compilation how to - What's an object file in C?

2 Answers

  1. An Object file is the compiled file itself. There is no difference between the two.

  2. An executable file is formed by linking the Object files.

  3. Object file contains low level instructions which can be understood by the CPU. That is why it is also called machine code.

  4. This low level machine code is the binary representation of the instructions which you can also write directly using assembly language and then process the assembly language code (represented in English) into machine language (represented in Hex) using an assembler.

Here's a typical high level flow for this process for code in High Level Language such as C

--> goes through pre-processor

--> to give optimized code, still in C

--> goes through compiler

--> to give assembly code

--> goes through an assembler

--> to give code in machine language which is stored in OBJECT FILES

--> goes through Linker

--> to get an executable file.

This flow can have some variations for example most compilers can directly generate the machine language code, without going through an assembler. Similarly, they can do the pre-processing for you. Still, it is nice to break up the constituents for a better understanding.

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I am reading about libraries in C but I have not yet found an explanation on what an object file is. What's the real difference between any other compiled file and an object file?
I would be glad if someone could explain in human language.

An object file is just what you get when you compile one (or several) source file(s).

It can be either a fully completed executable or library, or intermediate files.

The object files typically contain native code, linker information, debugging symbols and so forth.