Question

I dont understand the function, call_user_func() in the sense that i get how it works but I’m not sure why its required or in what context to use it in php. As far as I’m concerned why not just call the function instead of calling a function with a function? Thnx!

Answer 1

I’ve had a couple situations where this was very necessary. For example, when I was creating a project that allowed a user to construct parts of a programming language, the system would wrap the “tag” definition in a function before running it for security reasons. However, in doing this, I can’t simply call those functions, because I don’t know when I need to call them, or even what the names would be. Enter call_user_func()…

So, I’m sure you’re confused right now. Let me explain. What my system did, was take some XML, and convert it into PHP/HTML/JS with PHP. This allowed for rapid creation of GUIs (which was the goal). Take this XML for example:

<window id="login-win" title="Access Restricted" width="310" height="186" layout="accordion" layoutConfig="animate:true">
    <panel id="login-panel" title="User Login">
        <form id="login-form" title="Credentials">
            <textbox id="login-uname" label="Username"/>
            <password id="login-pass" label="Password"/>
            <submit text="Login"/>
        </form>
    </panel>
    <panel id="login-register" title="Register">
        Nothing, you can't register!
    </panel>
</window>

Each XML tag would be read, then fed into it’s corresponding PHP function. That function would determine what to do for that 1 tag. In order to pull this off, I had files each named after the tag it handled. So, for example, the tag’s file was “submit.php”. This file’s contents would get wrapped in a generated function, something like:

function tag_submit($variables, $parent, $children){

    // deal with the data, then echo what is needed

}

This function’s name would be stored in an array, with it’s associated tag name, with the rest of the generated functions. This makes it so the function is generated once, and only created when needed, saving memory, since I would do a if(func_exists()) call to determine if I needed it or not.

However, since this is all dynamic, and the user may want to add in a new tag, for say, a < date > tag, I needed to use call_user_func() to get things to work. I can’t hard-code a function call if I don’t know what the name is.

Hope that all made sense. Basically, yes, it is a rarely used function, but it is still very very useful.