Laboratory Exercises, C++ Programming

12 Tools for Practical C++ Development
ltest.o: ltest.cc list.h
On the line following the dependency specification you write a shell command that generates the
target. This is called an explicit rule. Example (with a short command line without options):
ltest.o: ltest.cc list.h
g++ -c ltest.cc
Make has a very unusual syntax requirement: the shell command must be preceded by a tab
character; spaces are not accepted.
An implicit rule does not give an explicit command to generate the target. Instead, it relies
on make’s large collection of default rules. For instance, make knows how to generate .o-files
from most kinds of source files, for instance that g++ is used to generate .o-files from .cc-files.
The actual implicit rule is:
$(CXX) $(CPPFLAGS) $(CXXFLAGS) -c -o $@ $<
CXX, CPPFLAGS, and CXXFLAGS are variables that the user can define. The syntax $(VARIABLE) is
used to evaluate a variable, returning its value. CXX is the name of the C++ compiler, CPPFLAGS
are the options to the preprocessor, CXXFLAGS are the options to the compiler. $@ expands to the
name of the target, $< expands to the first of the prerequisites.
We are now ready to write our first makefile, which will build the ltest program from lab 1.
The value g++ for CXX is default, thus that definition is optional. CPPFLAGS and CXXFLAGS are
empty by default. CXXFLAGS is almost always redefined.
# Compiler and compiler options:
CXX = g++
CXXFLAGS = -pipe -O2 -Wall -W -ansi -pedantic-errors
CXXFLAGS += -Wmissing-braces -Wparentheses -Wold-style-cast
# Linking:
ltest: ltest.o list.o
$(CXX) -o $@ $^
# Dependencies, the implicit rule .cc => .o is used:
ltest.o: ltest.cc list.h
list.o: list.cc list.h
$^ expands to the complete list of prerequisites. We will make improvements to this makefile
later.
Suppose that none of the files ltest, ltest.o, list.o exists. Then, the following commands are
executed when you run make (the long command lines have been wrapped):
make ltest
g++ -pipe -O2 -Wall -W -ansi -pedantic-errors -Wmissing-braces -Wparentheses
-Wold-style-cast -c -o ltest.o ltest.cc
g++ -pipe -O2 -Wall -W -ansi -pedantic-errors -Wmissing-braces -Wparentheses
-Wold-style-cast -c -o list.o list.cc
g++ -o ltest ltest.o list.o
If an error occurs in one of the commands, make will be aborted. If there, for instance, is an error
in list.cc, the compilation of that file will be aborted and the program will not be linked. When
you have corrected the error and run make again, it will discover that ltest.o is up to date and
only remake list.o and ltest.
If you run make without a target name as parameter, make builds the first target it finds in the