O, Compiled Object File (.o)
The O Developer file format
Some files that are creating during the development process of a program or software are not directly linked to a specific program or even function. One such file is the O file format. Files of this very short extension are created by a C compiler, for example, the GNU Compiler Collection (GCC). It may happen that, during the programming process, a file is not saved as a proper program file. In these cases, it’s possible that the O object file is created instead. Afterwards, they can be linked together again to generate the actual executable file.
Technical details of O files
O files contain C or C++ code that the compiler used to create the file is using to process other source code files. The O files contain code that is more compact, which is often referred to as binaries. With a so-called linker, these files can be linked to generate a library or executable file. The O file extension is known as a general object file. This means it is associated with many different compilers and programs. This includes the pascal compiler Free Pascal and Xcode which is used to create applications for the Mac OS X operating system.