Re: Additional environment information with make 4

[Markus Fischer]

Hi Christian,

some of this I knew, but didn't use it in the example because it wasn't
necessary to illustrate my problem. Thank you for taking the time to
explain this. That's awesome!

On 06.03.2015 14:24, Christian Hujer wrote:
> Hi Markus,
> 
> there are a few things you can improve about your little Makefile.
> 
> Short:
> * avoid '@' - instead use -s
> * Use the built-in rules, they're good
> * Follow the conventions of the built-in rules to make them work
> * Declare non-file goals .PHONY
> * Tell make about dependencies to make it run incrementally
> * Add a clean rule to remote the stuff that make was building
> 
> Long:
> * I recommend to avoid '@' and use it only in rare cases.
> Sooner or later you will have a Makefile which doesn't run as
> expected, either by itself or because one of the commands that it
> calls is hanging.
> Then you will be thankful for the command echo.
> You will not want to have to change the Makefile and remove the '@' on
> all the recipes just in order to see what's going on.
> 
> Instead, use the `-s` command line option.
> With '-s' you can tell make that you're not interested in seeing
> what's going on.
> And if that's the usual case, you can define an environment variable like 
> this:
> export MAKEFLAGS=-s
> 
> See also https://www.gnu.org/software/make/manual/make.html#Echoing
> 
> * Use the built-in rules, they're good.
> An overview of the built-in rules can be seen here:
> https://www.gnu.org/software/make/manual/make.html#Catalogue-of-Rules
> So, make already knows how to compile C++ programs, you don't need to tell it.
> Also, I find it useful to keep what to build (rules which specify
> dependencies) and how (pattern-rules which specify recipes) separate
> from each other.
> 
> * Follow conventions of the built-in rules to make them work
> The built-in rules expect that one of the object files has the same
> basename as the binary that you are trying to build.
> So, instead of building example from main.cpp, you would build example
> from example.cpp.
> This is a convention which is also there outside the world of make.
> It's quite common practice to name the source file that contains main
> after the intended program name.
> 
> The following Makefile is sufficient to tell make to compile
> example.cpp into example:
> 
> all: example
> 
> No further line is needed, make knows the rest by itself.
> 
> * Declare non-file goals .PHONY
> It's recommended to declare goals which do not exist as a file as .PHONY.
> This prevents the Makefile from falling over in case the user creates
> a file or directory with the same name as one of these goals.
> 
> So, above all rule should actually look like this:
> 
> .PHONY: all
> all: example
> 
> * Tell make about dependencies to make it run incrementally.
> For example, if you run `make run`, it would fail unless you ran `make` first.
> Why not tell make that if you want to `make run` and example doesn't
> exist, that example needs to be made first?
> 
> Change
> run:
>         ./example
> to
> .PHONY: run
> run: example
>         ./example
> 
> Now make knows that if you want to run, it first has to build.
> It would also rebuild in case example.cpp is newer than example.
> 
> * Add a clean rule to remove the stuff that make was building.
> 
> So here's your final Makefile:
> .PHONY: all
> all: example
> 
> .PHONY: run
> run: example
>         ./example
> 
> .PHONY: clean
> clean:
>         $(RM) example
> 
> I hope this helps you in your future ventures with make.
> 
> On Thu, Feb 26, 2015 at 6:33 PM, Markus Fischer <address@hidden> wrote:
>> On 26.02.2015 13:20, David wrote:
>>> Explained here:
>>> https://www.gnu.org/software/make/manual/html_node/Echoing.html#Echoing
>>>
>>> Try changing that line in your makefile to:
>>> <tab>@./example
>>>
>>
>> Thanks, this got me on the right path.
>>
>>
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