Cannot use string offset as an array in php

I was able to reproduce this once I upgraded to PHP 7. It breaks when you try to force array elements into a string.

$params = '';
foreach ($foo) {
  $index = 0;
  $params[$index]['keyName'] = $name . '.' . $fileExt;
}

After changing:

$params = '';

to:

$params = array();

I stopped getting the error. I found the solution in this bug report thread. I hope this helps.

I was fighting a similar problem, so documenting here in case useful.

In a __get() method I was using the given argument as a property, as in (simplified example):

function __get($prop) {
     return $this->$prop;
}

...i.e. $obj->fred would access the private/protected fred property of the class.

I found that when I needed to reference an array structure within this property it generated the Cannot use String offset as array error. Here's what I did wrong and how to correct it:

function __get($prop) {
     // this is wrong, generates the error
     return $this->$prop['some key'][0];
}

function __get($prop) {
     // this is correct
     $ref = & $this->$prop;
     return $ref['some key'][0];
}

Explanation: in the wrong example, php is interpreting ['some key'] as a key to $prop (a string), whereas we need it to dereference $prop in place. In Perl you could do this by specifying with {} but I don't think this is possible in PHP.

I had this error for the first time ever while trying to debug some old legacy code, running now on PHP 7.30. The simplified code looked like this:

$testOK = true;

if ($testOK) {
    $x['error'][] = 0;
    $x['size'][] = 10;
    $x['type'][] = 'file';
    $x['tmp_name'][] = 'path/to/file/';
}

The simplest fix possible was to declare $x as array() before:

$x = array();

if ($testOK) {
    // same code
}

I was having this error and a was nuts

my code was

$aux_users='';

foreach ($usuarios['a'] as $iterador) { 
#code
if ( is_numeric($consultores[0]->ganancia) ) {
    $aux_users[$iterador]['ganancia']=round($consultores[0]->ganancia,2);
  }
}

after changing $aux_users=''; to $aux_users=array();

it happen to my in php 7.2 (in production server!) but was working on php 5.6 and php 7.0.30 so be aware! and thanks to Young Michael, i hope it helps you too!

Since the release PHP 7.1+, is not more possible to assign a value for an array as follow:

$foo = ""; 
$foo['key'] = $foo2; 

because as of PHP 7.1.0, applying the empty index operator on a string throws a fatal error. Formerly, the string was silently converted to an array.