CS 228 unit -*- Outline -*-

* compiling C++ programs (DD 1.12-13, 1.14-16)

** compilers vs. interpreters
	to explain purpose of a compiler
-------------------------------
    COMPILERS vs. INTERPRETERS


  (Scheme program)  -----------> output
                    interpreter


  {C++ program}
       |
       | compiler
       |
       v
   [exectuable]      ----------> output
                       machine
-------------------------------
	Some interpreters (e.g. Chez Scheme)
		work by quickly compiling what you type then running it.
	But the general idea of an interpreter is that it is a high-level
		machine.

** phases of compilation (DD fig 1.1)
	The above suppresses the details of preprocessing and linking
	On Unix, g++ does preprocessing, compilation and linking

*** preprocessing and compiling
------------------------------
  IMPORTANT PHASES OF COMPILATION

% g++ -ansi -pedantic -Wall prog.C


     {prog.C}
        |
	| preprocessor
	|
	v
     {prog.C with #include files
               and macros expanded}
	|
	| compiler proper
	|
	v
     [a.out]

% ./a.out
Welcome to the world of compilation!
--------------------------------
	there is also an assembly phase not shown, and probably others

	The -ansi and -pedantic flag turn off extensions to standard C++
	The -Wall flag asks for all warnings.

	the compiler does the preprocessing invisibly
		to see how preprocessing works, use -E option and look
		at the prog.ii file which is created.

	Q: what would change if the program was named myprog.C?

	To get a different output file name, use the -o flag

--------------------------------
% g++ -ansi -pedantic -Wall \
          -o prog.exe prog.C
% ./prog.exe
Welcome to the world of compilation!
--------------------------------
	
-------------------------
    SHELL SCRIPT FOR CALLING g++

The command
   /home/cs228/public/bin/ansicpp
can be used instead of
  g++ -ansi -pedantic -Wall
--------------------------
	it does the same thing.
	% which ansicpp
--------------------------
% ansicpp -o prog.exe prog.C
% ./prog.exe
--------------------------
	Show the code for prog.C

	Q: what would change if the program was named myprog.C?

** linking
	to demonstrate input, header files, and linking
-----------------------------
        PROBLEM

Write a program to input a number
and output its cosine.
------------------------------

	be sure to explain everything as go along,
		but don't get bogged down in the C++

SNAPSHOT 1

// cosine-main.C

int main()
  // MODIFIES: cin, cout
  // POST: cout has a prompt written to it,
  // cin has a number read from it, and
  // cout has the cosine of that number added to it.
{
  // prompt for input
  // read num
  // write cosine of num
}

////////////// for doing cosine, use man to find it, could also use book

SNAPSHOT 2

// cosine-main.C

int main()
  // MODIFIES: cin, cout
  // POST: cout has a prompt written to it,
  // cin has a number read from it, and
  // cout has the cosine of that number added to it.
{
  prompt("Number? ");

  // read num
  double num;
  cin >> num;

  // write cosine of num
  cout << cos(num) << endl;
}

////////// try compiling this.  Show the errors.
	need to have a declaration for prompt, and for cin, cout, and endl.
	#include <iostream.h> to get declarations for the io stuff
	give our own declaration of prompt

	Briefly explain the declaration concept:
		each name has a type, compiler has to know types of functions
		(like prompt) and variables (like cin) before they are used.


SNAPSHOT 3
// cosine-main.C

#include <iostream.h>
extern void prompt(char *promptstring);

int main()
  // MODIFIES: cin, cout
  // POST: cout has a prompt written to it,
  // cin has a number read from it, and
  // cout has the cosine of that number added to it.
{
  prompt("Number? ");

  // read num
  double num;
  cin >> num;

  // write cosine of num
  cout << cos(num) << endl;
}

////////////// now get undefined symbol errors: cos and prompt.
	but we also need a declaration for cos, and need to write prompt.

SNAPSHOT 4
// cosine-main.C

#include <iostream.h>
#include <math.h>
extern void prompt(char *promptstring);

int main()
  // MODIFIES: cin, cout
  // POST: cout has a prompt written to it,
  // cin has a number read from it, and
  // cout has the cosine of that number added to it.
{
  prompt("Number? ");

  // read num
  double num;
  cin >> num;

  // write cosine of num
  cout << cos(num) << endl;
}

void prompt(char *promptstring)
  // MODIFIES: cout
  // POST: promptstring has been added to cout.
{
  cout << promptstring;
}


///////////// now just need to link with -lm flag to get cosine.

----------------------------
    HEADER FILES and LINKING
        SUMMARY

% ansicpp -o cosine.exe cosine-main.C -lm

  /usr/local/lib/g++-include/iostream.h
                             math.h
  {cosine-main.C}
        |
	| preprocessor
	|
	v
  {cosine-main.C
            with iostream.h and math.h}
	|
	| compiler proper
	|
        v
  {object file} and /usr/local/lib/libm.a
        |
        | linking loader
        |
	v
  [cosine.exe]  ---------> output
                machine

% ./cosine.exe
Number? 3.14159
-1
----------------------------
	point out connection between -lm and libm.a

	Q: questions about this?

** separate compilation (if time)
	If you have a useful function like prompt


SNAPSHOT 5
// cosine-main.C

#include <iostream.h>
#include <math.h>
extern void prompt(char *promptstring);

int main()
  // MODIFIES: cin, cout
  // POST: cout has a prompt written to it,
  // cin has a number read from it, and
  // cout has the cosine of that number added to it.
{
  prompt("Number? ");

  // read num
  double num;
  cin >> num;

  // write cosine of num
  cout << cos(num) << endl;
}

// prompt.C

#include <iostream.h>

void prompt(char *promptstring)
  // MODIFIES: cout
  // POST: promptstring has been added to cout.
{
  cout << promptstring;
}


///////	compile with
	ansicpp -o cosine.exe prompt.C cosine-main.C -lm

	and with
	ansicpp -c prompt.C
	ansicpp -c cosine-main.C
	ansicpp -o cosine.exe prompt.o cosine-main.o -lm

	Why do this, so can change cosine-main without recompiling prompt.
	Edit it to have it print "The cosine of " << num << " is ".

** making own header file
	make prompt.h, put specs in it,
	and include it in cosine-main.C and in prompt.C
		(include it there so catch errors earlier).

-----------------------------------
  SEPARATE COMPILATION SUMMARY

% ansicpp -c cosine-main.C

  /usr/local/lib/g++-include/iostream.h
                             math.h
  ./prompt.h
  {cosine-main.C}
        |
	| preprocessor
	|
	v
  {cosine-main.C with iostream.h, math.h
                 and prompt.h}
	|
	| compiler proper
	|
        v
   cosine-main.o


% ansicpp -o cosine.exe prompt.o \
                        cosine-main.o -lm

  prompt.o, cosine-main.o 
                and /usr/local/lib/libm.a
        |
        | linking loader
        |
	v
  [cosine.exe]  ---------> output
                machine
-----------------------------------

	Q: what if our program also involved graphics.C and graphics.h?

** for more info
	see $PUB/doc/running-c++.txt, man page for g++

	we'll save makefiles for later