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  • how to avoid undefined index error in PHP
    how to avoid undefined index error in PHP
    There are three key ways to avoid the "undefinedindex" error: First, use isset() to check whether the array key exists and ensure that the value is not null, which is suitable for most common scenarios; second, use array_key_exists() to only determine whether the key exists, which is suitable for situations where the key does not exist and the value is null; finally, use the empty merge operator?? (PHP7) to concisely set the default value, which is recommended for modern PHP projects, and pay attention to the spelling of form field names, use extract() carefully, and check the array is not empty before traversing to further avoid risks.
    PHP Tutorial . Backend Development 653 2025-07-14 02:51:21
  • php microtime as float
    php microtime as float
    To get microtime as float, the call method is $currentTime=microtime(true); which returns a floating point number containing seconds and microseconds. 1. Use microtime(true) to directly obtain floating point numbers in seconds, which is suitable for performance analysis and execution time statistics; 2. Compared with the default return string format, float is more convenient for mathematical operations; 3. You can record the time difference of the time by recording the code through $start and $end; 4. Pay attention to floating point accuracy, time unit conversion and avoid high-frequency calls when using it; 5. Common application scenarios include script execution time statistics, interface response monitoring, logging and timing task control. micro
    PHP Tutorial . Backend Development 578 2025-07-14 02:51:01
  • PHP preg_replace to replace only N occurrences
    PHP preg_replace to replace only N occurrences
    To limit the number of replacements for preg_replace in PHP, it can be achieved by setting its fourth parameter $limit, which specifies the maximum number of replacements per match. For example, setting $limit to 2 means replacing only the content of the first two matches; for more complex requirements such as replacing the third match, preg_replace_callback combined with counter logic is required.
    PHP Tutorial . Backend Development 225 2025-07-14 02:47:50
  • PHP session lifetime and expiration
    PHP session lifetime and expiration
    To set the expiration time of PHPsession, you need to adjust the two parameters of session.gc_maxlifetime and session.cookie_lifetime; 1.session.gc_maxlifetime controls the retention time of the server session data, the default is 1440 seconds (24 minutes); 2.session.cookie_lifetime controls the validity period of the client cookie, the default is 0 (it is invalid if the browser is closed); it can be set globally in php.ini or dynamically configured using ini_set in the code; the "expiration" of session is triggered by the garbage collection mechanism and is not cleaned up regularly.
    PHP Tutorial . Backend Development 627 2025-07-14 02:46:31
  • PHP check if a string starts with a specific string
    PHP check if a string starts with a specific string
    In PHP, you can use a variety of methods to determine whether a string starts with a specific string: 1. Use strncmp() to compare the first n characters. If 0 is returned, the beginning matches and is not case sensitive; 2. Use strpos() to check whether the substring position is 0, which is case sensitive. Stripos() can be used instead to achieve case insensitive; 3. You can encapsulate the startsWith() or str_starts_with() function to improve reusability; in addition, it is necessary to note that empty strings return true by default, encoding compatibility and performance differences, strncmp() is usually more efficient.
    PHP Tutorial . Backend Development 354 2025-07-14 02:44:30
  • How does PHP session garbage collection work?
    How does PHP session garbage collection work?
    PHPsessiongarbagecollection cleans old session data, triggers by default through the probability mechanism, and uses session.gc_probability and session.gc_divisor to set the trigger probability. For example, 1/100 is triggered, 1% request is triggered. The session retention time is controlled by session.gc_maxlifetime. If it is not accessed for 24 minutes by default, it is suitable for file storage methods. Common problems include untimely cleaning of low-traffic sites, errors in path permissions, and shared hosting restrictions. It is recommended to optimize management with cron tasks or custom processors.
