What is a php custom function? Detailed explanation of the concept of php custom functions

Before introducing what is a PHP custom function, let us first introduce what a function is.

Function is a form in which statements with certain functions are organized together to define a function. The purpose is to divide the program into functional blocks to facilitate the use, management, reading and debugging of the program.

There are two types of functions:

One is a function written by others or provided internally by the system. As long as you know what this function is used for, you can recognize it yourself. Just use it. There is no need to delve into how the function is implemented. For example, the various string functions and array functions that have been used have the following characteristics:

1. They can all perform some specific functions

2. All have special names

3. All have more or less parameters

4. Most functions will have a return value, and even if not, they will execute a specific Operation

5. No need to know the internal implementation logic of the function

Another type of function is defined by oneself to realize one's own unique needs. The concept may be abstract and difficult to understand. We can imagine the function as a juicer, the parameters are like the fruits we put in, and the code executed in the function is like the stirring of the blender. The parameters returned are different, and the results returned by the function are also different, just like apple juice will not come out after adding oranges. Functions can also accept multiple parameters, just like mixed juice.

The function only leaves us with the function name to call, and we do not need to understand how the code in the function is defined. Similarly, we do not need to understand the working principle of the juicer. Functions exist in most programming languages ​​and are used to separate pieces of code that perform independent, well-defined tasks. Function names must start with a letter or an underscore, followed by letters, numbers, or underscores. In addition, function names are case-insensitive.

So the definition of a function is a named, independent piece of code that performs a specific task and may return a value to the program that calls it. PHP's modular program structure is implemented through functions or objects. Functions divide complex PHP programs into several functional modules. Each module is written into a PHP function, and then the function is called in the script, and Call functions within functions to implement some large PHP scripting.

Generally, PHP's built-in functions are used. However, the real functionality of a programming language is achieved by creating your own functions. Most of the functions provided by PHP are basic functions, such as operating arrays, accessing databases, reading and writing files, etc. However, in real projects, PHP functions cannot meet our needs. We cannot find functions that can be used to process contracts, calculate attendance rates, or print data tables.

During the development process, certain operations often need to be repeated, such as data query, character manipulation, etc. If the code needs to be re-entered for each module operation, it will not only cause the programmer a huge headache, but also It also has a great impact on the later maintenance and operation effects of the code. Fortunately, we are not limited to PHP built-in functions. We can write our own functions to complete any task. This is a custom function.

When writing a function, you must first clarify what you want the function to do, what purpose it achieves, and what functions it wants to achieve. After knowing these, your thinking will be clear when writing, and the code will be easier to write. It won't feel too difficult. In PHP, in addition to the thousands of system functions that friends can use directly, you can also create custom functions according to your own module needs.

The so-called system functions are functions provided in PHP that can be used directly. Each system function is a complete code segment that can complete the specified task. The more you learn one of the system functions, the more you will master one more PHP function. During the development process, some commonly used functions can be completed by calling system functions. If some functional modules do not provide system functions in PHP, you need to define the functions yourself. To complete the same task, system functions are generally more efficient than custom functions, but there is no obvious difference in how the two functions are called in the program.

php custom functions have the following advantages:

a. The program can be reused

b. Improve code maintainability

c. Improve development efficiency

d. Greatly enhance reliability

e. Control the complexity of program design

The following is a simple PHP custom function output example

<?php
 function pr(){
  echo "这是个自定义函数";
 }
  pr();
?>

The output result: This is a custom function

The above is an introduction to PHP custom functions , the next chapter will explain how to declare PHP custom functions with examples.

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