Passing and using an array by reference in PHP [closed]

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In a PHP function, I'd like to append values to an array that was passed in by reference. For example:

function foo(array &$arr) {
    $arr[] = "error on this line";
    $arr[] = "more";
    $arr[] = "stuff";
}

The error I get when I attempt to append something to the array is

PHP Parse error:  syntax error, unexpected ']', expecting T_STRING or T_VARIABLE or T_NUM_STRING in somefile.class.php on line xxx

I'm not sure I have the parameter defined correctly, or if this is even possible. Googling has so far not turned up any comparable examples.

EDIT: PHP Version 5.1.6.

Your example function works just fine. Please expand your example code to a reproducible error. — Decent Dabbler
– Decent Dabbler, Commented Aug 4, 2015 at 20:46
I can't reproduce the error with 5.1.6, sandbox.onlinephpfunctions.com/code/…. — chris85
– chris85, Commented Aug 4, 2015 at 20:57
Looks like an error a dozen lines before it caused the parsing error. But I'm happy to know about array_push(). — Marvo
– Marvo, Commented Aug 4, 2015 at 21:08

rtheunissen · Accepted Answer · 2015-08-04 20:48:21Z

2

I just ran your code and got the expected output, so I'm not sure what's happening. If arr wasn't an array, it wouldn't pass the typehint, so it's definitely an array.

It's possible that you're running PHP < 5.4

<?php

function foo(array &$arr) {
    $arr[] = "error on this line";
    $arr[] = "more";
    $arr[] = "stuff";
}

$a = ["initial"];

foo($a);

var_dump($a);

/*
array(4) {
  [0] =>
  string(7) "initial"
  [1] =>
  string(18) "error on this line"
  [2] =>
  string(4) "more"
  [3] =>
  string(5) "stuff"
}
*/

For PHP < 5.4:

<?php

function foo(array &$arr) {
    array_push($arr, "error on this line");
    array_push($arr, "more");
    array_push($arr, "stuff");
}

$a = array("initial");

foo($a);

var_dump($a);

/*
array(4) {
  [0] =>
  string(7) "initial"
  [1] =>
  string(18) "error on this line"
  [2] =>
  string(4) "more"
  [3] =>
  string(5) "stuff"
}
*/

edited Aug 4, 2015 at 20:48

answered Aug 4, 2015 at 20:43

rtheunissen

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4 Comments

Korikulum Over a year ago

You can't use short array syntax in PHP < 5.4.

rtheunissen Over a year ago

That was the entire point I was trying to make. Just forgot to change the initialisation part as well (edited).

Korikulum Over a year ago

Also, you don't need array_push since $arr[] = is valid PHP 5.3 syntax.

Marvo Over a year ago

Turns out I'm on 5.1.6.

fsalazar_sch · Accepted Answer · 2015-08-04 20:41:02Z

1

You can use array_push

//The argument '$arr' is declared to be passed by reference, 
 array_push($arr, &$r);

You can check details here: http://php.net/manual/en/language.references.pass.php

answered Aug 4, 2015 at 20:41

fsalazar_sch

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Comments

luklapp · Accepted Answer · 2015-08-04 20:40:38Z

0

You don't need the "array" keyword before the parameter. The following code works for me:

$arr = array();

function foo(&$arr) {
    $arr[] = "error on this line";
    $arr[] = "more";
    $arr[] = "stuff";
}

foo($arr);

print_r($arr);

Output:

Array ( [0] => error on this line [1] => more [2] => stuff )

EDIT: PHP-version is 5.6

answered Aug 4, 2015 at 20:40

luklapp

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1 Comment

ToolmakerSteve Over a year ago

FWIW: While its true that you don't need to use type hints in php, that is not relevant to the error in the question. (I'm sure it also worked on your php with the word "array", so this doesn't tell us anything about why it isn't working for the person asking the question.)

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