.O File Extension
Compiled C Object File
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What is an O file?
When compiling a C program, compilers first transform all the program's source code files into compiled object files. These compiled files typically use the .o or .OBJ extension. The compiler then links the compiled object files into an executable file.
Some examples of compilers that produce O files include GNU Compiler Collection (GCC)'s C and C++ compilers and Tiny C Compiler.
How to open an O file
C and C++ compilers, such as GCC and Tiny C Compiler, often create, reference, and use O files during the program compilation process. For example, you can use Tiny C Compiler's -o command to link O files together and create an executable.