What books are recommended for learning PHP functions?

PHP functions are reusable blocks of code that provide functionality to perform common tasks, such as: printing variable contents (print_r(), var_dump()) converting string case (strtoupper(), strtolower()) removing string spaces (trim()) Convert date string to timestamp (strtotime()) User-definable function, defined through function keyword

Use PHP function Guidelines

PHP functions are reusable blocks of code that accept incoming parameters, perform a specific operation and return a result. They can greatly simplify the development process and help ensure code maintainability.

Core PHP Functions

Core PHP Functions is a large and growing library that provides a set of functions for performing common tasks. Some of the most commonly used core functions include:

• print_r(): Prints the contents of a variable, including its type and structure.
• var_dump(): Print variables in a more detailed and formatted way.
• strtoupper(): Convert the string to uppercase letters.
• strtolower(): Convert the string to lowercase letters.
• trim(): Remove spaces from the beginning and end of the string.
• strtotime(): Convert string date and time to Unix timestamp.

User-Defined Functions

In addition to the core functions, you can also create your own custom functions. Custom functions are defined with the function keyword, followed by the function name, parameter list, and function body:

function myFunction($param1, $param2) {
  // 函数体
}

A function can be called by calling the function name and passing the necessary parameters:

$result = myFunction('a', 'b');

Practical Example: Validating User Input

PHP functions can be used for a wide range of development tasks, including form validation. Let's say you have a form that collects users' names and email addresses. You can use a PHP function to verify that the user entered non-empty and well-formatted input:

function validateInput($name, $email) {
  if (empty($name) || empty($email)) {
    return false;
  }
  if (! filter_var($email, FILTER_VALIDATE_EMAIL)) {
    return false;
  }
  return true;
}

$valid = validateInput($_POST['name'], $_POST['email']);

$valid is true if the input is valid, otherwise false.

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