(make.info.gz) make Deduces
Info Catalog
(make.info.gz) Variables Simplify
(make.info.gz) Introduction
(make.info.gz) Combine By Prerequisite
2.5 Letting `make' Deduce the Commands
======================================
It is not necessary to spell out the commands for compiling the
individual C source files, because `make' can figure them out: it has an
"implicit rule" for updating a `.o' file from a correspondingly named
`.c' file using a `cc -c' command. For example, it will use the
command `cc -c main.c -o main.o' to compile `main.c' into `main.o'. We
can therefore omit the commands from the rules for the object files.
Using Implicit Rules Implicit Rules.
When a `.c' file is used automatically in this way, it is also
automatically added to the list of prerequisites. We can therefore omit
the `.c' files from the prerequisites, provided we omit the commands.
Here is the entire example, with both of these changes, and a
variable `objects' as suggested above:
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 : defs.h
kbd.o : defs.h command.h
command.o : defs.h command.h
display.o : defs.h buffer.h
insert.o : defs.h buffer.h
search.o : defs.h buffer.h
files.o : defs.h buffer.h command.h
utils.o : defs.h
.PHONY : clean
clean :
rm edit $(objects)
This is how we would write the makefile in actual practice. (The
complications associated with `clean' are described elsewhere. See
Phony Targets, and Errors in Commands Errors.)
Because implicit rules are so convenient, they are important. You
will see them used frequently.
Info Catalog
(make.info.gz) Variables Simplify
(make.info.gz) Introduction
(make.info.gz) Combine By Prerequisite
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