PHP中的一个”坑“,PHP"坑"
PHP中的一个”坑“,PHP"坑"
说一个极有可能在工作中遇到的问题——foreach的引用
<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>
上面这段代码输出什么呢,神奇的竟然是下面这样,这个我在工作中遇到过一次,当时弄了半天没弄出个所以然,只是找到了解决办法,这个问题解决办法有两个:
<span>Array</span><span> ( [</span>0] => 1<span> [</span>1] => 2<span> [</span>2] => 2<span> )</span>
下面这两种方式都可以解决上面这个问题:
<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>
方法1在官方的手册中也可以看到http://php.net/manual/en/control-structures.foreach.php,文章中专门有个tips提示这一点$var = 123; $tmp = &$var; $tmp = 200; echo $var; //200
看看下面这张盗来的图(哈哈,原文链接贴在下面),对上面这个更好的理解
php $arr1 = array("a" => 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) }
参考文章:
http://www.cnblogs.com/CraryPrimitiveMan/p/4030748.html#3085766
http://www.jb51.net/article/39299.htm
本文版权归作者iforever(luluyrt@163.com)所有,未经作者本人同意禁止任何形式的转载,转载文章之后必须在文章页面明显位置给出作者和原文连接,否则保留追究法律责任的权利。

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