Seven classic PHP interview questions (with answers)

This article introduces you to seven classic PHP interview questions (with answers). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.

1. There are several ways to merge two arrays. Try to compare their similarities and differences

Ways:

1, array_merge()

2, ' '

3. array_merge_recursive

Similarities and differences:

array_merge simply merges arrays

array_merge_recursive merges two arrays. If there is exactly the same data in the array, merge them recursively

array_combine and ' ': merge two arrays, and the value of the former is used as the key of the new array

2. Please write a function to check whether the data submitted by the user is an integer (regardless of data type, it can be binary, octal, decimal, or hexadecimal numbers)

Answer: In fact, the main ones are is_int and floor This method

if(!is_numeric($jp_total)||strpos($jp_total,".")!==false){  
    echo "不是整数";  
}else{  
    echo "是整数";  
}

3． PHP's strtolower () and strtoupper () functions may cause Chinese characters to be converted into garbled characters on servers with non-Chinese systems installed. Please write two alternative functions to achieve string case conversion compatible with Unicode text

Answer: The reason is: Chinese is composed of multi-bytes, and only a single English character in the English system has only one byte, so the system performs strtolower () processing on every byte of Chinese. After the change The Chinese characters become garbled when spliced ​​together (the characters corresponding to the newly generated encoding map may not be Chinese)

Manual solution: Use str_split (string string, intstring, intsplit_length = 1) to press each Byte cutting, like Chinese can be cut into three bytes. If the recognized bytes are English letters, they will be converted.

<?php  
function mystrtoupper($a){  
    $b = str_split($a, 1);  
    $r = &#39;&#39;;  
    foreach($b as $v){  
        $v = ord($v);  
        if($v >= 97 && $v<= 122){  
            $v -= 32;  
        }  
        $r .= chr($v);  
    }  
    return $r;  
}  
$a = &#39;a中你继续F@#$%^&*(BMDJFDoalsdkfjasl&#39;;  
echo &#39;origin string:&#39;.$a." ";  
echo &#39;result string:&#39;;  
$r = mystrtoupper($a);  
var_dump($r);

4． There is a bug in PHP's is_writeable () function. It cannot accurately determine whether a directory/file is writable. Please write a function to determine whether the directory/file is absolutely writable.

Answer: There are two aspects of the bug. ,

1. In windows, when the file has only read-only attributes, the is_writeable () function returns false. When true is returned, the file is not necessarily writable.

If it is a directory, create a new file in the directory and check by opening the file;

If it is a file, you can test whether the file is writable by opening the file (fopen).

2. In Unix, when safe_mode is turned on in the php configuration file (safe_mode=on), is_writeable () is also unavailable.

Read the configuration file to see if safe_mode is turned on.

/**
* Tests for file writability
*
* is_writable() returns TRUE on Windows servers when you really can't write to
* the file, based on the read-only attribute. is_writable() is also unreliable
* on Unix servers if safe_mode is on.
*
* @access   private
* @return   void
*/
if ( ! function_exists('is_really_writable'))
{
    function is_really_writable($file){
    // If we're on a Unix server with safe_mode off we call is_writable
    if (DIRECTORY_SEPARATOR == '/' AND @ini_get("safe_mode") == FALSE){
        return is_writable($file);
    }
    // For windows servers and safe_mode "on" installations we'll actually
    // write a file then read it. Bah...
    if (is_dir($file)){
        $file = rtrim($file, '/').'/'.md5(mt_rand(1,100).mt_rand(1,100));
        if (($fp = @fopen($file, FOPEN_WRITE_CREATE)) === FALSE){
            return FALSE;
        }
        fclose($fp);
        @chmod($file, DIR_WRITE_MODE);
        @unlink($file);
        return TRUE;
    } elseif ( ! is_file($file) OR ($fp = @fopen($file, FOPEN_WRITE_CREATE)) === FALSE) {
        return FALSE;
    }
    fclose($fp);
    return TRUE;
    }
}

5． There is a bug in PHP's chmod () function, and the setting cannot be guaranteed to be successful. Please write a function to create a directory/file under the specified path and ensure that the permission mask can be set correctly

Answer: I can't find it either To the answer

6． PHP processes the file type in the uploaded file information array $_FILES ['type'] is provided by the client browser. It may be information forged by hackers. Please write a function to ensure that the image file type uploaded by the user is authentic and reliable

Answer: Using getimagesize to determine the type of uploaded images is more reliable than the type of the $_FILES function.

For the same file, the type returned by php using different browsers is different, determined by browsing If the server provides a type type,

may be used by hackers to submit an executable file disguised as an image suffix to the server.

You can use the getimagesize () function to determine the uploaded file type. If it is an avatar file, an array like this will be returned.

Array(
    [0] => 331
    [1] => 234
    [2] => 3
    [3] => width="331" height="234"
    [bits] => 8
    [mime] => image/png

)；

If the getimagesize () function returns an array like this, it will be explained. What is uploaded is the avatar file. The representation type with index 2 is

1 = GIF, 2 = JPG, 3 = PNG, 4 = SWF, 5 = PSD, 6 = BMP, 7 = TIFF (intel byte order), 8 = TIFF( motorola byte order), 9 = JPC, 10 = JP2, 11 = JPX, 12 =JB2, 13 = SWC, 14 = IFF, 15 = WBMP, 16 = XBM,

You can use this to limit Uploaded avatar type

<?php
    $file=$_FILES[&#39;file&#39;];
    if(!empty($file))
    {
       var_dump($file);
       var_dump(getimagesize($file["tmp_name"]));
    }   
?>

7. PHP implements data interaction with Javascript by encoding the URL of the data. However, the encoding and decoding rules for some special characters are different from those of Javascript. Please explain this difference in detail and target the data of the UTF-8 character set. , write the encoding and decoding functions of PHP and the encoding and decoding functions of Javascript to ensure that the PHP encoded data can be correctly decoded by Javascript and the Javascript encoded data can be correctly decoded by PHP

Answer:

<?php
 $str = &#39;思源博客siyuantlw/tlw/sy/俺只是一个打酱油的&#39;;
 $str = iconv("GB2312",&#39;UTF-8&#39;,$str);
 $str = urlencode($str); 
?>

/ /js decodeURIComponent seems to not recognize the GB2312 encoding format and must be converted to utf-8. Then, if there are spaces in the string, it will be converted to numbers

<html>
 <script>
  var ds = &#39;<?php echo $str;?>&#39;;
  var dddd= decodeURIComponent (ds);
  alert(dddd);
 </script>
</html>

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