Is the preprocessor, assembler and linker a part of the compiler?

Question

So I've been taught, as many of us have, that the compiler is a program that translates your human readable code into machine readable code. The more you look into it however, you learn that the "compilation process" is actually broken up into 4 different parts: the preprocessor, compiler, assembler and linker. I think not understanding where all these parts fit into place have confused me a bit.

1. Are all the steps described in a typical compilation process part of the compiler program?
2. Or are things like the assembler and linker separate programs built into IDE's along with compilers to generate code?
3. Does it depend on the compiler or programming language?
4. If separate, is the compiler responsible for just the assembly code creation as well as optimizing the assembly code?

Answer 1

Are all the steps described in a typical compilation process part of the compiler program?

All the steps are required by the translation process. The process includes Preprocess, Compilation, assembly / machine code instruction generation, and producing an executable (e.g. linking).

A translator program, a.k.a. compiler, does not need to put all steps into one compiler executable.

For example, a program may be composed of more than one translation unit, so they can be compiled all at once, then the pieces can be linked together. Often separating compilation from linking is beneficial.

Or are things like the assembler and linker separate programs built into IDE's along with compilers to generate code?

Some IDE's like Eclipse, do not have built-in compilers or linkers. The Eclipse IDE is designed to work with various compilers and linker. The Eclipse IDE needs to be configured as to what tools it will use when building a program.

Does it depend on the compiler or programming language?

IDEs are usually independent from compilers and languages. The NetBeans IDE can be used with Java or C++ (similarly with Eclipse).

Some IDEs may have features that work better with one language than another, such as keyword highlighting.

If separate, is the compiler responsible for just the assembly code creation as well as optimizing the assembly code?

Assembly language creation is not a required part of the process.

Typically, compilers have an option you can supply in order to print an assembly language listing.

Some compilers emit executable code without going through the generation of assembly language.

Answer 2

The meaning of the term “compiler” depends on the context.

For the beginner, the compiler is the tool you use to create an executable program from your source code.

Delving a little deeper, one learns that with practical toolchains there is at least a division into compiler and linker.

And while the above two views have been based solely on tool usage, when one learns more about C++ one appreciates the division into preprocessing and compilation “proper”, i.e. a preprocessor and a compiler, and a linker, where the preprocessor produces text, the compiler produces object code, and the linker produces executables or libraries.

Delving even deeper into things one may start to differentiate between different internal phases of the compiler (in the trio above). Some compiler utilize an assembler, some generate code directly from an abstract syntax tree, some compilers go as far as using a whole C compiler at the end, just translating the language X source code to C source code. E.g. Eiffel compilers used to do this, and probably do it still. And C++ started out that way, as a front end to a C compiler.

And especially with the idea of just translating to C, one may call that part the real compiler, with the C compiler at the end as just one of the tools invoked by the compiler proper.

So, it depends very much on the context.