COMP 2012H

Honors OOP and Data Structures

Lab 7: Separate Compilation

Objective

The objective is to learn the separate compilation and the usage of Makefile in both Eclipse IDE and Linux command-prompt environment 

Please refer to the following link if you are not familiar with the common Linux commands: http://files.fosswire.com/2007/08/fwunixref.pdf

Walking through a Simple Example

Suppose we have the following files and we want to make a color printing program out of them: blue.h, blue.cpp, green.h, green.cpp and main.cpp.

Solution 1: put everything in one line

In the console, type:

g++ blue.cpp green.cpp main.cpp -o printcolor

It works.

• Problem 1: what if we change the content of green.cpp? Do we have to build everything again (including the files that remain intact, like blue.cpp)?
• Problem 2: what if we have another 100 colors to add to our program? Every time we add a new color, we need to build the program again until finally we have to type 100 filenames on the command line? It is messy and error-prone.

Solution 2: Separate compilation and makefile

One thing at a time:

g++ -c  blue.cpp

g++ -c  green.cpp

g++ blue.o green.o main.cpp -o printcolor

If we change green.cpp, we just need to rebuild green.o and printcolor, leaving the blue color files untouched.

Use a makefile to put everything together, thus every time we just need to type "gmake" to do compiling, assembling and linking.

About Makefile

Reference material for the Makefile:  makefile.pdf  (TA in your lab section will briefly go through the slides of the Makefile)

• It makes compilation much easier. You just need to type one simple short command instead of a long complicated ones. The purpose of the make utility is to determine automatically which pieces of a large program need to be recompiled and then issue the corresponding commands to recompile them.
• Most of the time software in Unix-like operating systems is installed using gmake/make, not by utilities like InstallShield on the Windows platform. If you encounter any problem during software installation, you will need to examine the makefile. Hence understanding how to use makefile can help you tremendously.
• To use make, you must first write a file called makefile that describes the relationships among the files in your program and includes the commands for processing the files accordingly.
• In a program, typically the executable file is updated from the object files, which are in turn created by compiling the source files.

Create and Use a g++ Makefile

You can use gmake (which calls g++) to compile and link your program or object files. When using gmake, it looks for a file called makefile or Makefile. (The name Makefile is preferred as it can easily be distinguished from other files which typically have filenames in lowercase.) You can write all the rules in your makefile to simplify and speed up your compilation and linking process.

Sample Makefile.

To make and use a g++ makefile, do the following in the console:

1.      Create a text file called Makefile

·    The simplest way is to type:

pico Makefile

               Or you can use any text editor like Vi or Emacs

2.      Edit the makefile, add:

·    Variable definitions (optional), in the form:

VARIABLE_NAME = variable_definition

               Such as:

                  TARGET = printcolor

               Use the variable by $(VARIABLE_NAME)

·    Dependencies followed by compilation rules in the second line, such as:

blue.o: blue.h blue.cpp

      $(CXX) $(CXXFLAGS) -c blue.cpp

        Which translates to, blue.o depends on blue.h and blue.cpp, compile blue.o using the rule: g++ (flags) –c blue.cpp.

        The tag all and clean specifies the final target to make, and the rules to clean up.

3.      Save and quit editing. Use the makefile by typing:

        make or make all

        and you should see the program being compiled and the target being created.

            Clean up all results by typing:

        make clean

Work on Makefile with Eclipse

• Create a Makefile project "printcolor" under Eclipse.

• Copy files to the project directory ( cspeter should be replaced by your login ID )

• Choose New > File to add a new Makefile to the current project

• Type in the content of the Makefile. Here is a sample Makefile based on the above description:

• Create a make target. Based on the rules defined on the Makefile, the target name should be equal to all

• Build the project by clicking the hammer button
  • You may receive some unknown warning messages. It should be fine if the executable named printcolor is generated (can be viewed from the Project Explorer on the left panel)
  • You should notice that Makefile enables the separate compilation
  • Parameters
    • -Wall means show all warning messages when compiling a cpp file
    • OBJS stores all the intermediate object files generated during the compilation process
    • LIBS stores external libraries. We don’t require external libraries, so we omit this variable
    • TARGET is the name of the final executable

• Run the executable printcolor

Lab Task

Download

• date_all.cpp contains the definition and implementation of the class Date as well as the main function

Lab Work

Declaration, Definition and Implementation

In practice, programmers always separate a segment of program source code into three parts: declaration, definition and implementation. The purpose is to separate the interface from the actual implementation to make the program easier to understand and reuse.  The objectives are to achieve:

• Clean and concise header files (*.h)
• Separate the compilation process to avoid unnecessary recompilation (or to achieve minimum recompilation) when some of the program files are changed

For example, consider the class

class Date;

Class declaration: Introduce a class called Date to the compiler, but with only function prototypes without any detailed information provided yet

class Date {

   Date();

   // ... function prototypes and member variables

};

Class definition or implementation: Define the class Date's member variables and member functions so that codes can be generated.  The are in the form of the following

Date::Date() {

   // ... detailed implementation

};

// ...

Part I:

1. Re-factor the program in date_all.cpp to make use of the idea of separate compilation, which is to separate the class Date's definition and implementation in the given date_all.cpp:
   • Put the class Date's definition into date.h
   • Put the class Date's implementation into date.cpp
   • Put the main function into main.cpp
2. Complete the code according to comment TODO
3. Create a g++ Makefile so that it can:
   • Compile date.cpp to generate an object file date.o
   • Compile main.cpp to generate an object file main.o
   • Remove all .o and executable files in clean target
   • Link the object files and generate the executable code with filename lab7

Part II: (Optional)

1. In Eclipse, create a Makefile project called "date".
2. Copy the re-factored source and header files (date.h, date.cpp, main.cpp) to the project.
3. Complete the Makefile created by Eclipse, so that it can do the same thing as the g++ Makefile created in Part I.

References

• An introduction to Makefile
• Another easy page
• Makefile tutorial
• For more information of g++, please see the reference g++ command line arguments.

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