This post covers the JSON and AJAX section of the Data Formats and Types chapter when studying for the Zend PHP 7 Certification.
JSON is an acronym for JavaScript Object Notation and it is a lightweight data-interchange format. PHP provides a JSON extension that is enabled by default, and contains some useful functions to use.
The first function to look at, json_decode(), takes a JSON encoded string and converts it into a PHP variable.
By default, the function returns a PHP object, however it can return an associative array if the second parameter (called assoc) is set to true.
<?php
$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';
var_dump(json_decode($json));
var_dump(json_decode($json, true));
// Outputs:
object(stdClass)#1 (5) {
["a"] => int(1)
["b"] => int(2)
["c"] => int(3)
["d"] => int(4)
["e"] => int(5)
}
array(5) {
["a"] => int(1)
["b"] => int(2)
["c"] => int(3)
["d"] => int(4)
["e"] => int(5)
}json_encode() returns a string containing the JSON representation of value.
<?php
$arr = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5);
echo json_encode($arr);
// Outputs:
{"a":1,"b":2,"c":3,"d":4,"e":5}
$d = array('foo' => 'bar', 'baz' => 'long');
echo "Associative array always output as object: ", json_encode($d), "\n";
echo "Associative array always output as object: ", json_encode($d, JSON_FORCE_OBJECT), "\n\n";
// Outputs:
Associative array always output as object: {"foo":"bar","baz":"long"}
Associative array always output as object: {"foo":"bar","baz":"long"}The json_last_error_msg() function returns the error string of the last json_encode() or json_decode() call.
An updated version of the function might look like the code below.
<?php
if (!function_exists('json_last_error_msg')) {
function json_last_error_msg() {
static $ERRORS = array(
JSON_ERROR_NONE => 'No error',
JSON_ERROR_DEPTH => 'Maximum stack depth exceeded',
JSON_ERROR_STATE_MISMATCH => 'State mismatch (invalid or malformed JSON)',
JSON_ERROR_CTRL_CHAR => 'Control character error, possibly incorrectly encoded',
JSON_ERROR_SYNTAX => 'Syntax error',
JSON_ERROR_UTF8 => 'Malformed UTF-8 characters, possibly incorrectly encoded'
);
$error = json_last_error();
return isset($ERRORS[$error]) ? $ERRORS[$error] : 'Unknown error';
}
}Constants such as JSON_ERROR_NONE and JSON_ERROR_DEPTH are predefined by the JSON extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.
Similar to json_last_error_msg(), the json_last_error() function returns the last error that occurred during the last JSON encoding/decoding.
<?php
// A valid json string
$json[] = '{"Organization": "PHP Documentation Team"}';
// An invalid json string which will cause an syntax
// error, in this case we used ' instead of " for quotation
$json[] = "{'Organization': 'PHP Documentation Team'}";
foreach ($json as $string) {
echo 'Decoding: ' . $string;
json_decode($string);
switch (json_last_error()) {
case JSON_ERROR_NONE:
echo ' - No errors';
break;
case JSON_ERROR_DEPTH:
echo ' - Maximum stack depth exceeded';
break;
case JSON_ERROR_STATE_MISMATCH:
echo ' - Underflow or the modes mismatch';
break;
case JSON_ERROR_CTRL_CHAR:
echo ' - Unexpected control character found';
break;
case JSON_ERROR_SYNTAX:
echo ' - Syntax error, malformed JSON';
break;
case JSON_ERROR_UTF8:
echo ' - Malformed UTF-8 characters, possibly incorrectly encoded';
break;
default:
echo ' - Unknown error';
break;
}
echo PHP_EOL;
}
// Outputs:
Decoding: {"Organization": "PHP Documentation Team"} - No errors
Decoding: {'Organization': 'PHP Documentation Team'} - Syntax error, malformed JSONView the other sections:
Note: This article is based on PHP version 7.0.