The unnamed language that is compiled by cc.

To elaborate... C[++] is really two different languages, with mostly distinct feature sets, handled in most cases by different compilers, interpreters, parsers, etc.

The unnamed language with keywords like #ifdef and #include which produces text output is a templating system that is functionally independent of the unnamed language with keywords like for and unsigned which actually compiles to a binary.

You can use cpp to run all the logic and conditionals in that first language to produce output, even if you replace the second language with something else like python or assembly.

You can use cc to compile that second language from source to binary, without support from the preprocessor.

That second language, the one that cc understands and compiles, does not have the ability to import functions or values or whatever from other files.