Cpp tutorial

 This tutorial offers several things.
 You’ll see some neat features of the language.
 You’ll learn the right things to google.
 You’ll find a list of useful books and web pages.
 But don’t expect too much!
 It’s complicated, and you’ll learn by doing.
 But I’ll give it my best shot, okay?

 Basic syntax
 Compiling your program
 Argument passing
 Dynamic memory
 Object-oriented programming

#include <iostream>
using namespace std;
float c(float x) {
return x*x*x;
}
int main() {
float x;
cin >> x;
cout << c(x) << endl;
return 0;
}
 Includes function definitions
for
console input and output.
 Function declaration.
 Function definition.
 Program starts here.
 Local variable declaration.
 Console input.
 Console output.
 Exit main function.

// This is main.cc
#include <iostream>
#include “mymath.h”
int main() {
// ...stuff...
}
// This is mymath.h
#ifndef MYMATH
#define MYMATH
float c(float x);
float d(float x);
#endif
Functions are declared in mymat h. h, but not defined.
They are implemented separately in mymat h. cc.

main.cc mymath.cc mydraw.cc
g++ -c main.cc g++ -c mymath.cc g++ -c mydraw.cc
↓ ↓ ↓
↓ ↓ ↓
↓ ↓ ↓
g++ -o myprogram main.o mathstuff.o drawstuff.o
main.o mymath.o mydraw.o
↓
myprogram →

// This is main.cc
#include <GL/glut.h>
#include <iostream>
int main() {
cout << “Hello!” << endl;
glVertex3d(1,2,3);
return 0;
}
 Include OpenGL functions.
 Include standard IO
functions.
 Long and tedious
explanation.
 Calls function from standard
IO.
 Calls function from OpenGL.
 Make object file.
 Make executable, link GLUT.
 Execute program.
% g++ -c main.cc
% g++ -o myprogram –lglut main.o
% ./myprogram

 Software engineering reasons.
 Separate interface from implementation.
 Promote modularity.
 The headers are a contract.
 Technical reasons.
 Only rebuild object files for modified source files.
 This is much more efficient for huge programs.

INCFLAGS =
-
I/afs/csail/group/graphics/courses/6.837/public/includ
e
LINKFLAGS =
-L/afs/csail/group/graphics/courses/6.837/public/lib
-lglut -lvl
CFLAGS = -g -Wall -ansi
CC = g++
SRCS = main.cc parse.cc curve.cc surf.cc camera.cc
OBJS = $(SRCS:.cc=.o)
PROG = a1
all: $(SRCS) $(PROG)
$(PROG): $(OBJS)
$(CC) $(CFLAGS) $(OBJS) -o $@ $(LINKFLAGS)
.cc.o:
$(CC) $(CFLAGS) $< -c -o $@ $(INCFLAGS)
depend:
makedepend $(INCFLAGS) -Y $(SRCS)
clean:
rm $(OBJS) $(PROG)
main.o: parse.h curve.h tuple.h
# ... LOTS MORE ...
Most assignments include
makef i l es, which describe
the files, dependencies, and
steps for compilation.
You can just type make.
So you don’t have to know
the stuff from the past few
slides.
But it’s nice to know.

#include <iostream>
int main() {
int n;
cin >> n;
float f[n];
for (int i=0; i<n; i++)
f[i] = i;
return 0;
}
Arrays must have known
sizes at compile time.
This doesn’t compile.

#include <iostream>
int main() {
int n;
cin >> n;
float *f = new float[n];
f[i] = i;
delete [] f;
return 0;
}
Allocate the array during
runtime using new.
No garbage collection, so
you have to delete.
Dynamic memory is
useful when you don’t
know how much space
you need.

#include <iostream>
#include <vector>
int main() {
int n;
cin >> n;
vector<float> f(n);
f[i] = i;
return 0;
}
STL vector is a resizable
array with all dynamic
memory handled for you.
STL has other cool stuff,
such as strings and sets.
If you can, use the STL
and avoid dynamic
memory.

#include <iostream>
#include <vector>
int main() {
int n;
cin >> n;
vector<float> f;
f.push_back(i);
return 0;
}
An alternative method
that does the same thing.
Methods are called with
the dot operator (same as
Java).
vector is poorly named,
it’s actually just an array.

float twice1(float x) {
return 2*x;
}
void twice2(float x) {
x = 2*x;
}
int main() {
float x = 3;
twice2(x);
cout << x << endl;
return 0;
}
 This works as expected.
 This does nothing.
 The variable is
unchanged.

vector<float>
twice(vector<float> x) {
int n = x.size();
x[i] = 2*x[i];
return x;
}
int main() {
vector<float>
y(9000000);
y = twice(y);
return 0;
}
There is an incredible
amount of overhead here.
This copies a huge array
two times. It’s stupid.
Maybe the compiler’s
smart. Maybe not. Why
risk it?

void twice3(float *x) {
(*x) = 2*(*x);
}
void twice4(float &x) {
x = 2*x;
}
int main() {
float x = 3;
twice3(&x);
twice4(x);
return 0;
}
 Pass pointer by value
and
access data using
asterisk.
 Pass by reference.
 Address of variable.
 The answer is 12.

 You’ll often see objects passed by reference.
 Functions can modify objects without copying.
 To avoid copying objects (often const references).
 Pointers are kind of old school, but still useful.
 For super-efficient low-level code.
 Within objects to handle dynamic memory.
 You shouldn’t need pointers for this class.
 Use the STL instead, if at all possible.

 Classes implement objects.
 You’ve probably seen these in 6.170.
 C++ does things a little differently.
 Let’s implement a simple image object.
 Show stuff we’ve seen, like dynamic memory.
 Introduce constructors, destructors, const, and
operator overloading.
 I’ll probably make mistakes, so some debugging too.

 The C++ Programming Language
 A book by Bjarne Stroustrup, inventor of C++.
 My favorite C++ book.
 The STL Programmer’s Guide
 Contains documentation for the standard template library.
 http://www.sgi.com/tech/stl/
 Java to C++ Transition Tutorial
 Probably the most helpful, since you’ve all taken 6.170.
 http://www.cs.brown.edu/courses/cs123/javatoc.shtml

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