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{"id":148,"date":"2011-09-30T04:18:04","date_gmt":"2011-09-30T04:18:04","guid":{"rendered":"http:\/\/www.01xj.net\/0\/?p=148"},"modified":"2011-09-30T04:18:04","modified_gmt":"2011-09-30T04:18:04","slug":"php%e4%b8%ad%e7%9a%84isset%ef%bc%88%ef%bc%89%e5%87%bd%e6%95%b0%e7%9a%84%e7%94%a8%e6%b3%95","status":"publish","type":"post","link":"https:\/\/www.01xj.net\/?p=148","title":{"rendered":"php\u4e2d\u7684isset\uff08\uff09\u51fd\u6570\u7684\u7528\u6cd5"},"content":{"rendered":"

isset<\/h1>\n
\n

(PHP 3, PHP 4, PHP 5 )<\/p>\n

isset — \u68c0\u6d4b\u53d8\u91cf\u662f\u5426\u8bbe\u7f6e<\/p><\/div>\n

 <\/p>\n

\u63cf\u8ff0<\/h1>\n
bool\u00a0isset<\/strong>\u00a0( mixed var [, mixed var [, …]])<\/div>\n

\u5982\u679c\u00a0var<\/var>\u00a0\u5b58\u5728\u5219\u8fd4\u56de\u00a0TRUE<\/span><\/strong><\/tt>\uff0c\u5426\u5219\u8fd4\u56de\u00a0FALSE<\/span><\/strong><\/tt>\u3002<\/p>\n

\u5982\u679c\u5df2\u7ecf\u4f7f\u7528\u00a0unset()<\/strong>\u00a0\u91ca\u653e\u4e86\u4e00\u4e2a\u53d8\u91cf\u4e4b\u540e\uff0c\u5b83\u5c06\u4e0d\u518d\u662f\u00a0isset()<\/strong>\u3002\u82e5\u4f7f\u7528\u00a0isset()<\/strong>\u00a0\u6d4b\u8bd5\u4e00\u4e2a\u88ab\u8bbe\u7f6e\u6210\u00a0NULL<\/span><\/strong><\/tt>\u7684\u53d8\u91cf\uff0c\u5c06\u8fd4\u56de\u00a0FALSE<\/span><\/strong><\/tt>\u3002\u540c\u65f6\u8981\u6ce8\u610f\u7684\u662f\u4e00\u4e2a\u00a0NULL<\/span><\/strong><\/tt>\u00a0\u5b57\u8282\uff08“\\0”<\/var>\uff09\u5e76\u4e0d\u7b49\u540c\u4e8e PHP \u7684\u00a0NULL<\/span><\/strong><\/tt>\u00a0\u5e38\u6570\u3002<\/p>\n

\u8b66\u544a:\u00a0<\/strong>isset()<\/strong>\u00a0\u53ea\u80fd\u7528\u4e8e\u53d8\u91cf\uff0c\u56e0\u4e3a\u4f20\u9012\u4efb\u4f55\u5176\u5b83\u53c2\u6570\u90fd\u5c06\u9020\u6210\u89e3\u6790\u9519\u8bef\u3002\u82e5\u60f3\u68c0\u6d4b\u5e38\u91cf\u662f\u5426\u5df2\u8bbe\u7f6e\uff0c\u53ef\u4f7f\u7528defined()<\/strong>\u00a0\u51fd\u6570\u3002<\/p>\n

 <\/p>\n\n\n\n
<?php<\/p>\n

$var\u00a0<\/span>=\u00a0<\/span>”<\/span><\/span>;<\/p>\n

<\/span>\/\/ \u7ed3\u679c\u4e3a TRUE\uff0c\u6240\u4ee5\u540e\u8fb9\u7684\u6587\u672c\u5c06\u88ab\u6253\u5370<\/span>\u51fa\u6765\u3002
\n<\/span><\/span>if (isset(<\/span>$var<\/span><\/span>)) {
\nprint\u00a0<\/span>“This var is set set so I will print.”<\/span><\/span>;
\n}<\/p>\n

<\/span>\/\/ \u5728\u540e\u8fb9\u7684\u4f8b\u5b50\u4e2d\uff0c\u6211\u4eec\u5c06\u4f7f\u7528 var_dump \u8f93\u51fa isset() \u7684\u8fd4\u56de\u503c\u3002<\/p>\n

