phony | E164 international phone number normalizing splitting

You need to modify the makefile inorder to adapt C++:
You need to change CFLAGS to CPPFLAGS See below reference example:

It would be helpful if you showed a small example with a few actual filenames and the actual output you get when you run make. I can see no obvious reason in this makefile why it should stop with one file, unless all the other files already exist and are up to date.

I do see something strange but since I don't know anything about how pdflatex works, maybe it's expected:

You need to examine the section on How Patterns Match where you will find this text:

When the target pattern does not contain a slash (and it usually does not), directory names in the file names are removed from the file name before it is compared with the target prefix and suffix.

(and more detail about how this works).

Makefile is a utility for writing and executing series of command-line instructions for things like compiling code, testing code, formatting code, running code, downloading/uploading data, cleaning your directory etc ... Basically, it helps automate your dev workflows into simple commands (make run, make test, make clean).

Here's what it does in this case:

Most likely because your sources variable src is empty. Which means your objects list variable obj is empty. Which means that your library lib/btree.a doesn't depend on anything, so make doesn't build anything.

This is most likely because this:

The problem is that $(SRC:.c =.o) doesn't work because of that space (there are no SRC names ending with ".c " (including the last space).

It should be $(SRC:.c=.o).

The answer is strictly due to make's rules and has nothing to do with any of the other tags here (I'll remove all the others). The makefile that doesn't work says:

• to build gitbranch-foo, we must build git-spawn-branch
• to build gitbranch-bar, we must build git-spawn-branch

(plus of course the code for building git-spawn-branch itself and the other associated stuff, but let's stop here).

You then run make, telling it to build both gitbranch-foo and gitbranch-bar.

Make picks one of these to build—gitbranch-foo, in this case—and begins building. Oh hey, says make to itself, this needs git-spawn-branch to be built, and we have not done that yet. Off goes make, which builds git-spawn-branch according to the rules. Now it's built! Make can go back to building gitbranch-foo. This executes the remaining recipe, which is empty.

If parallel builds are allowed, make can also now begin building gitbranch-bar while gitbranch-foo builds. If not, we wait for gitbranch-foo to be fully built at this point. Either way we very quickly get around to buildling gitbranch-bar. Hm, says make to itself, this needs git-spawn-branch to be built ... but fortunately, I have done that already! Onward! Let's make the rest of gitbranch-bar now! That requires executing the empty recipe, which goes very quickly.

Make is now done. It has built everything required.

(The makefile that works uses $call sensibly, directly from each rule, so that the commands that $call expands to are required to be run for each target, rather than hidden away in a third target that can be built just once and never needs to be run any further.)

(Note that the gmake documentation mentions that a .PHONY rule is run every time. This means once per invocation of make, not once per invocation of the rule.)

Your object file recipes don't have any dependencies associated with them, so they won't get built unless you specify them explicitly.

Add the .c files to the dependency lists:

You have this: