What is the method for php to return value to the client?

When developing websites, PHP, as a server-side scripting language, often needs to return values ​​to the client to implement certain interactive functions, such as form submission, file upload and download, AJAX asynchronous requests, etc. This article will introduce several common methods for PHP to return values ​​to the client.

1. echo output

In PHP, the most common output method is to output data directly to the client browser through the echo statement. For example, we can output a piece of text to the browser through the following code:

echo "Hello World";
?>

In this way, on the client When you open the page, you can see the browser displays "Hello World".

The echo statement does not terminate the execution of the script like the return statement, but will continue to output until the script ends or an exit or die statement is encountered.

In addition to outputting strings, echo can also output other types of data, such as variables, arrays, objects, etc. For example:

$name = "PHP";
$age = 25;
$arr = array(1, 2, 3);
echo $ name;
echo $age;
print_r($arr);
?>

This way you can output PHP, 25 and [1, 2, 3] to the browser value.

2. json_encode output

In addition to outputting strings, we can also use the json_encode function to convert PHP arrays or objects into JSON format data, and then output it to the browser through echo in the vessel. This method can easily implement scenarios such as AJAX asynchronous requests.

For example, we can first define a PHP array:

$arr = array(

'name' => 'PHP',
'version' => '7.4.23',
'author' => 'The PHP Group'

);
?>
Then use json_encode to convert it to JSON format data and output: 
 header('Content-type: application/json');
 $arr = array(
'name' => 'PHP',
'version' => '7.4.23',
'author' => 'The PHP Group'

);
 echo json_encode($arr);
?>
This will convert the array $arr into {"name":"PHP" ,"version":"7.4.23","author":"The PHP Group"}'s JSON format data is output to the browser. It should be noted that the header function is used here to send the Content-type header information, indicating that the returned data type is JSON. 
header redirection
Another common way is to use the header function for redirection. For example: 
 header("Location: https://www.example.com/");
?>
This is how to execute the script , the browser will automatically jump to the https://www.example.com/ address. 
In addition to using absolute paths, we can also use relative paths for redirection, for example: 
 header("Location: ../index.html" );
?>
The ../ here means returning to the upper-level directory, so it will jump to the index.html page of the upper-level directory. 
It should be noted that the header function must be called before any output, otherwise errors such as "Headers already sent" will occur. 
setcookie Setting Cookie
In addition to returning data to the client, we can also use the setcookie function to set Cookie information. For example: 
 setcookie("username", "admin", time() 3600); // Set cookie, valid for 1 hour
?>
This will set a cookie named username, value admin, and valid for 1 hour in the browser. When the client visits the website again, the server will read the cookie information. 
It should be noted that the setcookie function must be called before any output, and any output cannot be called after the setcookie function. 
Summary
The above four methods are common methods for PHP to return data to the client. Different scenarios require different methods for output. When using header, setcookie and other functions, pay attention to the calling sequence and whether there is output and other issues to avoid unnecessary errors. 
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