Re: How to adding pathes to dependencies in rules of `.d` files

[Paul Smith]

On Sun, 2023-03-05 at 04:13 +0800, ljh wrote:
> 1. In thie out of source version, I can not omit recipes in both
> building and linking rules. This make it a bit complicated.

I'm not sure I understand the problem.  If the question is, is there a
way to use the normal built-in implicit rules for makefiles so you
don't have to add your own implicit rules, while still writing targets
to a different directory then the answer is "no".

If you want to write targets to some non-local directory you MUST
create your own implicit rules.

The only way to have targets written to a different directory from
sources AND still use the built-in implicit rules, is to invoke make in
the object directory, not the source directory.  Then you can write
targets to the current directory, and use VPATH to locate sources in
some other directory.

> 2. if I put # comment at the end of the line of export OBJDIR, it
> causes mysterious error message in rules involve the variable.

In makefiles, whitespace BEFORE the start of a value in an assignment
is stripped.  But whitespace AFTER the end of a value in an assignment
is not stripped, it's preserved.

So this line:

  A =       B# this is some value

Sets the variable "A" to the value "B".  But this line:

  A =       B #this is some value

Sets the variable "A" to the value "B " (note the space).

In general it's a bad idea to use inline comments in makefiles,
particularly in variable assignments.