O File

What are O files and how to open them

Are you having problems opening an O file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your O files.

What is an O file?

O files have multiple uses, and Common Object File Format (COFF) Object is one of them. Read more about the other uses further down the page.

Common Object File Format (COFF) Object File

Several compilers generate these files on the Windows platform, e.g., C and C++ compilers. When the compiler processes a source code file, a .obj file is generated. When all source code files have been compiled to .obj files, the .obj files are linked together to the resulting .exe executable file or .dll library file.

These files also commonly use the .obj file extension.

How to open O files

Important: Different programs may use files with the O file extension for different purposes, so unless you are sure which format your O file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested four different O openers which you will find listed below.

Last updated: June 29, 2022

All known file formats using extension .O

While Common Object File Format (COFF) Object File is a popular type of O-file, we know of 8 different uses of the .O file extension. Different software may use files with the same extension for different types of data.

Executable and Linkable Format (ELF) Object File

These files have the same function on Unix and Linux systems running on x86 processors, as files in the Common Object File Format have on Windows PCs. It is a different standard for a different operating system, but feature-wise it is pretty much the same.

When a developer compiles his source code into a program, one object file is generated per source code file. When developing on Unix and Unix-like systems, these are in ELF object format.

Relocatable Object Module Format (OMF) Object File

These files have the same function on MS-DOS, 16-bit Windows or OS/2 systems running on 8086 processors, as files in the Common Object File Format have on 32- and 64-bit Windows PCs. It is a different standard for different operating systems, but feature-wise it is pretty much the same.

When a developer compiles his source code into a program, one object file is generated per source code file. When developing on MS-DOS, OS/2, or 16-bit Windows systems, these are in OMF object format.

Intel 80386 Common Object File Format (COFF) Object / Library

We know that one O format is Intel 80386 Common Object File Format (COFF) Object / Library. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Intel AMD64 Common Object File Format (COFF) Object / Library

We know that one O format is Intel AMD64 Common Object File Format (COFF) Object / Library. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Intel IA64 Common Object File Format (COFF) Object / Library

We know that one O format is Intel IA64 Common Object File Format (COFF) Object / Library. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Mac OS X Mach-O Universal Object Code

We know that one O format is Mac OS X Mach-O Universal Object Code. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Mac OS X Universal Binary

We know that one O format is Mac OS X Universal Binary. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Various apps that use files with this extension

These apps are known to open certain types of O files. Remember, different programs may use O files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about O file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.