NSIS，判断安装包是否管理员身份运行的代码

本篇文章属于《518超市播音软件开发日志》系列文章的一部分。
我在开发《518超市播音软件》（http://www.518boyin.com/）的时候，用的NSIS打包制作安装包，安装的时候，需要确保是管理员权限的，不是的话，就提示需要管理员权限运行，然后退出。
Function un.onInit
Call un.IsUserAdmin
Pop $R0
${If} $R0 == "false"
MessageBox MB_ICONEXCLAMATION|MB_OK|MB_TOPMOST|MB_SETFOREGROUND "需以管理员身份运行 $\n"
Quit
${EndIf}
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; Usage:
; Call IsUserAdmin
; Pop $R0 ; at this point $R0 is "true" or "false"
;
Function IsUserAdmin
Push $R0
Push $R1
Push $R2
ClearErrors
UserInfo::GetName
IfErrors Win9x
Pop $R1
UserInfo::GetAccountType
Pop $R2
StrCmp $R2 "Admin" 0 Continue
; Observation: I get here when running Win98SE. (Lilla)
; The functions UserInfo.dll looks for are there on Win98 too,
; but just don't work. So UserInfo.dll, knowing that admin isn't required
; on Win98, returns admin anyway. (per kichik)
; MessageBox MB_OK 'User "$R1" is in the Administrators group'
StrCpy $R0 "true"
Goto Done
Continue:
; You should still check for an empty string because the functions
; UserInfo.dll looks for may not be present on Windows 95. (per kichik)
StrCmp $R2 "" Win9x
StrCpy $R0 "false"
;MessageBox MB_OK 'User "$R1" is in the "$R2" group'
Goto Done
Win9x:
; comment/message below is by UserInfo.nsi author:
; This one means you don't need to care about admin or
; not admin because Windows 9x doesn't either
;MessageBox MB_OK "Error! This DLL can't run under Windows 9x!"
StrCpy $R0 "true"
Done:
;MessageBox MB_OK 'User= "$R1" AccountType= "$R2" IsUserAdmin= "$R0"'
Pop $R2
Pop $R1
Exch $R0
FunctionEnd
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