代码如下：
unsigned int pathSize = GetEnvironmentVariableA("ALLUSERPROFILE", pName, BUFFER_SIZE);
参数：
USERPROFILE =c:\users\xxx HOMEPATH =c:\users\xxx APPDATA =c:\users\xxx\AppData\Roaming LOCALAPPDATA=c:\users\xxx\AppData\Local //默认的。吾都会将之改到C:\Temp下 TEMP =c:\users\xxx\AppData\Local\Temp TMP =c:\users\xxx\AppData\Local\Temp ALLUSERSPROFILE=c:\ProgramData
下面这个链接，感觉什么用也没有。
https://docs.microsoft.com/en-us/windows/deployment/usmt/usmt-recognized-environment-variables
