[Summary] Some commonly used built-in functions in PHP

As a widely used programming language, PHP has many built-in functions available. During the coding process, mastering these functions allows developers to write code more quickly and efficiently. This article will explore some of the commonly used functions in PHP.

1. String processing function

1. strlen(string $string): Get the string length
   This function will return the length of the given string. For example:

$str = "Hello, world!";
echo strlen($str); // 输出：13

2. strpos(string $haystack, mixed $needle [, int $offset = 0]): Find the first occurrence of the substring in the string
   The The function returns the position of the first occurrence of the specified substring in the given string. If the substring is not found, returns FALSE. For example:

$str = "Hello, world!";
echo strpos($str, "world"); // 输出：7

3. str_replace(mixed $search , mixed $replace , mixed $subject [, int &$count ]): Replace the substring in the string
   This function will Returns a new string in which all strings matching $search are replaced with the $replace string. For example:

$str = "Hello, world!";
echo str_replace("world", "PHP", $str); // 输出：Hello, PHP!

2. Array processing function

1. count(mixed $array_or_countable [, int $mode = COUNT_NORMAL]): Returns the number of elements in the array
   This function returns the number of elements in the array. For example:

$arr = [1, 2, 3];
echo count($arr); // 输出：3

2. array_push(array &$array , mixed $value1 [, mixed $... ]): Push one or more elements to the end of the array
   This function Appends one or more elements to the end of the given array, returning the number of elements in the new array. For example:

$arr = [1, 2, 3];
echo array_push($arr, 4, 5); // 输出：5
print_r($arr); // 输出：Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 )

3. array_merge(array $array1 [, array $... ]): Merge one or more arrays
   This function merges two or more arrays into a new array. For example:

$arr1 = [1, 2, 3];
$arr2 = [4, 5];
print_r(array_merge($arr1, $arr2)); // 输出：Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 )

3. File processing function

1. file_get_contents(string $filename [, bool $use_include_path = FALSE [, resource $context [, int $offset = - 1 [, int $maxlen = -1 ]]]]): Read the entire file into a string
   This function reads the contents of the specified file into a string. For example:

$file_str = file_get_contents("./test.txt");
echo $file_str;

2. file_put_contents(string $filename , mixed $data [, int $flags = 0 [, resource $context ]]): Write a string to the file
   This function writes the specified string to the specified file. For example:

$data = "Hello, world!";
file_put_contents("./test.txt", $data);

4. scandir(string $directory [, int $sorting_order = SCANDIR_SORT_ASCENDING [, resource $context ]]): Returns the files and directories in the specified directory
   This function will Returns all files and directories in the specified directory. For example:

$files = scandir("./");
print_r($files);

The above are only some basic functions built into PHP. In the process of using PHP, other more complex functions and components will also be involved. Understanding and becoming familiar with these functions will help developers develop PHP applications more quickly and efficiently.

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