To safely handle PHP file uploads, you need to verify the source and type, control the file name and path, set server restrictions, and process media files twice. 1. Verify the upload source to prevent CSRF through token and detect the real MIME type through finfo_file using whitelist control; 2. Rename the file to a random string and determine the extension to store it in a non-Web directory according to the detection type; 3. PHP configuration limits the upload size and temporary directory Nginx/Apache prohibits access to the upload directory; 4. The GD library resaves the pictures to clear potential malicious data.

InPHP,variablesarepassedbyvaluebydefault,meaningfunctionsorassignmentsreceiveacopyofthedata,whilepassingbyreferenceallowsmodificationstoaffecttheoriginalvariable.1.Whenpassingbyvalue,changestothecopydonotimpacttheoriginal,asshownwhenassigning$b=$aorp

AgeneratorinPHPisamemory-efficientwaytoiterateoverlargedatasetsbyyieldingvaluesoneatatimeinsteadofreturningthemallatonce.1.Generatorsusetheyieldkeywordtoproducevaluesondemand,reducingmemoryusage.2.Theyareusefulforhandlingbigloops,readinglargefiles,or

The reason why header('Location:...') in AJAX request is invalid is that the browser will not automatically perform page redirects. Because in the AJAX request, the 302 status code and Location header information returned by the server will be processed as response data, rather than triggering the jump behavior. Solutions are: 1. Return JSON data in PHP and include a jump URL; 2. Check the redirect field in the front-end AJAX callback and jump manually with window.location.href; 3. Ensure that the PHP output is only JSON to avoid parsing failure; 4. To deal with cross-domain problems, you need to set appropriate CORS headers; 5. To prevent cache interference, you can add a timestamp or set cache:f

To prevent session hijacking in PHP, the following measures need to be taken: 1. Use HTTPS to encrypt the transmission and set session.cookie_secure=1 in php.ini; 2. Set the security cookie attributes, including httponly, secure and samesite; 3. Call session_regenerate_id(true) when the user logs in or permissions change to change to change the SessionID; 4. Limit the Session life cycle, reasonably configure gc_maxlifetime and record the user's activity time; 5. Prohibit exposing the SessionID to the URL, and set session.use_only

The urlencode() function is used to encode strings into URL-safe formats, where non-alphanumeric characters (except -, _, and .) are replaced with a percent sign followed by a two-digit hexadecimal number. For example, spaces are converted to signs, exclamation marks are converted to!, and Chinese characters are converted to their UTF-8 encoding form. When using, only the parameter values ??should be encoded, not the entire URL, to avoid damaging the URL structure. For other parts of the URL, such as path segments, the rawurlencode() function should be used, which converts the space to . When processing array parameters, you can use http_build_query() to automatically encode, or manually call urlencode() on each value to ensure safe transfer of data. just

In PHP, you can use square brackets or curly braces to obtain string specific index characters, but square brackets are recommended; the index starts from 0, and the access outside the range returns a null value and cannot be assigned a value; mb_substr is required to handle multi-byte characters. For example: $str="hello";echo$str[0]; output h; and Chinese characters such as mb_substr($str,1,1) need to obtain the correct result; in actual applications, the length of the string should be checked before looping, dynamic strings need to be verified for validity, and multilingual projects recommend using multi-byte security functions uniformly.

You can use substr() or mb_substr() to get the first N characters in PHP. The specific steps are as follows: 1. Use substr($string,0,N) to intercept the first N characters, which is suitable for ASCII characters and is simple and efficient; 2. When processing multi-byte characters (such as Chinese), mb_substr($string,0,N,'UTF-8'), and ensure that mbstring extension is enabled; 3. If the string contains HTML or whitespace characters, you should first use strip_tags() to remove the tags and trim() to clean the spaces, and then intercept them to ensure the results are clean.