Make - Revision history

GethinWilliams: /* Key Concepts: Rules, Targets and Dependencies */

2013-02-14T16:50:45Z

Key Concepts: Rules, Targets and Dependencies

GethinWilliams: /* Key Concepts: Rules, Targets and Dependencies */

2013-02-14T16:48:09Z

Key Concepts: Rules, Targets and Dependencies

GethinWilliams: /* Key Concepts: Rules, Targets and Dependencies */

2013-02-14T16:44:37Z

Key Concepts: Rules, Targets and Dependencies

GethinWilliams at 17:04, 7 March 2011

2011-03-07T17:04:36Z

Show changes

GethinWilliams: /* Key Concepts: Rules, Targets and Dependencies */

2011-03-07T16:59:14Z

Key Concepts: Rules, Targets and Dependencies

GethinWilliams: /* Key Concepts: Rules, Targets and Dependencies */

2011-03-07T16:34:36Z

Key Concepts: Rules, Targets and Dependencies

GethinWilliams: /* Key Concepts: Rules, Targets and Dependencies */

2011-03-07T16:34:11Z

Key Concepts: Rules, Targets and Dependencies

GethinWilliams: /* Key Concepts: Rules, Targets and Dependencies */

2011-03-07T16:32:51Z

Key Concepts: Rules, Targets and Dependencies

GethinWilliams at 16:01, 5 July 2010

2010-07-05T16:01:13Z

GethinWilliams: /* Fortran90 Modules: Ordering and Dependencies */

2009-02-04T17:25:22Z

Fortran90 Modules: Ordering and Dependencies

← Older revision		Revision as of 16:50, 14 February 2013
Line 99:		Line 99:

	Before we leave this example, there are two more rules to look at—the '''clean''' and '''spotless''' rules. These tidy up any files we created using the makefile. It is good practice, and rather handy, to write these rules. They both have the questionable distinction of being designated '''PHONY'''. This indicates that the targets do not refer to a real file. Since these rules are not part of any chain, we must call them explicitly by name to trigger them, i.e. '''make clean''', or '''make spotless'''. They have no dependencies and the targets don’t exist, so the actions will always be triggered.		Before we leave this example, there are two more rules to look at—the '''clean''' and '''spotless''' rules. These tidy up any files we created using the makefile. It is good practice, and rather handy, to write these rules. They both have the questionable distinction of being designated '''PHONY'''. This indicates that the targets do not refer to a real file. Since these rules are not part of any chain, we must call them explicitly by name to trigger them, i.e. '''make clean''', or '''make spotless'''. They have no dependencies and the targets don’t exist, so the actions will always be triggered.
		+
		+	Note that if you type '''make clean''' (.o files deleted) and then '''make''' again, the source code will be recompiled, despite the presence of a valid executable. Make will ensure that the whole chain of dependencies is intact.

	=More Files, I Say, More Files!=		=More Files, I Say, More Files!=

@@ Line 96: / Line 96: @@
 [[Image:Chain.jpg|frame|center|Schematic chaining of make rules]]
-For our simple makefile, the 'all' rule is first.  The dependency is unsatisfied, but there is a rule with '''hello_world.o''' as a target.  The dependency on this second rule is satisfied (the file hello_world.c exists).  The associated action is performed, and hello_world.o is created.  Winding back up the chain, the ‘all’ rule can now trigger, and '''hello_world.exe''' is created.  Hurrah!
+For our simple makefile, the 'all' rule is first.  The dependency is unsatisfied, but there is a rule with '''hello_world.exe''' as a target.  The dependency on this second rule (hello_world.o) is also missing, but the dependency on the thrid rule is satisfied (the file hello_world.c exists).  The associated action is performed, and hello_world.o is created.  Winding back up the chain, the other rules can now also trigger '''hello_world.exe''' is created.  Hurrah!
 Before we leave this example, there are two more rules to look at—the '''clean''' and '''spotless''' rules.  These tidy up any files we created using the makefile.  It is good practice, and rather handy, to write these rules.  They both have the questionable distinction of being designated '''PHONY'''.  This indicates that the targets do not refer to a real file.  Since these rules are not part of any chain, we must call them explicitly by name to trigger them, i.e. '''make clean''', or '''make spotless'''.  They have no dependencies and the targets don’t exist, so the actions will always be triggered.

