Question

When I use file_get_contents and pass it as a parameter to another function, without assigning it to a variable, does that memory get released before the script execution finishes?

For Example:

preg_match($pattern, file_get_contents('http://domain.tld/path/to/file.ext'), $matches); 

Will the memory used by file_get_contents be released before the script finishes?

Answer 1

The temporary string created to hold the file contents will be destroyed. Without delving into the sources to confirm, here’s a couple of ways you can test that a temporary value created as a function parameter gets destroyed:

Method 1: a class which reports its destruction

This demonstrates lifetime by using a class which reports on its own demise:

class lifetime {     public function __construct()     {          echo 'construct\n';     }     public function __destruct()     {          echo 'destruct\n';     }   }  function getTestObject() {    return new lifetime(); }   function foo($obj) {    echo 'inside foo\n'; }     echo 'Calling foo\n'; foo(getTestObject()); echo 'foo complete\n'; 

This outputs

Calling foo construct inside foo destruct foo complete 

Which indicates that the implied temporary variable is destroyed right after the foo function call.

Method 2: measure memory usage

Here’s another method which offers further confirmation using memory_get_usage to measure how much we’ve consumed.

function foo($str) {    $length=strlen($str);     echo 'in foo: data is $length, memory usage='.memory_get_usage().'\n'; }  echo 'start: '.memory_get_usage().'\n'; foo(file_get_contents('/tmp/three_megabyte_file')); echo 'end: '.memory_get_usage().'\n'; 

This outputs

start: 50672 in foo: data is 2999384, memory usage=3050884 end: 51544