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Booleans in PHP

By: Andi, Stig and Derick in PHP Tutorials on 2008年11月22日 [フレーム]

Booleans were introduced for the first time in PHP 4 and didn"t exist in prior versions. A Boolean value can be either true or false. PHP automatically converts types when needed. Boolean is probably the type that other types are most often converted to behind the scenes. This is because, in any conditional code such as if statements, loops, and so on, types are converted to this scalar type to check if the condition is satisfied. Also, comparison operators result in a Boolean value.

Consider the following code fragment:

$numerator = 1;

$denominator = 5;

if ($denominator == 0) {

print "The denominator needs to be a non-zero number\n";

}

The result of the equal-than operator is a Boolean; in this case, it would be false and, therefore, the if() statement would not be entered. Now, consider the next code fragment:

$numerator = 1;

$denominator = 5;

if ($denominator) {

/* Perform calculation */

} else {

print "The denominator needs to be a non-zero number\n";

}

You can see that no comparison operator was used in this example; however, PHP automatically internally converted $denominator or, to be more accurate, the value 5 to its Boolean equivalent, true, to perform the if() statement and, therefore, enter the calculation. Although not all types have been covered yet, the following table shows truth values for their values.

Data Type False Values True Values

Integer 0 All non-zero values

Floating point 0.0 All non-zero values

Strings
Empty strings ()""
The zero string ()"0" All other strings

Null Always Never

Array
If it does not contain any elements
If it contains at least one element

Object Never Always

Resource Never Always

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