(PHP 4, PHP 5, PHP 7)
isset — 锟斤拷锟斤拷锟斤拷锟角凤拷锟斤拷锟斤拷锟矫诧拷锟揭凤拷 NULL
锟斤拷锟斤拷锟斤拷锟角凤拷锟斤拷锟矫ｏ拷锟斤拷锟揭诧拷锟斤拷 NULL锟斤拷
锟斤拷锟斤拷丫锟绞癸拷锟� unset()
锟酵凤拷锟斤拷一锟斤拷锟斤拷锟斤拷之锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷
isset()锟斤拷锟斤拷使锟斤拷 isset()
锟斤拷锟斤拷一锟斤拷锟斤拷锟斤拷锟矫筹拷 NULL 锟侥憋拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷 FALSE锟斤拷同时要注锟斤拷锟斤拷锟� null 锟街凤拷锟斤拷"\0"锟斤拷锟斤拷锟斤拷锟斤拷同锟斤拷
PHP 锟斤拷 NULL 锟斤拷锟斤拷锟斤拷
锟斤拷锟揭伙拷未锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟矫�
isset() 只锟斤拷锟斤拷全锟斤拷锟斤拷锟斤拷锟斤拷锟皆憋拷锟斤拷锟斤拷时锟斤拷锟斤拷 TRUE 锟斤拷锟斤拷锟斤拷檀锟斤拷锟斤拷锟斤拷遥锟斤拷锟酵撅拷锟斤拷锟矫伙拷锟斤拷锟斤拷玫谋锟斤拷锟绞憋拷突锟斤拷锟斤拷锟酵Ｖ癸拷锟�
var要锟斤拷锟侥憋拷锟斤拷锟斤拷
...锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷
锟斤拷锟� var 锟斤拷锟节诧拷锟斤拷值锟斤拷锟斤拷 NULL 锟津返伙拷 TRUE锟斤拷锟斤拷锟津返伙拷 FALSE锟斤拷
| 锟芥本 | 说锟斤拷 |
|---|---|
| 5.4.0 |
锟斤拷锟斤拷址锟斤拷姆锟斤拷锟斤拷锟狡拷锟斤拷锟斤拷锟斤拷岱碉拷锟� |
Example #1 isset() 锟斤拷锟斤拷
<?php
$var = '';
// 锟斤拷锟轿� TRUE锟斤拷锟斤拷锟皆猴拷叩锟斤拷谋锟斤拷锟斤拷锟斤拷锟接★拷锟斤拷锟斤拷锟�
if (isset($var)) {
echo "This var is set so I will print.";
}
// 锟节猴拷叩锟斤拷锟斤拷锟斤拷校锟斤拷锟斤拷墙锟绞癸拷锟� var_dump 锟斤拷锟� isset() 锟侥凤拷锟斤拷值锟斤拷
// the return value of isset().
$a = "test";
$b = "anothertest";
var_dump(isset($a)); // TRUE
var_dump(isset($a, $b)); // TRUE
unset ($a);
var_dump(isset($a)); // FALSE
var_dump(isset($a, $b)); // FALSE
$foo = NULL;
var_dump(isset($foo)); // FALSE
?>
锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷械锟皆拷锟揭餐拷锟斤拷锟叫э拷锟�
<?php
$a = array ('test' => 1, 'hello' => NULL, 'pie' => array('a' => 'apple'));
var_dump(isset($a['test'])); // TRUE
var_dump(isset($a['foo'])); // FALSE
var_dump(isset($a['hello'])); // FALSE
// 锟斤拷 'hello' 锟斤拷值锟斤拷锟斤拷 NULL锟斤拷锟斤拷锟皆憋拷锟斤拷为锟斤拷未锟斤拷值锟侥★拷
// 锟斤拷锟斤拷锟斤拷锟� NULL 锟斤拷值锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟铰边的凤拷锟斤拷锟斤拷
var_dump(array_key_exists('hello', $a)); // TRUE
// Checking deeper array values
var_dump(isset($a['pie']['a'])); // TRUE
var_dump(isset($a['pie']['b'])); // FALSE
var_dump(isset($a['cake']['a']['b'])); // FALSE
?>
Example #2 锟斤拷锟街凤拷锟斤拷位锟斤拷锟斤拷使锟斤拷 isset()
PHP 5.4 锟侥憋拷锟剿达拷锟斤拷锟街凤拷锟斤拷位锟斤拷时 isset() 锟斤拷锟斤拷为锟斤拷
<?php
$expected_array_got_string = 'somestring';
var_dump(isset($expected_array_got_string['some_key']));
var_dump(isset($expected_array_got_string[0]));
var_dump(isset($expected_array_got_string['0']));
var_dump(isset($expected_array_got_string[0.5]));
var_dump(isset($expected_array_got_string['0.5']));
var_dump(isset($expected_array_got_string['0 Mostel']));
?>
锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷PHP 5.3锟叫碉拷锟斤拷锟斤拷锟�
bool(true) bool(true) bool(true) bool(true) bool(true) bool(true)
锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷PHP 5.4锟叫碉拷锟斤拷锟斤拷锟�
bool(false) bool(true) bool(true) bool(true) bool(false) bool(false)
isset() 只锟斤拷锟斤拷锟节憋拷锟斤拷锟斤拷锟斤拷为锟斤拷锟斤拷锟轿猴拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷山锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟�锟斤拷锟斤拷锟角凤拷锟斤拷锟斤拷锟矫ｏ拷锟斤拷使锟斤拷 defined() 锟斤拷锟斤拷锟斤拷
Note: 锟斤拷为锟斤拷一锟斤拷锟斤拷锟皆癸拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷一锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟杰憋拷 锟缴变函锟斤拷 锟斤拷锟矫★拷
Note:
锟斤拷锟绞癸拷锟� isset() 锟斤拷锟斤拷锟斤拷锟斤拷锟睫凤拷锟斤拷锟绞碉拷锟斤拷锟皆ｏ拷锟斤拷锟� __isset() 锟斤拷锟斤拷锟窖撅拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷胤锟斤拷锟斤拷锟