A 'pit' in PHP, PHP 'pit'_PHP Tutorial

A "pit" in PHP, a "pit" in PHP

Let's talk about a problem that is very likely to be encountered at work - a reference to foreach

<span>$arr</span> = <span>range</span>(1,3<span>);
</span><span>//</span><span>[1,2,3]</span>

<span>foreach</span>(<span>$arr</span> <span>as</span> &<span>$val</span><span>) {
}

</span><span>foreach</span>(<span>$arr</span> <span>as</span> <span>$val</span><span>) {
}
</span><span>print_r</span>(<span>$arr</span><span>);
 </span>

What does the above code output? The amazing thing is as follows. I encountered this once at work. It took me a long time to figure out the reason, but I just found a solution. There are two ways to solve this problem. Number:

<span>Array</span><span>
(
    [</span>0] => 1<span>
    [</span>1] => 2<span>
    [</span>2] => 2<span>
)</span>

The following two methods can solve the above problem:

<span>//</span><span>方法1</span>
<span>foreach</span> (<span>$arr</span> <span>as</span> &<span>$value</span><span>) {
}
</span><span>unset</span>(<span>$value</span><span>);
</span><span>foreach</span> (<span>$arr</span> <span>as</span> <span>$value</span><span>) {
}
</span><span>print_r</span>(<span>$arr</span><span>);
</span><span>//</span><span>[1,2,3]

//方法2</span>
<span>foreach</span> (<span>$arr</span> <span>as</span> &<span>$value</span><span>) {
}
</span><span>foreach</span> (<span>$arr</span> <span>as</span> <span>$val</span><span>) {
}
</span><span>print_r</span>(<span>$arr</span><span>);
</span><span>//</span><span>[1,2,3]
//方法3</span>
<span>foreach</span> (<span>$arr</span> <span>as</span> &<span>$value</span><span>) {
}
</span><span>foreach</span> (<span>$arr</span> <span>as</span> &<span>$value</span><span>) {
}
</span><span>print_r</span>(<span>$arr</span><span>);
</span><span>//</span><span>[1,2,3]</span>

Method 1 can also be seen in the official manual http://php.net/manual/en/control-structures.foreach.php. There is a special tip in the article to remind this $ var = 123; $tmp = &$var; $tmp = 200; echo $var; //200

Take a look at the stolen picture below (haha, the original link is posted below) to have a better understanding of the above

8874306e90966e7de1b8899554838cae 1, "b" => 2, "c" => 3); $arr2 = array("x" => 4, "y" => 5, "z" => 6); foreach ($arr1 as $key => &$val) {} foreach ($arr2 as $key => $val) { } var_dump($arr1); var_dump($arr2); ?> The output is: array(3) { ["a"]=> int(1) ["b"]=> int(2) ["c"]=> &int(6) } array(3) { ["x"]=> int(4) ["y"]=> int(5) ["z"]=> int(6) }

Reference article:

　http://www.cnblogs.com/CraryPrimitiveMan/p/4030748.html#3085766

http://www.jb51.net/article/39299.htm

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