introduction to c++web.cs.wpi.edu/.../lectures_a12/week3_introtoc++.pdf · introduction to c++...

Carnegie Mellon Worcester Polytechnic Institute

Introduction to C++

Professor Hugh C. Lauer CS-2303, System Programming Concepts (Slides include materials from The C Programming Language, 2nd edition, by Kernighan and Ritchie, Absolute C++, by Walter Savitch, The C++ Programming Language, Special Edition, by Bjarne Stroustrup, and from C: How to Program, 5th and 6th editions, by Deitel and Deitel)

Introduction to C++ CS-2303, A-Term 2012 1

Carnegie Mellon Worcester Polytechnic Institute Worcester Polytechnic Institute

Reading

Absolute C++, Chapter 1 Tour of C++

Absolute C++, Chapter 6 Classes and structs

Advice Don’t panic! All will become clear in time. You don’t need to know every detail of C++ to write good

programs Focus on programming techniques, not language details



What Is C++?

C — with a few minor syntactic differences Files & I/O Use new and delete

instead of malloc() and free() Inline Functions …

Template C++ For defining and

creating templates

Object-oriented C++ Classes Inheritance and Multiple

Inheritance Function and Operator

Overloading References and Reference

Parameters Default Arguments

Standard Template Library Many tools Templates for containers


Note: Objective C was invented at about the same time, with similar goals.

A federation of (at least) four languages


Compiling C++

Use gcc, Eclipse, Visual Studio, etc. See Lab #1

File types .cc, .cp, .cpp, .CPP, .cxx, .c++, .C .h, .H

In Linux gcc will recognize C++ file extensions and compile them

– but won’t get the libraries and defaults right g++ will set language to C++ and link to correct libraries by

default


Some of these have special properties.


In this Topic

A Simple C++ Example C++ Input/Output

Similarities and differences between C and C++ Brief tour of Chapters 4 & 5

References and Reference Parameters Namespaces

Including scope resolution operator "::"



A Simple C++ Example


// C++ simple example #include <iostream> //for C++ Input and Output int main () { int number3; std::cout << "Enter a number:"; std::cin >> number3; int number2, sum; std::cout << "Enter another number:"; std::cin >> number2; sum = number2 + number3; std::cout << "Sum is: " << sum <<std::endl; return 0; }

stream extraction operator standard input stream object

C++ style comments

stream manipulator Concatenating insertion operators

standard output stream object stream insertion operator


Simple C++ Program (continued)

<iostream> Must be included for any program that outputs data to

the screen or inputs data from the keyboard using C++ style stream input/output. Replaces <stdio.h> of C

C++ requires you to specify the return type, possibly void, for all functions. Specifying a parameter list with empty parentheses is

equivalent to specifying a void parameter list in C.



Notes on Simple C++ Program Stream manipulator std::endl Outputs a newline. Flushes the output buffer

The notation std::cout specifies a name (cout)

that belongs to the namespace std.


Note: std::ends flushes the buffer but does not add newline.

To be explained later


Header Files

C++ Standard Library header files Each contains a portion of the Standard Library.

Function prototypes for the related functions Definitions of various class types and functions Constants needed by those functions

“Instruct” the compiler on how to interface with library and user-written components. Use #include directive to include class or interface in a

program.


Note: You may encounter standard header file names ending in .h or .H • These are “old-style” header files • They are superseded by the C++

Standard Library header files


C++ Standard Library header files <iostream> <iomanip> <fstream> <ifstream>, <ofstream>

<string> <cstring>

<cstdlib> <cmath> <complex>, <numeric>

<ctime> <iterator> …

<vector> <list> <queue> <stack> <deque> <map> <set> <bitset>



Libraries for Next Assignment For PA4 <ifstream>

stream input from file <ofstream>

stream output to file <string>

String management



Keywords Shared with C


C++ keywords

Keywords common to the C and C++ programming languages

auto break case char const

continue default do double else

enum extern float for goto

if int long register return

short signed sizeof static struct

switch typedef union unsigned void

volatile while


New Keywords in C++


C++ keywords

C++-only keywords

and and_eq asm bitand bitor

bool catch class compl const_cast

delete dynamic_cast explicit export false

friend inline mutable namespace new

not not_eq operator or or_eq

private protected public reinterpret_cast static_cast

template this throw true try

typeid typename using virtual wchar_t

xor xor_eq


Types and Declarations Integer and floating point types

Much like C

bool Values true and false Use instead of C zero and non-zero

char and wchar_t char: usually 8 bits, implementation dependent wchar_t: larger character sets – Unicode, international character

sets, etc.

