PHP 或空变量的简写

Question

$a = '';
$b = 1;

How to print $b if $a = '' using shorthand in PHP?

in javascript there is something like

a || b; 

Answer 1

Ternary Operator

$a = '';
$b = 1;

echo $a ?: $b; // 1

Until $a is evaluated false, $b will be displayed. Remember that the following things are considered to be empty :

"" (an empty string)
0 (0 as an integer)
0.0 (0 as a float)
"0" (0 as a string)
NULL
FALSE
array() (an empty array)
$var; (a variable declared, but without a value)

That means that if $a is "", 0, "0", null, false, array(), .. then $b will be displayed. See PHP type comparison tables .

If you want to display $b only when $a is an empty string, then you should uses strict comparison operators (===)

$a = '';
$b = 1;

echo $a === '' ? $b : ''; // 1

Answer 2

This is the shorthand for an IF/Else statement in PHP.

echo ($a != '' ? $a : $b)

If $a is not an empty string output (echo) $a otherwise output $b.

Answer 3

As others ahve said Turnary operator is handy for most senarios.

echo $a ?: $b;//b

But it is NOT shorthand for empty(). Ternary operator will issue notices if var/array keys/properties are not set.

echo $someArray['key that doesnt exist'] ?: $b;//Notice: Undefined index
echo $arrayThatDoesntExist['key-that-doesnt-exist'] ?: $b;//Notice: Undefined variable

empty() will take care of the additional checks for you and its recomended to just use it.

if (empty($arrayThatDoesntExist['key-that-doesnt-exist'])) echo $b;

You could technically just suppress the warning/notice with @ and the ternary operator becomes a replacement for empty().

@echo $someArray['key that doesnt exist'] ?: $b;
@echo $arrayThatDoesntExist['key-that-doesnt-exist'] ?: $b;

But usually not recommended as supressing notices and warnings could lead you into trouble later on plus I think it may have some performance impact.