PHP中empty()和isset()的區別介紹
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二者共同點
二者區別
1、對於未設置的變量的判斷
2、對於 "" (空字符串) 的判斷
3、對於 0 (作為整數的0) 的判斷
4、對於 0.0 (作為浮點數的0) 的判斷
5、對於 "0" (作為字符串的0) 的判斷
6、對於 NULL 的判斷
7、對於 FALSE 的判斷
8、對於 array() (一個空數組) 的判斷
二者共同點
都可以判定一個變量是否為空;
都返回boolean類型,即true或false。
二者區別
empty() 函數用於檢查一個變量是否為空。當一個變量並不存在,或者它的值等同於 FALSE,那麼它會被認為不存在。如果變量不存在的話,empty()並不會產生警告。
isset() 函數用於檢測變量是否已設置並且非 NULL。如果已經使用 unset() 釋放了一個變量之後,再通過 isset() 判斷將返回 FALSE。若使用 isset() 測試一個被設置成 NULL 的變量,將返回 FALSE。同時要注意的是 null 字符("")並不等同於 PHP 的 NULL 常量。
對於 0、false、空字符串、空數組的判斷上,empty() 可以識別為空,isset() 則不能識別。
1、對於未設置的變量的判斷
// 對於未設置的變量的判斷if (empty($a)) { echo "empty:變量為空" . "<br>";} else { echo "empty:變量不為空" . "<br>";}if (isset($a)) { echo "isset:變量已設置且不為空" . "<br>";} else { echo "isset:變量未設置或變量為空" . "<br>";}##結果empty:變量為空isset:變量未設置或變量為空
2、對於 "" (空字符串) 的判斷
// 對於 "" (空字符串) 的判斷$a = "";if (empty($a)) { echo "empty:變量為空" . "<br>";} else { echo "empty:變量不為空" . "<br>";}if (isset($a)) { echo "isset:變量已設置且不為空" . "<br>";} else { echo "isset:變量未設置或變量為空" . "<br>";}##結果empty:變量為空isset:變量已設置且不為空
3、對於 0 (作為整數的0) 的判斷
// 對於 0 (作為整數的0) 的判斷$a = 0;if (empty($a)) { echo "empty:變量為空" . "<br>";} else { echo "empty:變量不為空" . "<br>";}if (isset($a)) { echo "isset:變量已設置且不為空" . "<br>";} else { echo "isset:變量未設置或變量為空" . "<br>";}##結果empty:變量為空isset:變量已設置且不為空
4、對於 0.0 (作為浮點數的0) 的判斷
// 對於 0.0 (作為浮點數的0) 的判斷$a = 0.0;if (empty($a)) { echo "empty:變量為空" . "<br>";} else { echo "empty:變量不為空" . "<br>";}if (isset($a)) { echo "isset:變量已設置且不為空" . "<br>";} else { echo "isset:變量未設置或變量為空" . "<br>";}##結果empty:變量為空isset:變量已設置且不為空
5、對於 "0" (作為字符串的0) 的判斷
// 對於 "0" (作為字符串的0) 的判斷$a = "0";if (empty($a)) { echo "empty:變量為空" . "<br>";} else { echo "empty:變量不為空" . "<br>";}if (isset($a)) { echo "isset:變量已設置且不為空" . "<br>";} else { echo "isset:變量未設置或變量為空" . "<br>";}##結果empty:變量為空isset:變量已設置且不為空
6、對於 NULL 的判斷
// 對於 NULL 的判斷$a = null;if (empty($a)) { echo "empty:變量為空" . "<br>";} else { echo "empty:變量不為空" . "<br>";}if (isset($a)) { echo "isset:變量已設置且不為空" . "<br>";} else { echo "isset:變量未設置或變量為空" . "<br>";}##結果empty:變量為空isset:變量未設置或變量為空
7、對於 FALSE 的判斷
// 對於 FALSE 的判斷$a = false;if (empty($a)) { echo "empty:變量為空" . "<br>";} else { echo "empty:變量不為空" . "<br>";}if (isset($a)) { echo "isset:變量已設置且不為空" . "<br>";} else { echo "isset:變量未設置或變量為空" . "<br>";}##結果empty:變量為空isset:變量已設置且不為空
8、對於 array() (一個空數組) 的判斷
// 對於 array() (一個空數組) 的判斷$a = array();if (empty($a)) { echo "empty:變量為空" . "<br>";} else { echo "empty:變量不為空" . "<br>";}if (isset($a)) { echo "isset:變量已設置且不為空" . "<br>";} else { echo "isset:變量未設置或變量為空" . "<br>";}##結果empty:變量為空isset:變量已設置且不為空
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