Object file (Unix)
O is a file extension for an object file used with Unix and Linux systems. O stands for object. O files contain C or C++ source code to be compiled into an application. O files can be opened by GCC (GNU C and C++ Compiler) on Unix and Linux systems, and Microsoft Visual Studio on Windows systems.
MIME type: application/x-object-file; application/x-object
Learn more about .O files:
See our C, C++ and C# Cheat Sheets.
Visit the C++ web page.
Read the C FAQ at ITKnowledgeExchange.com.