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

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:

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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:

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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.

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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.

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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.

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