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.

There are two main ways to get the last N characters of a string in PHP: 1. Use the substr() function to intercept through the negative starting position, which is suitable for single-byte characters; 2. Use the mb_substr() function to support multilingual and UTF-8 encoding to avoid truncating non-English characters; 3. Optionally determine whether the string length is sufficient to handle boundary situations; 4. It is not recommended to use strrev() substr() combination method because it is not safe and inefficient for multi-byte characters.

To set and get session variables in PHP, you must first always call session_start() at the top of the script to start the session. 1. When setting session variables, use $_SESSION hyperglobal array to assign values ??to specific keys, such as $_SESSION['username']='john_doe'; it can store strings, numbers, arrays and even objects, but avoid storing too much data to avoid affecting performance. 2. When obtaining session variables, you need to call session_start() first, and then access the $_SESSION array through the key, such as echo$_SESSION['username']; it is recommended to use isset() to check whether the variable exists to avoid errors

Execution of SELECT queries using PHP's preprocessing statements can effectively prevent SQL injection and improve security. 1. Preprocessing statements separate SQL structure from data, send templates first and then pass parameters to avoid malicious input tampering with SQL logic; 2. PDO and MySQLi extensions commonly used in PHP realize preprocessing, among which PDO supports multiple databases and unified syntax, suitable for newbies or projects that require portability; 3. MySQLi is specially designed for MySQL, with better performance but less flexibility; 4. When using it, you should select appropriate placeholders (such as? or named placeholders) and bind parameters through execute() to avoid manually splicing SQL; 5. Pay attention to processing errors and empty results to ensure the robustness of the code; 6. Close it in time after the query is completed.

How to quickly create new emails in Outlook is as follows: 1. The desktop version uses the shortcut key Ctrl Shift M to directly pop up a new email window; 2. The web version can create new emails in one-click by creating a bookmark containing JavaScript (such as javascript:document.querySelector("divrole='button'").click()); 3. Use browser plug-ins (such as Vimium, CrxMouseGestures) to trigger the "New Mail" button; 4. Windows users can also select "New Mail" by right-clicking the Outlook icon of the taskbar

Optional can clearly express intentions and reduce code noise for null judgments. 1. Optional.ofNullable is a common way to deal with null objects. For example, when taking values ??from maps, orElse can be used to provide default values, so that the logic is clearer and concise; 2. Use chain calls maps to achieve nested values ??to safely avoid NPE, and automatically terminate if any link is null and return the default value; 3. Filter can be used for conditional filtering, and subsequent operations will continue to be performed only if the conditions are met, otherwise it will jump directly to orElse, which is suitable for lightweight business judgment; 4. It is not recommended to overuse Optional, such as basic types or simple logic, which will increase complexity, and some scenarios will directly return to nu.

To extract substrings from PHP strings, you can use the substr() function, which is syntax substr(string$string,int$start,?int$length=null), and if the length is not specified, it will be intercepted to the end; when processing multi-byte characters such as Chinese, you should use the mb_substr() function to avoid garbled code; if you need to intercept the string according to a specific separator, you can use exploit() or combine strpos() and substr() to implement it, such as extracting file name extensions or domain names.