OSU CSE 2421
There’s a good demo at:
Likely, one of the best 15 minutes you will spend this semester (on coursework).
GNU Makefile manual: https://www.gnu.org/software/make/manual/make.html For your reference
J.E.Jones
OSU CSE 2421
make is a utility for building and maintaining groups of programs (and other types of files) from source code
The purpose of the make utility is to determine automatically which pieces of a large program need to be re-compiled and issue the commands necessary to recompile them.
To use make, you must create a file call Makefile (or makefile)that describes the relationships among files in your program
make decides whether a target needs to be regenerated by comparing file modification times
J. E. Jones
OSU CSE 2421
make is a Unix/linux utility, which is used to manage building (compilation) of programs, but it can do other things, too.
It is very commonly used in industry in Unix/linux environments.
For a large program, it is more efficient for the developer and the machine if the program is written as a number of smaller files; recompiling each of these various files that make up the program is only done when something changes which requires recompilation.
This also promotes reusability of code, because source code for functions can be kept in separate files, and the file can be called and compiled in any program for which it is useful.
Makefiles contain file dependency lists and UNIX commands and will run them in a specified sequence.
Anything that can be entered at the UNIX/linux command prompt can be in the Makefile.
J. E. Jones
OSU CSE 2421
The name of your Makefile has to be: Makefile or makefile in this class (which are the two default options)
The directory you put the Makefile in matters!
You can only have one Makefile per directory.
Asimplemakefileconsistsof“rules”withthefollowingformat:
target: dependencies … Unix/linux commands… …
…
where
target is usually the name of a file that is generated by a program; examples of targets are executable or object files. A target can also be the name of an action to carry out, such as ‘clean’. We are creating a .zip target in our Makefiles.
dependency is a file that is used as input to create the target. A target often depends on several files. Thus “dependencies” above.
Unix/linux command is an action that make carries out. More than one command, either on the same line or each on its own line can be listed
Note: you need to put a tab character at the beginning of every command line!
J. E. Jones
OSU CSE 2421
MAKEFILES ARE UNFORGIVING WHEN IT COMES TO WHITESPACE!
To run make… you must be in the directory where the file Makefile is.
make is a Unix/linux utility program
Makefiles can only accept single line comments and they start with
a#
The command to run make on the Makefile file in a directory:
% make target Or
% make
Note: target is also called section name or tag-name, if no target is referenced, the first target in the Makefile is used.
J. E. Jones
OSU CSE 2421
Let’s look at a program with multiple source files that could be built with make. Let’s suppose we want the executable to be called mkprog
/* mkfunc.h */
/* mkfact.c */
/* The header file contains function prototypes for all functions in the program, except main() and library functions
#include “mkfunc.h”
/* ” ”, not < > because it’s a local file */
*/
int fact(int n) { if (n != 1) {
void print_hello(); int fact(int n);
return (n * fact(n – 1)); }
else return 1; }
J. E. Jones
OSU CSE 2421
/* mkhello.c */
/* mkmain.c */
#include “mkfunc.h” #include
#include “mkfunc.h” #include
void print_hello() { printf(“Hello World!\n”);
int main() {
print_hello();
printf(“5 factorial is %d”, fact(5)); return 0;
}
}
J. E. Jones
OSU CSE 2421
Compiling our example from the command line would look like:
gcc -ansi -pedantic -o mkprog mkmain.c mkhello.c mkfact.c
The more files needed to create an executable module (e.g. mkprog), the more likely it is that we will “fat finger” the command.
The history feature of the bash shell, helps this some, but what if we haven’t compiled the program in the last 20 commands?
“all” should be the default target for a makefile % make all
The make utility will execute this target, “all”, by default, if no other one is specified, so the following command has the same effect:
% make /* target “all” is implied */
Using the –c option with gcc means that compilation of the specified file will stop when the .o file of the same name has been created (for example, gcc –c test.c creates test.o). No linking with other .o files is done.
