Re: Request for critique on a small makefile

[Edward Z. Yang]

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Philip Guenther wrote:
> First off, you should take a look at Paul Smith's rules for makefiles:
>     http://make.paulandlesley.org/rules.html
> 
> You current makefile violates rules 2, 3, and 4 from that page.

Okay, I've read it, they seem to be very common sense rules, let's see
if I can see how they were applied.

> Rather than try to do a line-by-line analysis, let me show how I would
> write the makefile for building those two programs:
> 
> boostdir = /usr/include/boost-1_33_1
> boostlib = -lboost_program_options-gcc-mt-s
> 
> # these next two variables are used by make's builtin pattern rules
> CXXFLAGS = -ansi -pedantic
> CPPFLAGS = -I${boostdir}
>
>
> programs = fibonacci printNumbers
> 
> all : ${programs}
> 
> clean:
>        ${RM} ${programs} *.o

Regarding number two, these two don't edit $@, does that mean we need a
.PHONY rule?

> fibonacci: fibonacci.o
>        ${LINK.cc} -o $@ $< ${boostlib}

A lot of variables used here.
${LINK.cc} is a macro for a C++ linker with all the options we specified
above
$@ is the target of the rule
$< are the prerequisites (one or all of them?)
${boostlib} is the var we stated

> Notes:
> - the source files aren't mentioned at all.  Instead, I practice my
> laziness and let make's pattern rules figure out how to create the .o files
> - as it traditionaly under UNIX, the executables don't have a .exe
> suffix.  If you *really*
>   want the suffix, you would do the following:
>   1) change the value of the 'programs' variable
>   2) add the .exe suffix to just the target in the rule for linking
> fibonacci
>   3) add a rule for linking printNumbers.exe similar to the one for
> fibonacci.exe

I'm running GNU make of a cygwin compatibility layer. As is, the
executables are magically getting .exe suffixes, breaking `make clean`.
How do I fix this?

> - the object files are left in the current directory.  Don't change
> this without first
>   reading all of Paul's webpages on Make at http://make.paulandlesley.org/

Okay. I read somewhere else that objects should be put in another
directory, but I'll read more about multi-architecture VPATH method
before doing it.

> Here's the output of make -n with that makefile in a directory
> containing files fibonacci.cpp and printNumbers.cpp:
> 
> $ gmake -n
> g++ -ansi -pedantic -I/usr/include/boost-1_33_1  -c -o fibonacci.o
> fibonacci.cpp
> g++ -ansi -pedantic -I/usr/include/boost-1_33_1   -o fibonacci
> fibonacci.o -lboost_program_options-gcc-mt-s
> g++ -ansi -pedantic -I/usr/include/boost-1_33_1   printNumbers.cpp
> -o printNumbers

Regarding the auto-exe output, when I run `make -n`, I get the same
result, so it's not g++'s fault. Cygwin?

Also, is gmake the name of your make executable or simply an alias to
make to make sure any other programs named make don't conflict?

> If you aren't sure what pattern rules or variables are builtin to your
> copy of GNU make, you can dump the entire set using the following
> command:
> 
> gmake -pq -f/dev/null
> 
> That generates 1085 lines of output on my system, so you may want to
> redirect it to a file or pipe it to 'less'...

Good to know.  I have found
<http://www.gnu.org/software/make/manual/html_node/Name-Index.html> to
be slightly more useful, though.

> Does that help at all?

Definitely.

- --
 Edward Z. Yang      Personal: address@hidden
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