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File Extensions

In Unix and Linux file extensions are a matter of convenience, while in Windows the three-letter extension identifies what type of file it is, or determines which application "owns" a file.

  • Registry is where extensions are matched up with applications. (Consider this information to be FYI only; we don't recommend editing the registry.)
  • File appears with correct icon and opens by double-clicking if the registry can match the suffix with the right application.
    Plus side: you can tell what a file is by looking at its name
    Minus side: you might need to rename file extensions to open them
  • To see the list of file types and associated applications and change these associations if necessary: Open the Settings > Control Panel > Folder Options > File Types

Common extensions:

Common extensions:
Applications (executables): .exe
Fortran source: .for
C source: .c
C++ source: .cpp
Object file: .obj
Dynamic link library: .dll
Batch file: .bat
Plain text file: .txt
MS Word document: .doc

File extensions are much more important in Windows than in Unix or Linux. In Unix and Linux the file extensions are a matter of convenience, while in Windows the three-letter extension identifies what type of file it is, or determines which application "owns" a file. For example, you might like to call your plain text files .doc for document, but in Windows that file will automatically be opened with Microsoft Word, because that's the default for that extension. There are cases where the operating system or application program can become confused if you have the wrong file type. Avoid trouble by using the expected extension.

  • Registry is where extensions are matched up with applications. (Consider this information to be FYI only; we don't recommend editing the registry.)
  • File appears with correct icon and opens by double-clicking if the registry can match the suffix with the right application.
    Plus side: you can tell what a file is by looking at its name
    Minus side: you might need to rename file extensions to open them
  • To see the list of file types and associated applications and change these associations if necessary: Open the Settings > Control Panel > Folder Options > File Types
Common extensions:
Applications (executables): .exe
Fortran source: .for
C source: .c
C++ source: .cpp
Object file: .obj
Dynamic link library: .dll
Batch file: .bat
Plain text file: .txt
MS Word document: .doc