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PHP recursively creates multi-level directories (the process of solving an interview question), PHP recursively

I saw an interview question today and asked me to write a method that can create multi-level directories. Function:


My first impression is to use recursion to create, the specific idea is as follows:

<span>function</span> Directory(<span>$dir</span><span>){

</span><span>    if</span>(<span>is_dir</span>(<span>$dir</span>) || @<span>mkdir</span>(<span>$dir</span>,0777)){ <span>//</span><span>查看目录是否已经存在或尝试创建,加一个@抑制符号是因为第一次创建失败,会报一个&ldquo;父目录不存在&rdquo;的警告。</span>

        <span>echo</span> <span>$dir</span>."创建成功<br>";   <span>//</span><span>输出创建成功的目录</span>
<span>
    }</span><span>else</span><span>{

        </span><span>$dirArr</span>=<span>explode</span>('/',<span>$dir</span>); <span>//</span><span>当子目录没创建成功时,试图创建父目录,用explode()函数以'/'分隔符切割成一个数组</span>

        <span>array_pop</span>(<span>$dirArr</span>); <span>//</span><span>将数组中的最后一项(即子目录)弹出来,</span>

        <span>$newDir</span>=<span>implode</span>('/',<span>$dirArr</span>); <span>//</span><span>重新组合成一个文件夹字符串</span>
<span>
        Directory(</span><span>$newDir</span>); <span>//</span><span>试图创建父目录</span>

        <span>if</span>(@<span>mkdir</span>(<span>$dir</span>,0777<span>)){

            </span><span>echo</span> <span>$dir</span>."创建成功<br>"<span>;

        } </span><span>//</span><span>再次试图创建子目录,成功输出目录名</span>
<span>
    }

}

Directory(</span>"A/B/C/D/E/F");

The output result is as shown below:


But it can be seen that it is too troublesome to write. Looking at the file functions in the manual, I saw a dirname() function, whose prototype is as follows:

<p>string dirname ( string $path )</p>
<p>给出一个包含有指向一个文件的全路径的字符串,本函数返回去掉文件名后的目录名。 </p>
<p>在 Windows 中,斜线(/)和反斜线(\)都可以用作目录分隔符。在其它环境下是斜线(/)。</p>

Can be slightly optimized:

<span>function</span> Directory(<span>$dir</span><span>){

    </span><span>if</span>(<span>is_dir</span>(<span>$dir</span>) || @<span>mkdir</span>(<span>$dir</span>,0777<span>)){ 

        </span><span>echo</span> <span>$dir</span>."创建成功<br>"<span>;   

    }</span><span>else</span><span>{

        Directory(</span><span>dirname</span>(<span>$dir</span><span>));

        </span><span>if</span>(@<span>mkdir</span>(<span>$dir</span>,0777<span>)){

            </span><span>echo</span> <span>$dir</span>."创建成功<br>"<span>;

        }

    }

}</span>

The effect is the same.


Afterwards, I searched for answers on the Internet and found an extremely insightful one:

<span>function</span>  Directory( <span>$dir</span><span> ){    

     </span><span>return</span>   <span>is_dir</span> ( <span>$dir</span> )  or  Directory(<span>dirname</span>( <span>$dir</span> ))  and   <span>mkdir</span> ( <span>$dir</span> , 0777<span>);

}</span>

Now let’s explain the whole function:

First introduce the priority order of logical operators in PHP: && > || > and > or , that is, symbolic type > letter type, AND type >OR type, so the function body can be seen as:

is_dir ( $dir ) or (Directory(dirname( $dir )) and mkdir ( $dir , 0777));

First determine whether the target directory exists. If it exists, depending on the short-circuit characteristics of or, the entire following will be short-circuited and execution will be skipped; if the target directory does not exist, the following function body will be executed:

Directory(dirname( $dir )) and mkdir ( $dir , 0777)

I considered the purpose of performing recursion first: performing recursion first is to confirm that its parent directory (dirname($dir)) has been created so that the subsequent mkdir() function will not be unable to find the subdirectory when it is created. to the parent directory to issue a warning.

After entering the depth of the recursion, confirm that the deepest root directory exists, and then create directories from the root directory downwards.


Finally, I suggest those who are looking for a job to go online and find some interview questions from large companies to do. After all, their exams are more comprehensive and in-depth. When learning knowledge, you should also brush up on the questions, and you must also do it. , because it’s easy to have too much ambition but too little. I optimized the function at the beginning several times before it could be used normally.

I will also find some interesting interview questions to share with you in the future.

If you think this blog post is helpful to you, you can recommend or follow me. If you have any questions, you can leave a message below for discussion. Thank you.

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