<\/span>$a\u00a0<\/span>=\u00a0<\/span>“test”<\/span><\/span>;
\n<\/span>$b\u00a0<\/span>=\u00a0<\/span>“anothertest”<\/span><\/span>;<\/p>\n

<\/span>var_dump<\/span>( isset(<\/span>$a<\/span>) );\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span><\/span>\/\/ TRUE
\n<\/span>var_dump<\/span>( isset (<\/span>$a<\/span>,\u00a0<\/span>$b<\/span>) );\u00a0<\/span><\/span>\/\/ TRUE<\/p>\n

<\/span>unset (<\/span>$a<\/span><\/span>);<\/p>\n

<\/span>var_dump<\/span>( isset (<\/span>$a<\/span>) );\u00a0\u00a0\u00a0\u00a0\u00a0<\/span><\/span>\/\/ FALSE
\n<\/span>var_dump<\/span>( isset (<\/span>$a<\/span>,\u00a0<\/span>$b<\/span>) );\u00a0<\/span><\/span>\/\/ FALSE<\/p>\n

<\/span>$foo\u00a0<\/span>=\u00a0<\/span>NULL<\/span><\/span>;
\n<\/span>var_dump<\/span>( isset (<\/span>$foo<\/span>) );\u00a0\u00a0\u00a0<\/span><\/span>\/\/ FALSE<\/p>\n

<\/span>?><\/span><\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u8fd9\u5bf9\u4e8e\u6570\u7ec4\u4e2d\u7684\u5143\u7d20\u4e5f\u540c\u6837\u6709\u6548\uff1a<\/p>\n

 <\/p>\n\n\n\n
<?php<\/p>\n

$a\u00a0<\/span>= array (<\/span>‘test’\u00a0<\/span>=>\u00a0<\/span>1<\/span>,\u00a0<\/span>‘hello’\u00a0<\/span>=>\u00a0<\/span>NULL<\/span><\/span>);<\/p>\n

<\/span>var_dump<\/span>( isset (<\/span>$a<\/span>[<\/span>‘test’<\/span>]) );\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span><\/span>\/\/ TRUE
\n<\/span>var_dump<\/span>( isset (<\/span>$a<\/span>[<\/span>‘foo’<\/span>]) );\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span><\/span>\/\/ FALSE
\n<\/span>var_dump<\/span>( isset (<\/span>$a<\/span>[<\/span>‘hello’<\/span>]) );\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span><\/span>\/\/ FALSE<\/p>\n

\/\/ \u952e ‘hello’ \u7684\u503c\u7b49\u4e8e NULL\uff0c\u6240\u4ee5\u88ab\u8ba4\u4e3a\u662f\u672a\u7f6e\u503c\u7684\u3002
\n\/\/ \u5982\u679c\u60f3\u68c0\u6d4b NULL \u952e\u503c\uff0c\u53ef\u4ee5\u8bd5\u8bd5\u4e0b\u8fb9\u7684\u65b9\u6cd5\u3002
\n<\/span>var_dump<\/span>(\u00a0<\/span>array_key_exists<\/span>(<\/span>‘hello’<\/span>,\u00a0<\/span>$a<\/span>) );\u00a0<\/span><\/span>\/\/ TRUE<\/p>\n

<\/span>?><\/span><\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u6ce8:\u00a0<\/strong>\u7531\u4e8e\u8fd9\u662f\u4e00\u4e2a\u8bed\u8a00\u7ed3\u6784\u800c\u975e\u51fd\u6570\uff0c\u56e0\u6b64\u5b83\u65e0\u6cd5\u88ab\u201c\u53d8\u91cf\u51fd\u6570\u201d\u8c03\u7528\u3002<\/p>\n

\n
    \u5408\u7406\u5e94\u7528PHP\u51fd\u6570isset()\u53ef\u4ee5\u5e2e\u52a9\u6211\u4eec\u662f\u68c0\u6d4b\u53d8\u91cf\u662f\u5426\u8bbe\u7f6e\u3002\u82e5\u679c\u53d8\u91cf\u4e0d\u5b58\u5728\u5219\u8fd4\u56de FALSE\uff0c\u800c\u5982\u679c\u53d8\u91cf\u5b58\u5728\u4e14\u503c\u4e0d\u4e3aNULL\uff0c\u5219\u8fd4\u56de TURE\u3002<\/ul>\n<\/div>\n

