自定义函数，用于检查是否设置了数组中的变量

Question

What I'm trying to do is write one function to reuse vs writing out an if statement every time.

If statement:

if (!isset($value)){ echo 'null';}else{ echo $value;}

Function:

function isSetTest($value){
    if ( !isset($value)){
       $value = NULL;
    }
    return $value;
}

echo'name'.isSetTest($value);

Function works but I still get the "undefined" error message which is what i'm trying to avoid.

Answer 1

Pass by reference instead, so that no processing of the variable is done until you want it:

function isSetTest(&$value) { // note the &
    if (!isset($value)) {
       $value = NULL;
    }
    return $value;
}

You can shorten this a bit:

function isSetTest(&$value) {
    return isset($value) ? $value : null;
}

I have a function that does something similar, except you can provide an optional default value in the case that the variable is not set:

function isset_or(&$value, $default = null) {
    return isset($value) ? $value : $default;
}

Answer 2

The problem in your code is, that you still pass an undefined variable to your function, so that's why you still get your undefined error.

One way to solve this now, is that you pass your variable name as a string and then use variable variables , to check if it exists, eg

function isSetTest($value){
    global $$value;
    if ( !isset($$value)){
       $$value = NULL;
    }
    return $$value;
}

echo'name'.isSetTest("value");

Demo