Essential Books

Using constants

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To use the constant simply use its name: 

if (EARTH_IS_FLAT) {
    print "Earth is flat";
}

print APP_ENV_UPPERCASE;

or if you don’t know the name of the constant in advance, use the constant function: 

// this code is equivalent to the above code
$const1 = "EARTH_IS_FLAT";
$const2 = "APP_ENV_UPPERCASE";

if (constant($const1)) {
    print "Earth is flat";
}

print constant($const2);
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Constants:
* Constants
* Defining constants
* Class Constants
* Checking if constant is defined
* Constant arrays
* Using constants
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