std::chrono is used in C to process time, including obtaining the current time, measuring execution time, operation time point and duration, and formatting analysis time. 1. Use std::chrono::system_clock::now() to obtain the current time, which can be converted into a readable string, but the system clock may not be monotonous; 2. Use std::chrono::steady_clock to measure the execution time to ensure monotony, and convert it into milliseconds, seconds and other units through duration_cast; 3. Time point (time_point) and duration (duration) can be interoperable, but attention should be paid to unit compatibility and clock epoch (epoch)

ToaccessenvironmentvariablesinPHP,usegetenv()orthe$_ENVsuperglobal.1.getenv('VAR_NAME')retrievesaspecificvariable.2.$_ENV['VAR_NAME']accessesvariablesifvariables_orderinphp.iniincludes"E".SetvariablesviaCLIwithVAR=valuephpscript.php,inApach

PHPhasthreecommentstyles://,#forsingle-lineand/.../formulti-line.Usecommentstoexplainwhycodeexists,notwhatitdoes.MarkTODO/FIXMEitemsanddisablecodetemporarilyduringdebugging.Avoidover-commentingsimplelogic.Writeconcise,grammaticallycorrectcommentsandu

The method of using preprocessing statements to obtain database query results in PHP varies from extension. 1. When using mysqli, you can obtain the associative array through get_result() and fetch_assoc(), which is suitable for modern environments; 2. You can also use bind_result() to bind variables, which is suitable for situations where there are few fields and fixed structures, and it is good compatibility but there are many fields when there are many fields; 3. When using PDO, you can obtain the associative array through fetch (PDO::FETCH_ASSOC), or use fetchAll() to obtain all data at once, so the interface is unified and the error handling is clearer; in addition, you need to pay attention to parameter type matching, execution of execute(), timely release of resources and enable error reports.

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.

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.

When using PHP preprocessing statements to execute queries with IN clauses, 1. Dynamically generate placeholders according to the length of the array; 2. When using PDO, you can directly pass in the array, and use array_values to ensure continuous indexes; 3. When using mysqli, you need to construct type strings and bind parameters, pay attention to the way of expanding the array and version compatibility; 4. Avoid splicing SQL, processing empty arrays, and ensuring data types match. The specific method is: first use implode and array_fill to generate placeholders, and then bind parameters according to the extended characteristics to safely execute IN queries.

The key steps to install PHP on Windows include: 1. Download the appropriate PHP version and decompress it. It is recommended to use ThreadSafe version with Apache or NonThreadSafe version with Nginx; 2. Configure the php.ini file and rename php.ini-development or php.ini-production to php.ini; 3. Add the PHP path to the system environment variable Path for command line use; 4. Test whether PHP is installed successfully, execute php-v through the command line and run the built-in server to test the parsing capabilities; 5. If you use Apache, you need to configure P in httpd.conf