Hướng dẫn is_resource in php

[PHP 4, PHP 5, PHP 7, PHP 8]

is_resource — Finds whether a variable is a resource

Description

is_resource[mixed $value]: bool

Parameters

The variable being evaluated.

Return Values

Returns true if value is a resource, false otherwise.

Examples

Example #1 is_resource[] example

The above example will output:

Notes

Note:

is_resource[] is not a strict type-checking method: it will return false if value is a resource variable that has been closed.

btleffler [AT] gmail [DOT] com ¶

11 years ago

I was recently trying to loop through some objects and convert them to arrays so that I could encode them to json strings.

I was running into issues when an element of one of my objects was a SoapClient. As it turns out, json_encode[] doesn't like any resources to be passed to it. My simple fix was to use is_resource[] to determine whether or not the variable I was looking at was a resource.

I quickly realized that is_resource[] returns false for two out of the 3 resources that are typically in a SoapClient object. If the resource type is 'Unknown' according to var_dump[] and get_resource_type[], is_resource[] doesn't think that the variable is a resource!

My work around for this was to use get_resource_type[] instead of is_resource[], but that function throws an error if the variable you're checking isn't a resource.

So how are you supposed to know when a variable is a resource if is_resource[] is unreliable, and get_resource_type[] gives errors if you don't pass it a resource?

I ended up doing something like this:



The @ operator suppresses the errors thrown by get_resource_type[] so it returns null if $possibleResource isn't a resource.

I spent way too long trying to figure this stuff out, so I hope this comment helps someone out if they run into the same problem I did.

CertaiN ¶

8 years ago

Try this to know behavior:



It will be shown as...

[Check Valid Resource]
[bool]$resource => TRUE
get_resource_type[$resource] => stream
is_resource[$resource] => TRUE

[Check Released Resource]
[bool]$resource => TRUE
get_resource_type[$resource] => Unknown
is_resource[$resource] => FALSE

[Check NULL]
[bool]$resource => FALSE
get_resource_type[$resource] => FALSE
Warning:  get_resource_type[] expects parameter 1 to be resource, null given in ... on line 10
is_resource[$resource] => FALSE

Anonymous ¶

4 years ago

Note that is_resource[] is unreliable. It considers closed resources as false:



That's the reason why some other people here have been confused and devised some complex [bad] "solutions" to detect resources...

There's a much better solution... In fact, I just showed it above, but here it is again with a more complete example:



So how do you check if something is a resource?

Like this!



How it works:

- An active resource is a resource, so check that first for efficiency.
- Then branch to check what the variable is NOT:
- A resource is never NULL. [We do that check via `!== null` for efficiency].
- A resource is never Scalar [int, float, string, bool].
- A resource is never an array.
- A resource is never an object.
- Only one variable type remains if all of the above checks succeeded: IF it's NOT any of the above, then it's a closed resource!

Just surfed by and saw the bad and hacky methods other people had left, and wanted to help out with this proper technique. Good luck, everyone!

PS: The core problem is that is_resource[] does a "loose" check for "living resource". I wish that it had a $strict parameter for "any resource" instead of these user-workarounds being necessary.