使用PHP的wordwrap()函数。你可以使用字符串的长度除以2作为第二个参数。下面是一个例子：

<?php
$sentence = 'This is a long sentence that I would like to break up into smaller pieces.';
$width = strlen($sentence)/2;
$wrapped = wordwrap($sentence, $width);
echo $wrapped;
?>

它输出：

This is a long sentence that I would
like to break up into smaller pieces.

如果你想要HTML输出，你可以使用可选的第三个参数来指定分隔符，如下所示：

$wrapped = wordwrap($sentence, $width, '<br />');

• • 已更新**

<?php
$Sentence = 'I will go to the school tomorrow if it is not raining outside and if David is ok with it.';
$Split = explode(' ', $Sentence);

$SplitAt = 0;
foreach($Split as $Word){
    $SplitAt+= strlen($Word)-1;
    if($SplitAt >= strlen($Sentence)){
        break;
    }
}

$NewSentence = wordwrap($Sentence, $SplitAt, '<br />' . PHP_EOL);

echo $NewSentence;
?>

生成以下内容：
如果不是我明天就去学校\n
外面在下雨大卫是否能接受。

• • EDIT**：添加了PHP_EOL以匹配所有系统和html

解如果要选择的行数。

function splitSentence($sentence, $lines) {

    $words                  = explode(' ', $sentence);
    $max_line_length        = intval((strlen($sentence) / $lines));
    $current_line_length    = 0;
    $output                 = '';

    foreach ($words as $word) {
    
        $word_length = strlen($word) + 1; // 1 for removed whitespace

        if (($current_line_length + $word_length) <= $max_line_length) {
            $output .= $word.' ';
            $current_line_length += $word_length;
        }
        else {
            $output .= $word.'<br>';
            $current_line_length = 0;
        }
    }

    return $output;
}