    PHP Tutorial . Backend Development 283 2025-07-14 02:43:11
  • PHP undefined index $_GET
    PHP undefined index $_GET
    The PHPUndefinedIndex:$_GET error is because the unpassed GET parameter key is accessed. The error occurs when trying to read a parameter that does not exist in the URL, for example using echo$_GET['id'] but the URL does not have?id=123. Avoiding methods include: 1. Use isset($_GET['id']) to determine whether the key exists; 2. Use the ternary operator to set the default value such as $id=isset($_GET['id'])? $_GET['id']:null; 3. Choose whether to use empty() or array_key_exists() according to your needs. Development suggestions include: not directly use unverified parameters and unification
    PHP Tutorial . Backend Development 804 2025-07-14 02:39:51
  • PHP undefined index after json_decode
    PHP undefined index after json_decode
    The problem with PHPundefinedindexafterjson_decode occurs mainly because of accessing non-existent keys. 1. Ensure that json_decode is executed correctly, check the JSON string format and use json_last_error() to determine whether the parsing is successful; 2. Use isset() or array_key_exists() to check whether it exists before accessing the key. The nested structure needs to be judged layer by layer; 3. Debug the output data structure through var_dump() or print_r() to confirm that the key name, hierarchy and type are correct; 4. Use the null merge operator?? to set the default value to avoid undefined index errors, improve code security and
    PHP Tutorial . Backend Development 253 2025-07-14 02:38:51
  • PHP convert ASCII value to character using chr
    PHP convert ASCII value to character using chr
    In PHP, using the chr() function can convert the ASCII value to the corresponding character. 1.chr() receives an integer parameter (ASCII code) and returns the corresponding characters; 2. The valid range is 0 to 127, and the results outside this range may vary from system to system; 3. Common uses include generating line breaks (chr(10)), carriage return (chr(13)), tab characters (chr(9)) and spaces (chr(32)); 4. Notes: Floating point numbers will be truncated, multi-byte characters need to be processed by mb_ function, and some ASCII codes have no visual output.
    PHP Tutorial . Backend Development 643 2025-07-14 02:38:10
  • php iterate over a date range
    php iterate over a date range
    It is recommended to use the DatePeriod class to traverse date ranges in PHP. 1. The DatePeriod class was introduced from PHP5.3, and date traversal is implemented by setting the start date, end date and interval. For example, generate a date list from 2024-01-01 to 2024-01-05, which does not include the end date by default; 2. If you need to include the end date, you can adjust the end date or set the INCLUDE_END_DATE parameter; 3. The manual loop method can also complete the traversal using the DateTime object and the modify() method, which is suitable for scenarios where step size needs to be flexibly controlled; 4. Pay attention to the time zone problem that should be explicitly set to avoid the system's default time zone affecting the result; 5. PHP automatically handles leap years
    PHP Tutorial . Backend Development 168 2025-07-14 02:37:50
  • PHP prepared statement example
    PHP prepared statement example
    Preprocessing statements can effectively prevent SQL injection and improve execution efficiency in PHP database operations. When inserting data using MySQLi, use prepare() to define the statement, bind_param() to bind parameters. After multiple executions, you only need to modify and change the variable and call execute(); when querying, use prepare() and bind_param() to pass parameters, and then bind the result variables through bind_result() and obtain data with fetch(); if PDO is used, similar functions can be achieved through named parameters and array parameters, such as prepare() and pass parameters with execute(), and pass parameters through fetch(PDO::FETCH_ASSOC
    PHP Tutorial . Backend Development 855 2025-07-14 02:36:21
  • What is Dependency Injection and why is it important in php development?
    What is Dependency Injection and why is it important in php development?
    DependencyInjection(DI)solvestightcouplinginPHPcodebyallowingexternalinjectionofdependencies,improvingflexibilityandtestability.Insteadofclassescreatingorlocatingtheirowndependencies,theyreceivethemfromoutside,makingiteasiertoswapimplementations,usem
    PHP Tutorial . Backend Development 577 2025-07-14 02:34:20
  • What is the difference between a function expression and a function declaration in PHP?
    What is the difference between a function expression and a function declaration in PHP?
    The main difference between function expressions and function declarations in PHP is to improve behavior and usage scenarios. Function declarations start with the function keyword, will be promoted and can be called before definition; suitable for scenarios where scripts are available anywhere, no conditional definition is required, and top-down readability is required. Function expressions assign functions to variables and will not be promoted. They must be defined first and then called; they are suitable for scenarios where conditions require the creation, use of closures or anonymous functions and are passed as parameters. The two are the same in terms of functional characteristics, but the creation and access timing are different.
    PHP Tutorial . Backend Development 489 2025-07-14 02:34:01
  • how to deep copy a php array
    how to deep copy a php array
    There are three ways to implement deep copy of arrays in PHP: First, use unserialize and serialize to disconnect references by serializing and deserializing, which is suitable for ordinary and nested arrays; second, object arrays combine clone and recursive functions to flexibly process mixed types but ensure that the class supports correct cloning; third, json_encode and json_decode are suitable for pure scalar data, with simple writing but no resources or special objects.
    PHP Tutorial . Backend Development 980 2025-07-14 02:24:20

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