J. E. Jones
OSU CSE 2421
# This is a Makefile for an executable called mkprog # mkprog is comprised of three .c files and one .h file
all: mkprog # we are creating mkprog with this makefile
#target mkprog must be re-created if mkmain.o, mkfact.o, or mkhello.o change mkprog: mkmain.o mkfact.o mkhello.o #mkprog needs 3 .o files
gcc mkmain.o mkfact.o mkhello.o -o mkprog #command to create mkprog #mkmain.o must be re-created if mkmain.c or mkfunc.h change
mkmain.o: mkmain.c mkfunc.h
gcc –ansi –pedantic –c mkmain.c # this command creates mkmain.o #mkfact.o must be re-created if mkfact.c or mkfunc.h change
mkfact.o: mkfact.c mkfunc.h
gcc –ansi –pedantic –c mkfact.c # this command creates mkfact.o #mkhello.o must be re-created if mkhello.c or mkfunc.h change
mkhello.o: mkhello.c mkfunc.h
gcc –ansi –pedantic –c mkhello.c # this command creates mkhello.o #clean is another target. It removes all created dependency files so that
#all files are forced to recompile
clean:
rm –rf *.o mkprog
J. E. Jones
OSU CSE 2421
# This is a Makefile for an executable called mkprog # mkprog is comprised of three .c files and one .h file
Must use a tab here NO spaces!
all: mkprog # we are creating mkprog with this makefile
#target mkprog must be re-created if mkmain.o, mkfact.o, or mkhello.o change mkprog: mkmain.o mkfact.o mkhello.o #mkprog needs 3 .o files
gcc mkmain.o mkfact.o mkhello.o -o mkprog #command to create mkprog #mkmain.o must be re-created if mkmain.c or mkfunc.h change
mkmain.o: mkmain.c mkfunc.h
gcc –ansi –pedantic –c mkmain.c # this command creates mkmain.o #mkfact.o must be re-created if mkfact.c or mkfunc.h change
mkfact.o: mkfact.c mkfunc.h
gcc –ansi –pedantic –c mkfact.c # this command creates mkfact.o #mkhello.o must be re-created if mkhello.c or mkfunc.h change
mkhello.o: mkhello.c mkfunc.h
gcc –ansi –pedantic –c mkhello.c # this command creates mkhello.o #clean is another target. It removes all created dependency files so that
#all files are forced to recompile
clean:
rm –rf *.o mkprog
J. E. Jones
OSU CSE 2421
# This is a Makefile for an executable called mkprog # mkprog is comprised of four .c files and one .h file
all: mkprog
mkprog: mkmain.o mkfact.o mkhello.o mk_newfunc.o
gcc mkmain.o mkfact.o mkhello.o mk_newfunc.o -o mkprog mkmain.o: mkmain.c mkfunc.h
gcc –ansi –pedantic –c mkmain.c
mkfact.o: mkfact.c mkfunc.h
gcc –ansi –pedantic –c mkfact.c
mkhello.o: mkhello.c mkfunc.h
gcc –ansi –pedantic –c mkhello.c
mk_newfunc.o: mk_newfunc.c mkfunc.h
gcc –ansi –pedantic –c mk_newfunc.c
clean:
rm –rf *.o mkprog
J. E. Jones
OSU CSE 2421
Based on the makefile above, make will create a dependency table:
mkmain.o mkmain.c mkfunc.h
mkfact.o mkfact.c mkfunc.h
mkhello.o mkhello.c mkfunc.h
mkprog
*Using this table, make can determine what to recompile based on changes in any of the files.
J. E. Jones
OSU CSE 2421
% make clean
rm –rf *.o mkprog
% make
gcc -ansi -pedantic -c mkmain.c
gcc -ansi -pedantic -c mkfact.c
gcc -ansi -pedantic -c mkhello.c
gcc mkmain.o mkfact.o mkhello.o -o mkprog % mkprog
Hello World!
5 factorial is 120
% make
make: Nothing to be done for ‘all’.
