# Universal Paths

TADS has a "universal" syntax for file names that include directory paths. TADS translates from the universal notation to the local file system syntax automatically, so you don't have to worry about whether your Windows "X:\Y\Z" paths will work on a Linux machine, or vice versa.

TADS accepts the universal path syntax in several places:

- #include directives in TADS source files
- File names in .t3m project files
- File and directory option arguments in .t3m files (-I, -o, -Os, -FL, -FI, -Fs, -Fy, -Fo, -Fa)
- File.universalToLocal()

In all of these situations, when you specify a directory path to a file, you should use the universal notation instead of your local system's file path syntax. TADS will translate for you, using the appropriate local conventions. This will make your code work the same way everywhere TADS runs, without having to make changes when moving the code to a new system.

## Universal path rules

Path separators: "/" is the path separator. For example, to include a file defs.h from subdirectory inc, you'd write #include "inc/defs.h".

Relative paths: For portability, use relative paths whenever possible. "Relative" means that the path is interpreted starting from the current working directory or some other context. In the case of #include, relative paths are relative to the folder containing the source file with the #include directive; for .t3m files, paths are relative to the .t3m file's location.

Relative paths improve portability because they adapt automatically to different machines' directory structures. If you move the program to a new machine, you only have to reproduce the subdirectories of the main program folder - everything is relative to that folder, so it's all self-contained. Importantly, it doesn't matter where that main folder is situated within the system's overall directory structure. If you keep the project in C:\My Documents\games\tads on your Windows machine, and you send it to someone who puts it in /home/projects on her Linux machine, the difference in absolute location doesn't matter; it's only what's inside that directory that matters.

Current and parent paths: The universal notation defines "." and ".." to have the same meanings they do on Unix and Windows. "." is the current directory; as part of a path, it just reiterates the preceding element, and as the first element of a path it explicitly refers to the current directory. ".." is the parent of the preceding path element, or the parent of the current directory when ".." appears at the start of a path.

For example, ../games/deep.gam in the universal path notation will translate on classic Mac OS to ::games:deep.gam.

Absolute paths: In some cases it's not possible to use a relative path. You should use relative paths when you can, but when you can't, the universal notation can also accommodate "absolute" paths. An absolute path specifies an exact, fixed location in the local file system.

In the universal notation, an absolute path always starts with "/". On systems like Windows that use a volume prefix (e.g., "C:"), write the volume prefix as the first path element. Include the full local syntax - in the case of a Windows drive letter, include the colon. For example, the Windows path C:\games\deep.gam becomes /C:/games/deep.gam in the universal notation.

The reason you should avoid absolute paths is that they're inherently non-portable - not just between operating systems, but even between two machines running the same OS. An absolute path is dependent upon the exact disk layout of your machine; if you take a file containing an absolute path to someone else's machine, chances are that their disk layout will be slightly different, so you'll probably have to rewrite the absolute path to match their directory structure. That largely defeats the purpose of using the universal path syntax in the first place.

## Examples

System | Local Path | Universal Path
--- | --- | ---
Windows | games\deep\deep.gam | games/deep/deep.gam
Linux | games/deep/deep.gam | games/deep/deep.gam
Windows | ..\deep.gam | ../deep.gam
Classic Mac OS | ::deep.gam | ../deep.gam
Classic Mac OS | :: | ..
Classic Mac OS | ::: | ../..
VMS | [-.DOCS]DEEP.GAM | ../DOCS/DEEP.GAM
Linux | /home/games/deep.gam | /home/games/deep.gam
Windows | c:\user\games\deep\deep.gam | /c:/user/games/deep/deep.gam
Windows | \\SERVER\SHARE\games\deep.gam | /\\SERVER/SHARE/games/deep.gam
Classic Mac OS | Mac HD:games:deep.gam | /Mac HD:/games/deep.gam
VMS | SYS$DISK:[USER.DOCS]DEEP.GAM | /SYS$DISK:/USER/DOCS/DEEP.GAM

TADS 3 System Manual
Table of Contents | The Tools > Universal Paths
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