From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/gnu_make/variables-simplify.html | 38 ++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) create mode 100644 devdocs/gnu_make/variables-simplify.html (limited to 'devdocs/gnu_make/variables-simplify.html') diff --git a/devdocs/gnu_make/variables-simplify.html b/devdocs/gnu_make/variables-simplify.html new file mode 100644 index 00000000..7ccc54c5 --- /dev/null +++ b/devdocs/gnu_make/variables-simplify.html @@ -0,0 +1,38 @@ +

Variables Make Makefiles Simpler

In our example, we had to list all the object files twice in the rule for edit (repeated here): 

edit : main.o kbd.o command.o display.o \
+              insert.o search.o files.o utils.o
+        cc -o edit main.o kbd.o command.o display.o \
+                   insert.o search.o files.o utils.o
+
+

Such duplication is error-prone; if a new object file is added to the system, we might add it to one list and forget the other. We can eliminate the risk and simplify the makefile by using a variable. Variables allow a text string to be defined once and substituted in multiple places later (see How to Use Variables).

It is standard practice for every makefile to have a variable named objects, OBJECTS, objs, OBJS, obj, or OBJ which is a list of all object file names. We would define such a variable objects with a line like this in the makefile: 

objects = main.o kbd.o command.o display.o \
+          insert.o search.o files.o utils.o
+
+

Then, each place we want to put a list of the object file names, we can substitute the variable’s value by writing ‘$(objects)’ (see How to Use Variables).

Here is how the complete simple makefile looks when you use a variable for the object files: 

objects = main.o kbd.o command.o display.o \
+          insert.o search.o files.o utils.o
+
+edit : $(objects)
+        cc -o edit $(objects)
+main.o : main.c defs.h
+        cc -c main.c
+kbd.o : kbd.c defs.h command.h
+        cc -c kbd.c
+command.o : command.c defs.h command.h
+        cc -c command.c
+display.o : display.c defs.h buffer.h
+        cc -c display.c
+insert.o : insert.c defs.h buffer.h
+        cc -c insert.c
+search.o : search.c defs.h buffer.h
+        cc -c search.c
+files.o : files.c defs.h buffer.h command.h
+        cc -c files.c
+utils.o : utils.c defs.h
+        cc -c utils.c
+clean :
+        rm edit $(objects)
+
+
+

+ Copyright © 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022 Free Software Foundation, Inc.
Licensed under the GNU Free Documentation License.
+ https://www.gnu.org/software/make/manual/html_node/Variables-Simplify.html +

+
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