Why does my http_build_url () function Report an error?

Why does my http_build_url () function Report an error ;? Phpechohttp_build_url (& quot; http: // user@www.example.com/pub/index. php? A = B # files & quot;, & nbsp; array (& nbsp; & q Why does my http_build_url () function Report an error?
Echo http_build_url ("http: // user@www.example.com/pub/index. php? A = B # files ",
Array (
"Scheme" => "ftp ",
"Host" => "ftp.example.com ",
"Path" => "files/current /",
"Query" => "a = c"
),
HTTP_URL_STRIP_AUTH | HTTP_URL_JOIN_PATH | HTTP_URL_JOIN_QUERY | HTTP_URL_STRIP_FRAGMENT
);
?>
In the manual, no configuration is required and can be used directly. Why does my error cause Fatal error: Call to undefined function http_build_url () in E: \ wamp \ www \ sometimeExa \ buw._url.php on line 2

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(PECL pecl_http> = 0.21.0)
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Http_build_url
(PECL pecl_http: 0.21.0-1.5.5)

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Http://pecl.php.net/* nix

Windows http://downloads.php.net/pierre/
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The http_build_url function is affiliated with the pecl_http extension.
The extension of the PECL series does not belong to the php Standard configuration series and cannot be maintained by the php development organization.
If you do not have special requirements, do not use the PECL extension. If it is used, you need to pay close attention to the developer's website to promptly update and eliminate bugs.