PHP $_server[' document_root ' issues

$_server[' document_root ' value is empty, but there is actual data on the phpinfo () test page, which is the problem with my program? Or a problem with the configuration?
/*
Test program
Call base_info.php
*/
Print_r ($_server);
$SYSTEM _root_path = $_server[' document_root ');
#echo $_server[' Document_root ']. " \ n ";
echo $SYSTEM _root_path;
/*
Include ("$SYSTEM _root_path\lib\base_info.php");

$class = new Base_info ();

$S _info = $class->system_info ();
foreach ($key as $value) {
echo "$key ======== $value". \ n ";
}
*/

$_server Array Output
[AllUsersProfile] = C:\ProgramData
[Ant_home] = D:\hadoop\apache-ant-1.9.2
[APPDATA] = C:\Users\yjn\AppData\Roaming
[CLASSPATH] =,;D: \hadoop\java/lib/dt.jar;d:\hadoop\java/lib/tools.jar
[CommonProgramFiles] = C:\Program files (x86) \common files
[CommonProgramFiles (x86)] = C:\Program files (x86) \common files
[CommonProgramW6432] = C:\Program Files\Common Files
[COMPUTERNAME] = yjn-pc
[ComSpec] = C:\Windows\system32\cmd.exe
[Fp_no_host_check] = NO
[Homedrive] = C:
[HomePath] = \users\yjn
[Java_home] = D:\hadoop\Java
[LocalAppData] = C:\Users\yjn\AppData\Local
[LogonServer] = \\YJN-PC
[Number_of_processors] = 2
[OS] = Windows_NT
[Path] = C:\Perl64\site\bin; C:\Perl64\bin; C:\Windows\system32; C:\Windows;
Ndows\system32\wbem; C:\Windows\System32\WindowsPowerShell\v1.0\;D: \hadoop\j
In;d:\hadoop\java/jre/bin;d:\hadoop\apache-ant-1.9.2\bin;d:\php5;d:\php5\ex
[Pathext] =. COM;. EXE;. BAT;. CMD;. VBS;. VBE;. JS;. JSE;. WSF;. WSH;. MSC
[Processor_architecture] = x86
[processor_architew6432] = AMD64
[Processor_identifier] = Intel64 Family 6 Model stepping, Genuinein

[Processor_level] = 6
[Processor_revision] = 170a
[ProgramData] = C:\ProgramData
[ProgramFiles] = C:\Program Files (x86)
[ProgramFiles (x86)] = C:\Program Files (x86)
[ProgramW6432] = C:\Program Files
[PROMPT] = $P $g
[Psmodulepath] = C:\Windows\system32\WindowsPowerShell\v1.0\Modules\
[Public] = C:\Users\Public
[SessionName] = Console
[SystemDrive] = C:
[SystemRoot] = C:\Windows
[TEMP] = C:\Users\yjn\AppData\Local\Temp
[TMP] = C:\Users\yjn\AppData\Local\Temp
[UserDomain] = yjn-pc
[USERNAME] = Yjn
[UserProfile] = C:\Users\yjn
[windir] = C:\Windows
[Windows_tracing_flags] = 3
[Windows_tracing_logfile] = C:\BVTBin\Tests\installpackage\csilogfile.log
[Php_self] = test.php
[Script_name] = test.php
[Script_filename] = test.php
[Path_translated] = test.php
[Document_root] =
[Request_time] = 1381282125
[argv] = = Array
(
[0] = test.php
)

[ARGC] = 1

Reply to discussion (solution)

$_server[' Document_root '] needs to be specified in the server configuration, are you sure phpinfo has this value?

You $_server the array output [' document_root '] is obviously empty.

It is true that this value can be reached in phpinfo. It's strange that I don't know if there's a problem in the code
Settings in the httpd.conf
DocumentRoot "D:\Apache\htdocs"


_server["Document_root"] D:/apache/htdocs

You $_server the array output [' document_root '] is obviously empty.
I just want to know why it's empty?

echo $_server["Document_root"];

Personally feel that should not be entangled in $_server[' document_root ']
This variable does not pass through the server, it is not necessary to change a server to check the wrong and rewrite the code
Recommended with __file__ or __dir__

If you really need to know why, go to check the information, reportedly virtual machine with this variable is also a problem, no environmental measurement

