isset PHP isset($_GET['something']) ? $_GET['something'] : ''

问题

I am looking to expand on my PHP knowledge, and I came across something I am not sure what it is or how to even search for it. I am looking at php.net isset code, and I see isset($_GET['something']) ? $_GET['something'] : ''

I understand normal isset operations, such as if(isset($_GET['something']){ If something is exists, then it is set and we will do something } but I don't understand the ?, repeating the get again, the : or the ''. Can someone help break this down for me or at least point me in the right direction?

回答1:

It's commonly referred to as 'shorthand' or the Ternary Operator.

$test = isset($_GET['something']) ? $_GET['something'] : '';

means

if(isset($_GET['something'])) {
    $test = $_GET['something'];
} else {
    $test = '';
}

To break it down:

$test = ... // assign variable
isset(...) // test
? ... // if test is true, do ... (equivalent to if)
: ... // otherwise... (equivalent to else)

Or...

// test --v
if(isset(...)) { // if test is true, do ... (equivalent to ?)
    $test = // assign variable
} else { // otherwise... (equivalent to :)

回答2:

That's called a ternary operator and it's mainly used in place of an if-else statement.

In the example you gave it can be used to retrieve a value from an array given isset returns true

isset($_GET['something']) ? $_GET['something'] : ''

is equivalent to

if (isset($_GET['something'])) {
  $_GET['something'];
} else {
  '';
}

Of course it's not much use unless you assign it to something, and possibly even assign a default value for a user submitted value.

$username = isset($_GET['username']) ? $_GET['username'] : 'anonymous'

回答3:

From php 7 you can write it even shorter:

$age = $_GET['age']) ?? 27;

And this means if age param is provided in the url it will be set to $age var, or will default to 27

See all new features of php 7

回答4:

You have encountered the ternary operator. It's purpose is that of a basic if-else statement. The following pieces of code do the same thing.

Ternary:

$something = isset($_GET['something']) ? $_GET['something'] : "failed";

If-else:

if (isset($_GET['something'])) {
    $something = $_GET['something'];
} else {
    $something = "failed";
}

回答5:

It is called the ternary operator. It is shorthand for an if-else block. See here for an example http://www.php.net/manual/en/language.operators.comparison.php#language.operators.comparison.ternary

回答6:

? is called Ternary (conditional) operator : example

回答7:

What you're looking at is called a Ternary Operator, and you can find the PHP implementation here. It's an if else statement.

if (isset($_GET['something']) == true) {
    thing = isset($_GET['something']);
} else {
    thing = "";
}

回答8:

If you want an empty string default then a preferred way is one of these (depending on your need):

$str_value = strval($_GET['something']);
$trimmed_value = trim($_GET['something']);
$int_value = intval($_GET['somenumber']);

If the url parameter something doesn't exist in the url then $_GET['something'] will return null

strval($_GET['something']) -> strval(null) -> ""

and your variable $value is set to an empty string.

trim() might be prefered over strval() depending on code (e.g. a Name parameter might want to use it)
intval() if only numeric values are expected and the default is zero. intval(null) -> 0

Cases to consider:

...&something=value1&key2=value2 (typical)

...&key2=value2 (parameter missing from url $_GET will return null for it)

...&something=+++&key2=value (parameter is " ")

Why this is a preferred approach:

It fits neatly on one line and is clear what's going on.
It's readable than $value = isset($_GET['something']) ? $_GET['something'] : '';
Lower risk of copy/paste mistake or a typo: $value=isset($_GET['something'])?$_GET['somthing']:'';
It's compatible with older and newer php.

Update Strict mode may require something like this:

$str_value = strval(@$_GET['something']);
$trimmed_value = trim(@$_GET['something']);
$int_value = intval(@$_GET['somenumber']);

来源：https://stackoverflow.com/questions/12126420/isset-php-isset-getsomething-getsomething

标签

php

isset