Php+iis virtual Directory is invalid

The great gods have just contacted PHP, and I'm using IIS to set up a virtual directory upload use file_exists or is_file to detect if the file exists is returned false
Website Absolute path is: D:\web\
Upload virtual directory absolute path is: E:\upload
Now with Is_file detection is not the path of the virtual directory is still the absolute path of the site D:\web\upload how can I set up to implement detection E:\upload?

Reply to discussion (solution)

A virtual directory is a WEB system that consolidates directories that are not in the default jurisdiction (including directories on other machines) into the current site
File_exists such as file system functions, it is not possible to proactively identify the virtual directory of the Web system
You can
1, write the full path
2, temporarily change the working path of PHP
3. Add the absolute path of the virtual directory to the Include_path

Define (' Upload_path ', ' E:\upload ');
The absolute path is obtained when uploading.

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