Question

Is it the C preprocessor, compiler, or linkage editor?

Answer 1

The answer you are looking for is… the compiler it depends. Sometimes it’s the compiler, sometimes it’s the linker, and sometimes it doesn’t happen until the program is loaded.

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The preprocessor:

handles directives for source file inclusion (#include), macro definitions (#define), and conditional inclusion (#if).
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The language of preprocessor directives is agnostic to the grammar of C, so the C preprocessor can also be used independently to process other kinds of text files.

The linker:

takes one or more objects generated by a compiler and combines them into a single executable program.
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Computer programs typically comprise several parts or modules; all
these parts/modules need not be contained within a single object file,
and in such case refer to each other by means of symbols. Typically,
an object file can contain three kinds of symbols:

• defined symbols, which allow it to be called by other modules,
• undefined symbols, which call the other modules where these symbols are defined, and
• local symbols, used internally within the object file to facilitate relocation.

When a program comprises multiple object files, the linker combines
these files into a unified executable program, resolving the
symbols as it goes along.

In environments which allow dynamic linking, it is possible that

executable code still contains undefined symbols, plus a list of objects or libraries that will provide definitions for these.