C++ (intro)

Hwansoo Han

Why New Languages?

Already know

C, Java, Python, Matlab, …

C++

Basically extension to C

All C code compiled with C++ compilers

But many libraries and “OO” concepts added

2

Many Use C++

Most recent open source projects

Written in C++ or Java

Easier to understand – “OO” design

Natural extension to C

C and C++ can be easily mixed (with a little efforts)

3

Hello, World!

4

/*

* First program in C++ : hello world

*/

#include <iostream>

using namespace std;

// main function

int main()

{

cout << “hello, world!” << endl;

return 0;

}

console output

C++ IDE

Download Eclipse CDT (C/C++ development tooling)

www.eclipse.org/downloads

Download “Eclipse IDE for C/C++ Developers”

Unzip the downloaded file into a directory

E.g. D:\bin\

Download JRE 6.0 or above

Google “JRE 64bit windows 7”

E.g. Downloads.cnet.com

Run the downloaded file to install JRE

5

Genealogy of Programming Languages

6

C++ vs. C vs. Java: Minor Differences

Boolean type

C: int myBooleanValue = 1;

C++: bool myBooleanValue = true;

Java: boolean myBooleanValue = true;

Printing

C: printf(“Hello!\n”);

C++: cout << “Hello!” << endl;

Java: println(“Hello!”);

7

C++ vs. C vs. Java: Minor Differences

Calling other functions

C/C++ : define before use

Java : no such worries

void PrintHello();

void PrintTime() { cout << “It’s time to go!” << endl; }

int main() {

PrintHello(); // OK – Prototype defined earlier

PrintTime(); // OK – Function defined earlier

SayHi(); // ERROR – no prototype earlier

}

void PrintHello() { cout << “Hello!” << endl; }

void SayHi() { cout << “Hi!” << endl; }

8

C++ vs. C vs. Java: Major Differences

9

C/C++ has no garbage collector

Java: Integer myInt = new Integer();

myInt = NULL; // GC will delete

C++ : programmers need to delete

C : programmers need to free

Objects

Java : memory for all objects is put on the heap

C++ : Objects can be placed either on the stack or the heap

C : no objects, malloc gets the space from the heap

Program Images, Variables, Objects

10

Address space

Local variables : stack

Global variables : data

Dynamically allocated objects : heap

code

data

heap

stack

kernel 0xC0000000

0xFFFFFFFF

0x080482d0

int a = 1; // ?

int main() {

int b = 1; // ?

int *c; // ?

c = (int*)malloc(sizeof(int)); // ?

}

C++ vs. C vs. Java: Major Differences

11

Stack vs. Heap allocation in C/C++

int main() {

int a = 1; // STACK

int b(2); // STACK

int *c = new int(3); // HEAP

cout << “a=“ << a << “ addr=“ << &a << endl;

cout << “b=“ << b << “ addr=“ << &b << endl;

cout << “c=“ << *c << “ addr=“ << c << endl;

delete c;

}

int fn() {

int *parray = new int [10]; // STACK

// …

delete [] parray;

}

C++ vs. C vs. Java: Major Differences

12

C++ can choose to pass by value, pointer, and reference

C can choose to pass by value or pointer

Java cannot choose

Primitives only pass by value

Objects only pass by reference

/* Java */

void AddOne(int x) { x++; }

void run() {

int x = 7;

AddOne(x);

println(x); // output 7

}

/* C++ */

void AddOne(int &x) { x++; }

int main() {

int x = 7;

AddOne(x);

cout << x << endl; // output 8

}

/* C */

void AddOne(int *x) { (*x)++; }

int main() {

int x = 7;

AddOne(&x);

printf(“%d\n”, x); // output 8

}

Coding Style – Managing Large Code

13

Instead putting all into a single file, separate them for

easier management

Files with extension .cpp/.cc contains implementations of

functions

Files with extension .h contains function prototype

.h files are used to overall shape of source code

Other programmers can roughly recognize your programs

through header files (.h files)

If you don’t care the details on how a function works, you

don’t have to look into .cpp files.

C++ vs. C vs. Java: Similarities

14

Short circuit evaluation

if (x < 4 || y == 3) // test the first (x<4), if true skip the second

Integer division

9/4 ⇒ 2

Primitives

char, short, int, long, float, double

Type conversion

3/2.0 ⇒ 1.5

10 + 8.2 ⇒ 18.2

Functions, objects (C++/Java), arithmetic operators, …

Makefile - Example

15

target: dependency_list

[TAB]command_list

$@ : name of target

$^ : dependecy_list

First target is a default target

> make

> make all

> make random

> make clean

Comment

Variable definition

List of targets

# Makefile for hello, mem, and random

CXXFLAGS = -O3 –Wall

CXX = g++

PROGRAMS = hello mem random

all: $(PROGRAMS)

hello: hello.cpp

$(CXX) $(CXXFLAGS) –o $@ $^

mem: mem.cpp

$(CXX) $(CXXFLAGS) –o $@ $^

random: random.cpp

$(CXX) $(CXXFLAGS) –o $@ $^

clean:

rm –f $(PROGRAMS)

@echo “--binaries are removed”