Detailed explanation of PHP system functions and how to use them

PHP is a powerful server-side scripting language. It has many built-in functions and extension functions, making it easier for developers to code and debug. This article will introduce the PHP system functions and their usage in detail to help readers better learn and apply PHP.

1. Commonly used string functions

1. strlen() function: Returns the length of the string.

Example:

$str = "Hello World!";
echo strlen($str); // 输出 12

2. substr() function: Returns a part of the string.

Example:

$str = "Hello World!";
echo substr($str, 0, 5); // 输出 "Hello"

3. strpos() function: Find a character in a string and return its position.

Example:

$str = "Hello World!";
echo strpos($str, "World"); // 输出 6

4. str_replace() function: Replace a certain character in the string.

Example:

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

2. Commonly used array functions

1. count() function: Returns the length of the array.

Example:

$arr = array(1, 2, 3, 4, 5);
echo count($arr); // 输出 5

2. array_push() function: Add one or more elements to the end of the array.

Example:

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

3. array_pop() function: Pops an element from the end of the array.

Example:

$arr = array(1, 2, 3);
array_pop($arr);
print_r($arr); // 输出 Array ( [0] => 1 [1] => 2 )

4. array_merge() function: Merge two or more arrays into one array.

Example:

$arr1 = array(1, 2, 3);
$arr2 = array(4, 5, 6);
print_r(array_merge($arr1, $arr2)); // 输出 Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 [5] => 6 )

3. Commonly used file processing functions

1. fopen() function: Open a file and return the file pointer.

Example:

$fp = fopen("test.txt", "r");

2. fgets() function: Read a line from the file.

Example:

$fp = fopen("test.txt", "r");
while(!feof($fp)) {
  echo fgets($fp). "<br>";
}
fclose($fp);

3. fwrite() function: writes content to the file.

Example:

$fp = fopen("test.txt", "w");
fwrite($fp, "Hello World!");
fclose($fp);

4. file_get_contents() function: Read the entire file into a string.

Example:

$str = file_get_contents("test.txt");
echo $str;

4. Commonly used date and time functions

1. date() function: format date and time.

Example:

echo date("Y-m-d H:i:s"); // 输出 "2022-01-01 00:00:00"

2. time() function: Returns the Unix timestamp of the current time.

Example:

echo time(); // 输出当前时间的Unix时间戳

3. strtotime() function: Convert a time string into a Unix timestamp.

Example:

echo strtotime("2022-01-01"); // 输出 Unix时间戳

4. mktime() function: Returns the Unix timestamp of a date.

Example:

echo mktime(0, 0, 0, 1, 1, 2022); // 输出 Unix时间戳

5. Commonly used regular expression functions

1. preg_match() function: Match the specified regular expression.

Example:

$str = "Hello World!";
if(preg_match("/World/i", $str)) {
  echo "Match found!";
} else {
  echo "Match not found.";
}

2. preg_replace() function: Replace the matching string with the specified string.

Example:

$str = "Hello World!";
echo preg_replace("/World/i", "PHP", $str);

3. preg_split() function: Split a string using regular expressions.

Example:

$str = "Hello,PHP,World!";
print_r(preg_split("/,/", $str));

6. Commonly used encryption and decryption functions

1. md5() function: Calculate the MD5 hash value of a string.

Example:

$str = "Hello World!";
echo md5($str);

2. sha1() function: Calculates the SHA-1 hash value of a string.

Example:

$str = "Hello World!";
echo sha1($str);

3. base64_encode() function: Encode the string using base64.

Example:

$str = "Hello World!";
echo base64_encode($str);

4. base64_decode() function: Decode a string encoded using base64.

Example:

$str = "SGVsbG8gV29ybGQh";
echo base64_decode($str);

This article only introduces some of the PHP system functions. Readers can continue to learn and study other functions and extension functions of PHP in depth. By learning and using these functions, developers can more easily implement various functions and logic, improving development efficiency and code quality.

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