Php unset null memory

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But there is something unique on this comparative when I am not using unset or NULL, xdebug give me as memory usage. So, I think giving line to use unset or NULL will add process to your application and it will be better to stay origin with your code and decrease the variable that you are using as effective as you can.

Conclusion, both null and unset free memory as expected not only at the end of the execution. Also, reassigning a variable holds the value twice at some point versus Code example from comment. But i can only test it on an PHP 5. How important is it to unset variables in PHP? Notes Note : Because this is a language construct and not a function, it cannot be called using variable functions. This is probably trivial but there is no error for unsetting a non-existing variable.

You don't need to check that a variable is set before you unset it. The former case is just plain bad design. Since unset is a language construct, it cannot be passed anything other than a variable.

It's sole purpose is to "unset" this variable, ie. This is true especially for reference variables, where not the actual value is destroyed but the reference to that value.

This is why you can't wrap 'unset ' in a user defined function: You would either unset a copy of the data if the parameter is passed by value, or you would just unset the reference variable within the functions scope if the parameter is passed by reference. There is no workaround for that, as you cannot pass 'scope' to a function in PHP.

I don't know how PHP handles garbage collection internally, but I guess this behavior can result in a huge memory leak: if a value variable goes out of scope with a second variable still holding a reference to the in-memory value, then unsetting that reference would still hold the value in memory but potentially unset the last reference to that in-memory data, hence: occupied memory that is rendered useless as you cannot reference it anymore.

A sample how to unset array elements from an array result coming from a mysql request. In this sample it is checking if a file exists and removes the row from the array if it not exists.

To clarify what hugo dot dworak at gmail dot com said about unsetting things that aren't already set: unsetting a non-existent key within an array does NOT throw an error. Adding on to what bond at noellebond dot com said, if you want to remove an index from the end of the array, if you use unset, the next index value will still be what it would have been.

The only time where this would not seem right is when you remove a value off the end. Recommended Articles. Article Contributed By :. Easy Normal Medium Hard Expert. Writing code in comment? Please use ide.

Load Comments. What's New. Most popular in PHP. It is no more a function call than a return or an include. Aside from performance issues, using unset makes your code's intent much clearer. By doing an unset on a variable, you've essentially marked the variable for 'garbage collection' PHP doesn't really have one, but for example's sake so the memory isn't immediately available. The variable no longer houses the data, but the stack remains at the larger size.

Doing the null method drops the data and shrinks the stack memory almost immediately. This has been from personal experience and others as well. See the comments of the unset function here. I personally use unset between iterations in a loop so that I don't have to have the delay of the stack being yo-yo'd in size. The data is gone, but the footprint remains. On the next iteration, the memory is already being taken by php and thus, quicker to initialize the next variable.

Keep in mind microtime true doesn't work in PHP 4. Regarding objects, especially in lazy-load scenario, one should consider garbage collector is running in idle CPU cycles, so presuming you're going into trouble when a lot of objects are loading small time penalty will solve the memory freeing.

Tested on production server, originally the job consumed 50MB and then was halted. After nanosleep was used 14MB was constant memory consumption. But it works on PHP 5. I still doubt about this, but I've tried it at my script and I'm using xdebug to know how it will affect my app memory usage.

The script is set on my function like this :. But there is something unique on this comparative when I am not using unset or NULL, xdebug give me as memory usage. So, I think giving line to use unset or NULL will add process to your application and it will be better to stay origin with your code and decrease the variable that you are using as effective as you can. Conclusion, both null and unset free memory as expected not only at the end of the execution. Also, reassigning a variable holds the value twice at some point versus Code example from comment.

I used arrays, as you see it didn't matter now. But i can only test it on an PHP 5. How important is it to unset variables in PHP? Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow.