void
 
     protected function countDelimiterValues(string $line, array $delimiterKeys): void
     {
-        $splitString = mb_str_split($line, 1);
+        $splitString = mb_str_split($line, 1, 'UTF-8');
         $distribution = array_count_values($splitString);
         $countLine = array_intersect_key($distribution, $delimiterKeys);
 

src/PhpSpreadsheet/Reader/Security/XmlScanner.php

@@ -87,7 +87,7 @@ private function findCharSet(string $xml): string
     public function scan($xml): string
     {
         // Don't rely purely on libxml_disable_entity_loader()
-        $pattern = '/\0*' . implode('\0*', mb_str_split($this->pattern)) . '\0*/';
+        $pattern = '/\0*' . implode('\0*', mb_str_split($this->pattern, 1, 'UTF-8')) . '\0*/';
 
         $xml = "$xml";
         if (preg_match($pattern, $xml)) {

src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalFormattingRuleExtension.php

@@ -34,7 +34,7 @@ public function __construct(?string $id = null, string $cfRule = self::CONDITION
 
     private function generateUuid(): string
     {
-        $chars = mb_str_split('xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx');
+        $chars = mb_str_split('xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx', 1, 'UTF-8');
 
         foreach ($chars as $i => $char) {
             if ($char === 'x') {

src/PhpSpreadsheet/Style/NumberFormat/DateFormatter.php

@@ -207,6 +207,6 @@ private static function setLowercaseCallback(array $matches): string
 
     private static function escapeQuotesCallback(array $matches): string
     {
-        return '\\' . implode('\\', mb_str_split($matches[1]));
+        return '\\' . implode('\\', mb_str_split($matches[1], 1, 'UTF-8'));
     }
 }