Post on 17-Jan-2016
Copyright © 2015 Curt Hill
MakeAn Indispensable Developer’s
Tool
Introduction• Make is the name of a “scripting
language” interpreter – Designed specifically for compiling and
linking a programming project
• Originally a UNIX program• Has escaped the UNIX ecosystem and
is now everywhere• Refers to any of a set of programs that
do approximately the same thing• Every IDE either uses an existing
make or has a custom one
Copyright © 2015 Curt Hill
Components• There are typically two
– The program itself– The script file that describes the
executable build process• This often has the name make or makefile• With or without an extension
Copyright © 2015 Curt Hill
Process• Making a project is a matter of
checking dependencies and dates• A dependency exists when one file
depends upon another• Thus the executable usually depends
upon object files– Object files depend upon source files
• If an item is older than what it depends upon it must be rebuilt
Copyright © 2015 Curt Hill
Example• Suppose x.exe depends upon x.obj,
date.obj and classy.obj• When make is executed it finds that
x.exe is newer than data.obj and x.obj but older than classy.obj
• It now knows that it must re-link x.exe so as to incorporate the new class.obj
• It does the same process for obj files that depend on source files– Thus it only compiles and/or links what is out
of date
Copyright © 2015 Curt Hill
Statement Types• Comments – not really a statement• Assignments• Directives• Implicit rules• Explicit rules
Copyright © 2015 Curt Hill
Syntax• Comments are indicated by an
octothorp (#)– These are ignored– Standard UNIX scripting practice
• Assignment statement has a mostly standard format– Variable = expression– The expression does not necessarily
look like a C style expression– Often files separated by blanks
Copyright © 2015 Curt Hill
Explicit Rules• General form is two linestarget: dependencies[tab] system commands
• Targets are typically executables or object files– Other things possible
• The dependencies are one or more files that the target needs to be built
• The command is how to accomplish it
Copyright © 2015 Curt Hill
Explicit Rules Again• The usual form is target as a file:xyz.o: xyz.cpp classy.h [tab] gcc –c xyz.cpp
• If either classy.h or xyz.cpp is newer than xyz.o or if xyz.o does not exist then gcc with the c option is run on xyz.cpp
Copyright © 2015 Curt Hill
Target • Usually the target is a file like that
previously shown• Does not have to be a real file• We could do something like:all: xyz.cpp classy.cpp[tab]gcc xyz.cpp classy.cpp
• The normal execution of gcc will produce xyz.exe not all or all.exe
Copyright © 2015 Curt Hill
The $ • The $ function is an inclusion of variable’s
value• Form: $(variable)• Thus if we have:CPP = g++.exe
• Then we later see:$(CPP) -c ggapp.cpp
• This becomes the command line:g++.exe -c ggapp.cpp
• We can now easily change compilers or set options
Copyright © 2015 Curt Hill
Example:• This is from a DevC++ make file• Create ggFrm.oObjects/MingW/ggFrm.o: $(GLOBALDEPS)
ggFrm.cpp ggFrm.h date.h
$(CPP) -c ggFrm.cpp –o Objects/MingW/ggFrm.o $(CXXFLAGS)
Copyright © 2015 Curt Hill
Implicit Rules• Also known as inference rules• This keeps us from explicitly specifying
all the rules explicitly• Usually involve a wildcard character %• Consider the following implicit rule:
%.obj : %.cpp[tab] $(CPP) –c $(.SOURCE)
• This says: whenever you need an object file, such as x.obj, then do a gcc –c x.cpp
Copyright © 2015 Curt Hill
Directives• If statements that allow some
alternatives• The keywords are if, else, elif, endif
– Sometimes these are prefixed by a % or ! in various derivatives
• This allows us to parameterize a makefile
Copyright © 2015 Curt Hill
Example:if $(CC) == bcc LDFLAGS = /Lf:\bc\lib
elif $(CC) == cl LDFLAGS = /Lf:\c6\lib; else
abort endif
Copyright © 2015 Curt Hill
Languages• Do not be confused, the C family is not
the only language processing that can occur
• Many C/C++ projects have one or more subroutines in assembly– FORTRAN numerical routines are also
common
• Most GUIs in Windows have a source file, often a .rc, that compiles into a .res file – Wxforms compile eventually into .res
Copyright © 2015 Curt Hill
DevC++• Uses a rather normal UNIX style
make• The script is in:
makefile.win– Even in a console program
• Program itself is:…\MinGW32\bin\mingw32-make.exe
• The project file is not the make file– It looks like a UNIX initialization file
Copyright © 2015 Curt Hill
Alternatives• There is no compelling reason why a
system has to follow the UNIX pattern for a make file
• Eclipse merely compiles all Java files in the projects directory
• Visual Studio has a proprietary (and hidden) make process
• Borland/CodeGear/Embarcadero used a variant of UNIX make up through version 6 and then switched to an XML format
Copyright © 2015 Curt Hill
References• Here are some web references for
more information:• http://mrbook.org/blog/tutorials/make/• http://www.cs.colby.edu/maxwell/
courses/tutorials/maketutor/• http://www.cs.swarthmore.edu/
~newhall/unixhelp/howto_makefiles.html
• http://www.opussoftware.com/tutorial/TutMakefile.htm
Copyright © 2015 Curt Hill
Finally• We should browse through a make
file or two• Inher_demo has several classes
including an inheritance hierarchy• Projects\p2c\src\make is a standard
UNIX make
Copyright © 2015 Curt Hill