     <\/p>\n

    \u901a\u8fc7\u5bf9PHP\u8bed\u8a00\u7684\u5b66\u4e60\uff0c\u5e94\u8be5\u77e5\u9053\u5b83\u662f\u57fa\u4e8e\u51fd\u6570\u7684\u4e00\u6b3eHTML\u811a\u672c\u8bed\u8a00\u3002\u5e9e\u5927\u7684\u51fd\u6570\u5e93\u652f\u6301\u7740PHP\u8bed\u8a00\u529f\u80fd\u7684\u5b9e\u73b0\u3002\u4e0b\u9762\u6211\u4eec\u4e3a\u5927\u5bb6\u4ecb\u7ecd\u6709\u5173PHP\u51fd\u6570isset()\u7684\u76f8\u5173\u7528\u6cd5\u3002<\/p>\n

     <\/p>\n

    \u683c\u5f0f\uff1abool isset ( mixed var [, mixed var [, …]] )<\/p>\n

    \u529f\u80fd\uff1a\u68c0\u6d4b\u53d8\u91cf\u662f\u5426\u8bbe\u7f6e<\/p>\n

    \u8fd4\u56de\u503c\uff1a<\/p>\n

    \u82e5\u53d8\u91cf\u4e0d\u5b58\u5728\u5219\u8fd4\u56de FALSE
    \n\u82e5\u53d8\u91cf\u5b58\u5728\u4e14\u5176\u503c\u4e3aNULL\uff0c\u4e5f\u8fd4\u56de FALSE
    \n\u82e5\u53d8\u91cf\u5b58\u5728\u4e14\u503c\u4e0d\u4e3aNULL\uff0c\u5219\u8fd4\u56de TURE<\/p>\n

    \u540c\u65f6\u68c0\u67e5\u591a\u4e2a\u53d8\u91cf\u65f6\uff0c\u6bcf\u4e2a\u5355\u9879\u90fd\u7b26\u5408\u4e0a\u4e00\u6761\u8981\u6c42\u65f6\u624d\u8fd4\u56de TRUE\uff0c\u5426\u5219\u7ed3\u679c\u4e3a FALSE<\/p>\n

    \u7248\u672c\uff1aPHP 3, PHP 4, PHP 5<\/p>\n

    \u66f4\u591a\u8bf4\u660e\uff1a<\/p>\n

    \u4f7f\u7528 unset() \u91ca\u653e\u53d8\u91cf\u4e4b\u540e\uff0c\u5b83\u5c06\u4e0d\u518d\u662f isset()\u3002
    \nPHP\u51fd\u6570isset()\u53ea\u80fd\u7528\u4e8e\u53d8\u91cf\uff0c\u4f20\u9012\u4efb\u4f55\u5176\u5b83\u53c2\u6570\u90fd\u5c06\u9020\u6210\u89e3\u6790\u9519\u8bef\u3002
    \n\u68c0\u6d4b\u5e38\u91cf\u662f\u5426\u5df2\u8bbe\u7f6e\u53ef\u4f7f\u7528 defined() \u51fd\u6570\u3002<\/p>\n

