Re: makefile for generating exe from single cpp

[Amit Chaudhuri]

Paul,

Thanks for making the logic and solution so clear.

Perfect.

A

On Sat, Oct 18, 2014 at 3:37 PM, Paul Smith <address@hidden> wrote:
>> On Fri, Oct 17, 2014 at 1:51 PM, Paul Smith <address@hidden> wrote:
>> > If you provide us the output of the make command we can be more helpful.
>
> On Sat, 2014-10-18 at 07:48 +0100, Amit Chaudhuri wrote:
>> address@hidden:~/prog/cpp/test> make -n
>> g++    -c -o main.o main.cpp
>> cc   main.o   -o main
>
> This is all I asked for, and all we needed to see.
>
> Here it's clear that make DOES use "g++" to compile your C++ file into
> a .o file, because make can see that in order to build a .cpp file into
> a .o file it needs to use a C++ compiler.
>
> However the next step, to turn a .o file into an executable, can be done
> in any of a large number of ways.  The .o file could be generated from a
> C compiler, C++ compiler, FORTRAN compiler, or various other types of
> compilers.  Since make can choose only one by default it chooses to use
> the C linker.
>
> There are various solutions depending on your situation.  If you really
> only have one source file and that's all you'll ever have, you can
> change your makefile like this:
>
>     main: main.cpp
>
> (have the executable depend on the source file not the object file).
> Now make can guess that it needs to use the C++ compiler and linker
> since it's doing things in one step.  And since you only have one file
> to compile anyway you're not losing any efficiency.
>
> If you have more than one source file, you should either change the
> built-in LINK.o variable to use the C++ compiler:
>
>     LINK.o = $(CXX) $(LDFLAGS) $(TARGET_ARCH)
>
>     main: main.o foo.o bar.o baz.o
>
> Or else write the link command explicitly:
>
>     main: main.o foo.o bar.o baz.o
>             $(CXX) $(CXXFLAGS) $(CPPFLAGS) $(LDFLAGS) -o $@ $^ $(LDLIBS)
>