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  • What is the child combinator (>) in CSS selectors?
    What is the child combinator (>) in CSS selectors?
    Thechildcombinator(>)inCSSselectsonlydirectchildrenofaspecifiedelement,unlikedescendantselectorsthattargetallnestedelements.1.Itensuresstylesapplyexclusivelytoimmediatechildren,suchastop-levellistitemsinanavigationmenu.2.Thiscombinatorisusefulford
    CSS Tutorial . Web Front-end 541 2025-07-09 02:15:30
  • Debugging CSS specificity and inheritance issues
    Debugging CSS specificity and inheritance issues
    When encountering problems such that the CSS style does not take effect, is overwritten or inheritance confusing, the CSS feature value and inheritance mechanism should be given priority. 1. Understand and calculate the specific weight of the selector, inline style > ID selector > Class selector, attribute selector, pseudo-class > element selector and pseudo-element. Rules with high weights will override the rules with low weights, even if the latter appears in the code; you can view the style source and weights through the "Computed" panel of the browser developer tool. 2. Avoid abuse!important, only used when covering third-party library styles or emergency repairs. It is also recommended to optimize the structure by increasing the selector weight, splitting the class, or adopting BEM naming specifications. 3. Pay attention to whether the attributes are
    CSS Tutorial . Web Front-end 714 2025-07-09 02:11:20
  • how to fix undefined index in PHP
    how to fix undefined index in PHP
    When encountering the "undefinedindex" error in PHP, the solutions include: 1. Use isset() to determine whether the index exists and avoid directly accessing undefined keys; 2. Use array_key_exists() to check whether the key exists, which is suitable for situations where null values ??need to be distinguished; 3. Set default values ??for variables, such as using the empty merge operator?? to improve the simplicity of the code; 4. Turn on error reports to help locate problems. These practices can effectively prevent errors caused by accessing non-existent array keys, and improve code robustness and maintainability.
    PHP Tutorial . Backend Development 133 2025-07-09 02:08:21
  • mysql error 1045 access denied for user 'root'@'localhost'
    mysql error 1045 access denied for user 'root'@'localhost'
    I encountered MySQL error 1045: Accessdeniedforuser'root'@'localhost', indicating that authentication failed when connecting to the database. Common reasons and solutions are as follows: 1. Check whether the user name and password are correct. It is recommended to use sudomysql-uroot to log in without password; 2. Confirm that the MySQL service has been started, and you can check and start the service through systemctl or brewservices; 3. Check the permission configuration, confirm the bind-address and skip-networking settings, and ensure that the root user is allowed to log in from the corresponding host; 4. If you forget your password, you can deactivate MySQL and
    Mysql Tutorial . Database 373 2025-07-09 02:07:01
  • PHP trim characters from a string
    PHP trim characters from a string
    PHP's trim() function can be used to remove whitespace characters or other specified characters at the beginning and end of a string. 1. By default, trim() removes spaces, tab characters (\t), line breaks (\n), carriage return characters (\r), empty bytes (\0), and vertical tab characters (\x0B); for example, trim("\n\tHelloWorld!\r\n") outputs HelloWorld! 2. The characters to be removed can be specified through the second parameter, such as trim("---HelloWorld!---","-") returns HelloWorld!, and supports multiple characters, such as trim(&
    PHP Tutorial . Backend Development 241 2025-07-09 02:06:40
  • PHP session security best practices
    PHP session security best practices
    To ensure the security of Session in PHP, the following measures must be taken: 1. Use a strong random SessionID and enable strict mode; 2. Enable HTTPS and set the Secure and HttpOnly flags; 3. Change the SessionID regularly; 4. Prevent SessionFixation and Hijacking. Specific practices include configuring session.entropy_file and session.use_strict_mode, checking the ID legality before session_start(), setting cookie parameters to ensure HTTPS transmission and prohibiting JS access, and calling session_regen after logging in
    PHP Tutorial . Backend Development 698 2025-07-09 02:06:21
  • how to create an associative php array
    how to create an associative php array
    The key to creating an associative array in PHP is to use strings as keys. 1. You can directly assign values ??to create using square brackets or array() functions, such as $user=['name'=>'Tom','age'=>25]; 2. You can also add elements dynamically, such as $user['gender']='male'; 3. You can also generate results through database query, such as using PDO's fetchAll(PDO::FETCH_ASSOC) method; common errors include spelling errors in key names, not adding quotes, and duplication of key names, resulting in overwriting of values.