J. E. Jones
OSU CSE 2421
# comments in a Makefile start with sharp
# target all means all targets currently defined in this file
# we have 3 separate targets in this Makefile, our zip file and 2 executables all: lab2.zip bit_decode1 bit_decode2
# this target is the .zip file that must be submitted to Carmen
# if the dependencies (Makefile, bit_encode.c or LAB2README) change, a new zip file is created.
lab2.zip: Makefile bit_decode.c LAB2README
zip lab2.zip Makefile bit_decode.c LAB2README
# this target is the bit decryption executable that doesn’t prompt for input bit_decode1: bit_decode1.o
gcc bit_decode1.o -o bit_decode1
# this target is the dependency for bit_decode1
# we use “-o bit_decode1.o” here so that the .o file doesn’t have the same name as the .c file # most of the time we can use the default .o file, but since in this instance we are creating # two separate .o files using the same .c file, we must specify a name for the .o file bit_decode1.o: bit_decode.c
gcc -ansi -pedantic -g -c -o bit_decode1.o bit_decode.c
J. E. Jones
OSU CSE 2421
# this target is the bit decryption executable that prompts for input from the keyboard
bit_decode2: bit_decode2.o
gcc bit_decode2.o -o bit_decode2
# this target is the dependency for bit_decode2
# we use “-o bit_decode2.o” here so that the .o file doesn’t
# have the same name as the .c file
# note that this compile includes “-D PROMPT” so that our code # where we use ifdef’s gets included
bit_decode2.o: bit_decode.c
gcc -ansi -pedantic -D PROMPT -g -c -o bit_decode2.o bit_decode.c
# this target deletes all files produced from the Makefile
# so that a completely new compile of all items is required clean:
rm -rf *.o bit_decode1 bit_decode2 lab2.zip
J. E. Jones
OSU CSE 2421
# comments in a Makefile start with sharp
# target all means all targets currently defined in this file
# we have 3 separate targets in this Makefile, our zip file and 2 executables all: lab2.zip bit_decode1 bit_decode2 bit_encode
# this target is the .zip file that must be submitted to Carmen
# if the dependencies (Makefile, bit_encode.c or LAB2README) change, a new zip file is created.
lab2.zip: Makefile bit_decode.c LAB2README bit_encode.c
zip lab2.zip Makefile bit_decode.c LAB2README bit_encode.c
# this target is the bit decryption executable that doesn’t prompt for input bit_decode1: bit_decode1.o
gcc bit_decode1.o -o bit_decode1
# this target is the dependency for bit_decode1
# we use “-o bit_decode1.o” here so that the .o file doesn’t have the same name as the .c file # most of the time we can use the default .o file, but since in this instance we are creating # two separate .o files using the same .c file, we must specify a name for the .o file bit_decode1.o: bit_decode.c
gcc -ansi -pedantic -g -c -o bit_decode1.o bit_decode.c
J. E. Jones
OSU CSE 2421
# this target is the bit decryption executable that prompts for input from the keyboard bit_decode2: bit_decode2.o
gcc bit_decode2.o -o bit_decode2
# this target is the dependency for bit_decode2
# we use “-o bit_decode2.o” here so that the .o file doesn’t
# have the same name as the .c file
# note that this compile includes “-D PROMPT” so that our code # where we use ifdef’s gets included
bit_decode2.o: bit_decode.c
gcc -ansi -pedantic -D PROMPT -g -c -o bit_decode2.o bit_decode.c
# this target is the encode program bit_encode: bit_encode.o
gcc bit_encode.o -o bit_encode
# this target is the dependency for bit_encode.o bit_encode.o: bit_encode.c
Notice we are using the default .o file here No –o option listed.
gcc -ansi -pedantic -g -c bit_encode.c
# this target deletes all files produced from the Makefile
# so that a completely new compile of all items is required clean:
rm -rf *.o bit_decode1 bit_decode2 bit_encode lab2.zip
J. E. Jones