      \n
    1. <<\/span><\/strong> ?php<\/li>\n
    2. $var<\/span> = ”<\/span>;<\/li>\n
    3. if (isset($var)) \/\/ \u7a7a\u503c\u30010\u3001false
      \n\u7684\u8d4b\u503c\u7ed3\u679c\u5747\u88abisset\u5224\u4e3a TRUE\uff0c\u6240\u4ee5\u540e\u8fb9
      \n\u7684\u6587\u672c\u5c06\u88ab\u6253\u5370\u51fa\u6765\u3002<\/li>\n
    4. print “blank value –><\/span><\/strong> isset<\/span> = true<\/span>. “;<\/li>\n
    5. $var<\/span> = NULL<\/span>;if (!isset($var)) \/\/
      \nNULL\u5c06\u88abisset\u5224\u4e3a FALSE<\/li>\n
    6. print “NULL value –><\/span><\/strong> isset<\/span> = false<\/span>. “;
      \n\/\/\u4ee5\u4e0b\u4f7f\u7528 var_dump \u8f93\u51fa isset() \u7684\u8fd4\u56de\u503c\u3002<\/li>\n
    7. $a<\/span> = “test”<\/span>;<\/li>\n
    8. $b<\/span> = “anothertest”<\/span>;<\/li>\n
    9. var_dump( isset($a) ); \/\/ TRUE<\/li>\n
    10. var_dump( isset ($a, $b) ); \/\/ TRUE<\/li>\n
    11. unset ($a);<\/li>\n
    12. var_dump( isset ($a) ); \/\/ FALSE<\/li>\n
    13. var_dump( isset ($a, $b) ); \/\/ FALSE<\/li>\n
    14. ?><\/span><\/strong><\/li>\n<\/ol>\n

       <\/p>\n

      PHP\u51fd\u6570isset()\u540c\u6837\u9002\u7528\u4e8e\u6570\u7ec4\u5143\u7d20\u548c\u5bf9\u8c61\u5143\u7d20\u7684\u68c0\u67e5\u3002\u82e5\u6570\u7ec4\u6216\u5bf9\u8c61\u5b9e\u4f8b\u672a\u88ab\u5b9a\u4e49\uff0c\u5219\u68c0\u6d4b\u5176\u4e2d\u7684\u6570\u7ec4\u5143\u7d20\/\u5bf9\u8c61\u5143\u7d20\u5c06\u88ab\u8fd4\u56defalse\u3002<\/p>\n

       <\/p>\n

        \n
      1. <<\/span><\/strong> ?php<\/li>\n
      2. $a<\/span> = array<\/span> (‘test’ =><\/span><\/strong> 1, ‘hello’ =><\/span><\/strong> NULL);<\/li>\n
      3. var_dump( isset ($a[‘test’]) ); \/\/ TRUE<\/li>\n
      4. var_dump( isset ($a[‘foo’]) ); \/\/ FALSE<\/li>\n
      5. var_dump( isset ($a[‘hello’]) ); \/\/ FALSE<\/li>\n
      6. \/\/ \u952e ‘hello’ \u7684\u503c\u7b49\u4e8e NULL\uff0c\u6240\u4ee5\u88ab\u8ba4\u4e3a\u662f\u672a\u7f6e\u503c\u7684\u3002<\/li>\n
      7. \/\/ \u5982\u679c\u60f3\u68c0\u6d4b NULL \u952e\u503c\uff0c\u53ef\u4ee5\u8bd5\u8bd5\u4e0b\u8fb9\u7684\u65b9\u6cd5\u3002<\/li>\n
      8. var_dump( array_key_exists(‘hello’, $a) ); \/\/ TRUE<\/li>\n
      9. ?><\/span><\/strong><\/li>\n<\/ol>\n

         <\/p>\n

        \u6ce8: \u7531\u4e8e\u8fd9\u662f\u4e00\u4e2a\u8bed\u8a00\u7ed3\u6784\u800c\u975e\u51fd\u6570\uff0c\u56e0\u6b64PHP\u51fd\u6570isset()\u65e0\u6cd5\u88ab\u53d8\u91cf\u51fd\u6570\u8c03\u7528\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"

        isset (PHP 3, PHP 4, PHP 5 ) isset...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[],"class_list":["post-148","post","type-post","status-publish","format-standard","hentry","category-phpjsshell"],"_links":{"self":[{"href":"https:\/\/www.01xj.net\/index.php?rest_route=\/wp\/v2\/posts\/148","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.01xj.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.01xj.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.01xj.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.01xj.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=148"}],"version-history":[{"count":1,"href":"https:\/\/www.01xj.net\/index.php?rest_route=\/wp\/v2\/posts\/148\/revisions"}],"predecessor-version":[{"id":149,"href":"https:\/\/www.01xj.net\/index.php?rest_route=\/wp\/v2\/posts\/148\/revisions\/149"}],"wp:attachment":[{"href":"https:\/\/www.01xj.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=148"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.01xj.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=148"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.01xj.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=148"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}