    PHP Tutorial . Backend Development 777 2025-07-09 02:05:40
  • Utilizing CSS calc() function for dynamic sizing
    Utilizing CSS calc() function for dynamic sizing
    TheCSScalc()functionallowsdynamicsizingofwebpageelementsbyperformingmathematicaloperationsinstylesheets.Itenablesflexibilitybymixingunitslike%,px,em,andrem,andrecalculatesvaluesonthefly.1.Itisusefulforresponsivelayouts,suchassettingwidthwithspacingad
    CSS Tutorial . Web Front-end 401 2025-07-09 02:04:01
  • What is the Difference Between `die()` and `exit()` in PHP?
    What is the Difference Between `die()` and `exit()` in PHP?
    InPHP,die()andexit()arefunctionallyidentical.1.Bothfunctionsterminatescriptexecutionimmediately.2.Theycanacceptastringmessageoranintegerstatuscodeasanargument,wherestringsareoutputtedbeforeterminationandintegerssettheexitstatus.3.die()istechnicallyan
    PHP Tutorial . Backend Development 262 2025-07-09 02:03:41
  • What is the html canvas element used for?
    What is the html canvas element used for?
    Elements of HTML are used to render graphics on web pages through JavaScript. They do not have the ability to display shapes or images themselves and must be drawn through scripts. 1. It supports drawing basic shapes such as rectangles, circles and lines. Common methods include fillingRect() filling rectangles, strokeRect() stroke rectangles and clearRect() clear areas; 2. It can render images and text, use drawImage() to place images, fillText() to draw text; 3. It is suitable for animation and real-time graphics, and the animation effect is achieved through repeated clearing and redrawing, and can be optimized with requestAnimationFrame(); 4. The disadvantage is that the content is inaccessible and unsuitable.
    HTML Tutorial . Web Front-end 946 2025-07-09 01:59:52
  • mysql show grants for user
    mysql show grants for user
    To view MySQL user permissions, use the SHOWGRANTS command, the syntax is SHOWGRANTSFOR'user'@'hostname'; for example, SHOWGRANTSFOR'test_user'@'localhost'; you can view the local connection user permissions; if the host name is not determined, you can use % wildcard instead. In the execution results, USAGE means no actual permissions, SELECT, INSERT, etc. are common operation permissions, and the content after ON indicates the scope of the permissions, such as mydb.* means all objects under the mydb database. This command is suitable for troubleshooting permission problems, permission migration and copying, and avoiding misdeletion of permissions. Notes include: The username and master must be matched accurately
    Mysql Tutorial . Database 678 2025-07-09 01:59:11
  • how to simulate full outer join in mysql
    how to simulate full outer join in mysql
    MySQL does not support FULLOUTERJOIN, and can be implemented through LEFTJOIN and RIGHTJOIN combined with UNION. 1. Use LEFTJOIN and RIGHTJOIN joint query, merge and deduplication through UNION, pay attention to the consistent order of the fields; 2. Use COALESCE to unify the primary key when processing duplicate data, which is convenient for subsequent processing; 3. For complex scenarios, temporary tables or subqueries can be used to process the left and right table data separately and then merge them to improve readability. The core is to merge left and right results and remove heavy weights.
    Mysql Tutorial . Database 456 2025-07-09 01:56:41
  • mysql too many connections error
    mysql too many connections error
    When MySQL error occurs, the following steps can be solved through the following steps: 1. Log in to MySQL to execute SHOWSTATUSLIKE'Threads_connected' and SHOWVARIABLESLIKE'max_connections' to confirm whether the number of connections exceeds the limit; 2. Check whether there is a prompt for "Toomyconnections" in the log; 3. Temporarily increase the max_connections value and take effect by dynamically setting or modifying the configuration file; 4. Check PROCESSLIST and KILL to release idle connections; 5. Long-term optimization includes reasonably configuring the connection pool parameters,
    Mysql Tutorial . Database 379 2025-07-09 01:55:40
  • What is the tabindex attribute and how does it affect focus order?
    What is the tabindex attribute and how does it affect focus order?
    Thetabindexattributecontrolselementfocusbehavior.Negativevalues(e.g.,-1)allowprogrammaticfocusbutexcludefromtabbing,zero(0)includestheelementinthenaturaltaborder,andpositivevaluesdefineacustomtaborderbutshouldbeavoidedunlessnecessary.Usetabindex=&quo
    HTML Tutorial . Web Front-end 804 2025-07-09 01:54:21

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