@@ Line 78: / Line 78: @@
 <source lang="make">
-all : hello_world.o
+hello_world.exe : hello_world.o
 	gcc hello_world.o –o hello_world.exe
 </source>
-In this rule, however, there isn't—and never will be—a file called '''all'''.  When this is the case, the rule will always trigger, should the dependencies be satisfied.  (Try typing '''make''' a few times.)
+Lastly, but not least we have:
-OK, how to make read a makefile?
+<source lang="make">
 When calling make in its default mode, it will look for a file called Makefile (or makefile) in the current directory and start reading it from the top down.  It will read down until it finds the first rule and look to see if the dependencies are satisfied.  If the dependencies are not satisfied, it will look for a rule, with a target matching the missing dependency, and so on.  In this way, make '''chains''' down a sequence of rules until it finds a satisfied dependency and then will wind back up to its starting point, performing all the specified actions along the way.
@@ Line 92: / Line 98: @@
 For our simple makefile, the 'all' rule is first.  The dependency is unsatisfied, but there is a rule with '''hello_world.o''' as a target.  The dependency on this second rule is satisfied (the file hello_world.c exists).  The associated action is performed, and hello_world.o is created.  Winding back up the chain, the ‘all’ rule can now trigger, and '''hello_world.exe''' is created.  Hurrah!
-Before we leave this example, there are two more rules to look at—the '''clean''' and '''spotless''' rules.  These tidy up any files we created using the makefile.  It is good practice, and rather handy, to write these rules.  They both have the questionable distinction of being designated '''PHONY'''.  This indicates that the targets do not refer to a real file.  Since these rules are not part of any chain, we must call them explicitly by name to trigger them, i.e. '''make clean''', or '''make spotless'''.  They have no dependencies and the targets don’t exist, so the actions will always be triggered.  (We could, and-strictly speaking-should, have declared the 'all' rule as PHONY too.  It kept things simpler up until now, and there was no file called 'all' to mess things up.)
+Before we leave this example, there are two more rules to look at—the '''clean''' and '''spotless''' rules.  These tidy up any files we created using the makefile.  It is good practice, and rather handy, to write these rules.  They both have the questionable distinction of being designated '''PHONY'''.  This indicates that the targets do not refer to a real file.  Since these rules are not part of any chain, we must call them explicitly by name to trigger them, i.e. '''make clean''', or '''make spotless'''.  They have no dependencies and the targets don’t exist, so the actions will always be triggered.
 =More Files, I Say, More Files!=

@@ Line 68: / Line 68: @@
 A rule will trigger if the dependencies are satisfied and they are ‘newer’ than the target.  If the rule is triggered, the actions will be performed.  This all sounds rather abstract, so let’s consider something more concrete.  Take a look at the contents of Makefile in our example.  In particular, the rule:
-<pre>
+<source lang="make">
 hello_world.o : hello_world.c
 	gcc –c hello_world.c –o hello_world.o
-</pre>
+</source>
 So, our target here is '''hello_world.o''', our dependency is '''hello_world.c''' and our action is to use gcc to create an object file from the source code.  Our dependency is satisfied, since the file hello_world.c exists.  The file hello_world.o does not exist.  In this case the rule will trigger and compilation action will be performed.  If the file hello_world.o did exist, make would compare the date-stamps on the files hello_world.o and hello_world.c.  If the source code proved to be newer than object code, the file hello_world.o would be updated using the specified action, i.e. gcc would be invoked again.
@@ Line 77: / Line 77: @@
 We see a similar pattern in the rule:
-<pre>
+<source lang="make">
 all : hello_world.o
 	gcc hello_world.o –o hello_world.exe
-</pre>
+</source>
 In this rule, however, there isn't—and never will be—a file called '''all'''.  When this is the case, the rule will always trigger, should the dependencies be satisfied.  (Try typing '''make''' a few times.)

@@ Line 55: / Line 55: @@
 Makefiles are composed of rules and variables.  We'll see some variables soon.  For now, let’s just look at some rules.  A rule in a makefile has the general form:
-<source lang="Makefile">
+<source lang="make">
 Target : dependencies
 	Action1

@@ Line 7: / Line 7: @@
 <pre>
-svn co http://source.ggy.bris.ac.uk/subversion-open/make/trunk make
+svn co https://svn.ggy.bris.ac.uk/subversion-open/make/trunk make
 </pre>

@@ Line 281: / Line 281: @@
 <pre>
 utils.o : utils.f90 constants.f90
 </pre>