GCC preprocessing, what are the built-in and command-line tools for?

Question

I am interested to know about the release of the GCC preprocessing phase. More precisely, what is the purpose of the following two lines:

# 1 "<built-in>"
# 1 "<command line>"

I know the format <line_number> <file name> <flags>, but I do not understand what data types may appear in this section. What is his purpose?

Thank!

Answer 1

The goal is to keep track of the source source string, which leads to code expansion. This, for example, is used when you are compiling with debugging to tell the debugger the lines of code you step through.

In your particular case, you seem to have captured lines at the start of compilation before gcc even started processing the input file.