PHP function learning PHP function comments

1.print_r()
Print easy-to-understand information about the variable. If it is an array, the structural information of the array is displayed.
For example:

. The code is as follows:

$a = array ( 'a' => 'apple', 'b' => 'banana', 'c' => array ('x', 'y', 'z'));
print_r ($a);
?>

axgle comments: Viewing the structural information of any array is an essential tool for program debugging. For any "function" whose return result is an array, just print_r and all the details will be clear at a glance!
2.var_export()
Output or return a string representation of a variable
This function returns structural information about the variable passed to the function. It is similar to print_r(), except that the representation it returns is legal PHP code .
You can return a representation of a variable by setting the second parameter of the function to TRUE.
For example:

. The code is as follows:

$a = array (1, 2, array ("a", "b", "c"));
var_export ($a);
echo "

---

";
$v = var_export($a, TRUE);
echo $v;
?>

axgle comment: In the above example, $v = var_export($a, TRUE ) returns the php code~~ Then you can save it as a php file.
What to do when saving as a php file? Haha, this can be used as a "cache", and you can include it directly when needed.
3.file()
file() returns the file as an array. Each element in the array is a corresponding line in the file, including newlines. On failure file() returns FALSE.

. The code is as follows:

// Read a file into an array.
$lines = file('test.txt');
//View the structure of this array
print_r($lines);
?>

axgle comment: The file() function was my first introduction to php A function that surprised me very much. Compared with the extremely troublesome experience I had in reading and writing files in C language and VB, at that time I felt that there was no more convenient way to read and write files than the file() function.
4.phpinfo()
Print php-related information, such as PHP version, function support, global variables, etc.
For example:
phpinfo();
?>
axgle Comments: A simple function , so that you can always understand the rapid development of PHP---if you pay close attention to the development of PHP~~~~
5.file_get_contents() (Note: PHP 4 >= 4.3.0, PHP 5)
Read the entire file Enter a string. The file_get_contents() function is the preferred method for reading the contents of a file into a string. If the operating system supports it, memory mapping technology will also be used to enhance performance.
For example:
$data = file_get_contents('test.txt');
echo $data;
?>
6. file_put_contents (Note: PHP 5)
Write a string directly to the file.
For example:
//The address of an image
$url="http://...test.com/plmm.jpg";
//Read binary "string"
$data =file_get_contents($url);
//Save to your computer
file_put_contents("Beauty.jpg",$data);
?>
axgle Comments: If you find that the pictures on a certain beauty picture website are named something like 1.jpg, 2.jpg...
ok, use a for loop to catch all the "beauties", don't get too excited and make your girlfriend
jealous~~~
7.function_exists
If If the function exists, return true
For example:
//If the function does not exist, customize the function
if(!function_exists('file_put_contents')) {
function file_put_contents($filename,$data) {
$fp=fopen($filename,"wb");
fwrite($fp,$data);
fclose($fp);
}
}
?>
8.get_defined_functions
Return an array and get All defined php functions.
For example:

. The code is as follows:

$arr = get_defined_functions();
print_r($arr);
?>

axgle comments: Now you know all the functions It's famous. If you want to know the usage of a certain function, you can use the form http://www.php.net/function_name to check online. "Cure all diseases, diagnose all kinds of difficult problems, and cure the disease~~~~"
9.get_declared_classes
Returns an array to get all defined php classes.
For example:

. The code is as follows:

$arr = get_declared_classes();
print_r($arr);
?>

axgle comments: I believe you can see this function after running Example 8. When you run this function in php4, you can only get a few classes; but if you use php5, you will see dozens of predefined php classes in this example! It can be seen that php5 has been enhanced a lot in object-oriented aspects.
10.exit
Output the message and stop the current script. (Note: Like echo, this is not a "function", but a "statement").
For example:
echo "Statement 1";
exit("The following statement 2 will not be output");
echo "Statement 2";
?>
axgle comments: debug the program and find the errors Location, etc. are more useful.
There are many more useful PHP functions, and there are some very interesting PHP functions to share. I will introduce them when I have time.

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