What are the commonly used PHP functions and their application scenarios?

PHP provides a rich function library, including: string operation functions: getting length, converting case, replacing characters, and splitting strings. Mathematical functions: Obtain absolute values, round, find maximum and minimum values, and calculate powers. Date and time functions: display current time, return timestamp, convert strings, calculate date differences. File system functions: Open, read, write, delete files. Practical scenario: Verify whether the username is between 5 and 15 characters, and use the strlen() function to determine the length.

Commonly used functions in PHP and their application scenarios

PHP provides a rich function library that can be used for various programming tasks . The following are several commonly used functions and their application scenarios:

String operation function

• strlen(): Get String length. Application: Verify that user input meets length requirements.
• strtoupper(): Convert the string to uppercase. Application: Processing fields that require capitalization such as names of people and places.
• strtolower(): Convert the string to lowercase. Application: Handling fields that require lowercase such as password hashes and search queries.
• str_replace(): Replace the specified character or substring in the string. Applications: filtering dirty data and creating dynamic content.
• explode(): Split the string into an array. Application: Parsing URLs, text files, and CSV files.

Mathematical functions

• abs(): Get the absolute value of a number. Application: Calculate the distance or size of numbers.
• round(): Round the number. Applications: Rounding monetary values ​​and calculating averages.
• max() and min(): Return the maximum or minimum value in an array or set of numbers. Application: Determine maximum or minimum values.
• pow(): Calculate the power of a number. Applications: Calculating compound interest and solving algebraic equations.

Date and time functions

• date(): Display the current date and time in a specific format. Application: Generate timestamps and manage log files.
• time(): Returns the Unix timestamp. Application: Record the moment when an event occurs and create an expiration mechanism.
• strtotime(): Convert date and time strings to Unix timestamps. Application: Process user-entered dates and times.
• date_diff(): Calculate the difference between two dates. Application: Calculate age, order execution time and activity duration.

File system functions

• fopen(): Open a file for reading or writing. Application: Process text files, images and uploads.
• fread(): Read data from the file. Application: Load content from files and extract specific parts.
• fwrite(): Write data to the file. Application: Save log information and generate reports.
• unlink(): Delete the file. Application: Clean temporary files and enforce file security policies.

Practical case: verify user input

// 获取用户输入的用户名
$username = $_POST['username'];

// 验证用户名是否有效（长度在 5 到 15 个字符之间）
if (strlen($username) < 5 || strlen($username) > 15) {
    // 用户名无效
    echo '用户名必须在 5 到 15 个字符之间';
}

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