PHP detect if it is a CONSTANT or a STRING before validating

Question

I am working on a function to validate variables and constants.

function checkVars($var){
 if(isConstant($var)){ <--here is my problem, how do I check if its a Constant and or a string?
  return defined($var);
 }else{
  //use other functions to check if its a valid variable
 }
}

Is there a way to check if its a string or a constant?

EDIT: The idea behind this is to save lines of code on recurring tasks like:

if(defined('CONS')){
 if(CONS > 0 && CONS !== false){
  //and so on..
 }
}

This is just an example but you could have 4 lines of code just to validate a constant or a variable to fit specific application needs.

The idea is to save all that work with a single function call that returns true or false:

if(isValid('CONS')){
 //do stuff on true
}else{
 //do stuff on false
}

I don't think you can check if a value is a constant. If a constant is passed in, it would be the value of the constant. Unless the value being passed in is the name of the constant itself. — aynber
– aynber, Commented Aug 27, 2020 at 13:33
Please provide an example of how you are calling this function, and what you expect it to return. — Alex Howansky
– Alex Howansky, Commented Aug 27, 2020 at 13:37
@aynber you can test to see if you have a constant with defined(name_of_constant) and you can check the value of the constant using constant(name_of_constant) — Jay Blanchard
– Jay Blanchard, Commented Aug 27, 2020 at 14:01

Jay Blanchard · Accepted Answer · 2020-08-27 14:29:20Z

2

You will use defined() to test to see if the constant exists and is defined. Then use is_string() with constant() to determine if the constant is a string. I assume you're using return because this condition is part of a function:

if(defined($constantName) and is_string(constant($constantName))) {
    return constant($constantName);
} else {
    // other code
}

Running the following test I could see that 'bar' was returned:

define("FOO", "bar");
$constantName = "FOO";

if(defined($constantName) and is_string(constant($constantName))) {
    echo constant($constantName); // 'bar'
} else {
    // other code
}

edited Aug 27, 2020 at 14:29

answered Aug 27, 2020 at 13:33

Jay Blanchard

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Comments

André Walker · Accepted Answer · 2020-08-27 16:14:38Z

2

check if a constant is defined by her name:

defined('CONSTANT');

check if any value is a string:

is_string(CONSTANT);

logically, if it's not a constant is just a string.

for check if is a constant you must pass the constant name in string. You also can check if exists a constant with the same value, using get_defined_constants(), but you will not know if is the same constant.

define('MYCONST', "THE VALUE");
function exists_a_constant($value)
{
    $constants = get_defined_constants(true);
    return in_array($value, $constants['user']); // true if finds or false if not
    // return array_search($value, $constants['user']);    //Will return the key (name of the constant)
}

function checkVars($var)
{
    if (exists_a_constant($var)) {
        echo "exists a constant";
    } else {
        echo "not";
    }
}

checkVars(MYCONST);
// exists a constant
checkVars('MYCONST');
// not
checkVars("THE VALUE");
// exists a constant
checkVars("random string");
// not

edited Aug 27, 2020 at 16:14

answered Aug 27, 2020 at 13:56

André Walker

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4 Comments

Crash Override Over a year ago

It returns TRUE even if the constant wasn't defined

André Walker Over a year ago

i forgot to use only the user defined constants. updated the answer @CrashOverride is working now.

Crash Override Over a year ago

Still not working but I changed array_search for array_key_exists and works perfectly. Added it as an answer, thanks for your help

André Walker Over a year ago

Strange. Works in here for checking a value. array_key_exists() will search the key. if you are receiving the key, you can check by defined('MYCONSTNAME').

Crash Override · Accepted Answer · 2020-08-27 15:51:04Z

-1

Based on André Walker answer I made a few changes and it works.

get_defined_constants gets an array with all the defined constants then I use array_key_exists to check if the constant you are passing is in the array.

define('FOO','bar');
function exists_a_constant($value){
    $constants = get_defined_constants();
    return array_key_exists($value,$constants); 
}

if(exists_a_constant('FOO')){
    echo 'defined';
}else{
    echo 'not defined';
}

thanks!

answered Aug 27, 2020 at 15:51

Crash Override

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1 Comment

IncredibleHat Over a year ago

I guess your question was misleading/confusing. This has nothing to do with checking if a variable is a string, but rather you are only checking if that constant was defined.

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