Enumerations Like C

Declarations, initializations, typedefs A lot like C


Beware! C++ will convert between integers and bool without telling you!


Ch. 5 – Pointers, Arrays, and Structs Pointers — like pointers in C

May point to any type T or to void Unary '&' operator means “create a pointer” Unary ‘*' operator means “dereference a pointer”

Simple arrays A lot like C May have any type T as elements Related to pointers as in C

However, Use vector or valarray containers from Standard Template

Library (STL)


Recommend Advice:– Use 0 (i.e.,zero) instead of NULL


Ch. 5 – Pointers, Arrays, and Structs (continued)

In C, we introduced a struct as “like a Java class, but with no methods”

In C++, a struct IS A class! The keyword struct can be used wherever the keyword class

can be used An vice versa!

The ONLY difference is that members of a struct are, by default, public

class members are by default private


public and private access specifiers may be included anywhere in a struct or a class


structs and classes (continued)

By definition:– struct s { …

is shorthand for class s { public: …

Stylistic advice:– Use struct when ALL members are public; otherwise,

use class



struct example

Example:– struct address{

char * name; long int number; char * street; char * town; char state[2]; long zip;

}; //requires a semicolon after '}'

Usage:– address jd; // don’t need to say “struct” as we did in C jd.name = “Jim Dandy”; jd.number = 61;



Type Equivalence Two structs are different types, even when the have

identical members §5.7.1

Example struct S1 { int a; }; struct S2 { int a; }; S2 = S1; // illegal!



Questions?



Memory Allocation from Heap

new and delete for structs, classes, etc. Example

class Table { …} … Table *p = new Table; //allocate and initialize Table *q = new Table; //new objects from Heap … delete p; // free objects, clean up, delete q; // return memory to Heap

See §10.1, Absolute C++



Memory Allocation (continued)

new and delete[] for arrays Example

char * s = new char[length]; // allocate new arrays int * t = new int[count]; // from Heap … s[i] = 'x'; // use arrays as in C int x = t[j]; … delete[] s; // free whole arrays, return delete[] t; // memory to Heap

See §10.2


It is usually incorrect to say delete s; delete t;


Memory Allocation (concluded)

Always use new and delete or delete[]

Never, ever use malloc() and free() malloc() doesn’t correctly initialize objects

Especially class objects! free() doesn’t correctly destroy objects

Especially class objects! delete doesn’t correctly destroy individual objects of

arrays Must use delete[]



Questions?



References in C++

Definition Reference:– An Alternative Name for an object

BIG difference from Java

References are only created in declarations and parameters

A reference can only appear where the object itself could have appeared

See §8.3 in Absolute C++



Simple References void f() {

int j = 1; int &r = j; //r and j refer to the exact same int int x = r; // x now is 1 r = 2; // j now is 2

} //f int k; int &r1 = k; // okay: r1 is initialized int &r2; // error; initializer missing extern int &r3; //okay; r3 defined elsewhere


Sometimes, reference declarations are written as int& r1 = k;


Simple References (continued)

void g() { int ii = 0; int &rr = ii; rr++; // ii now is 1 int *pp = &rr; // pp now points to ii

} //g


Note: This declares a pointer exactly as in C, and initializes it with the address of rr (which is another name for ii)


Example Usage of a Reference int grid[1000];

int rowSize, x, y; ... int &element = grid[x*rowSize+y];

... /* computations on integer named element */



Reference Parameters

An alias for its corresponding argument in a function call. & placed after the parameter type in the function

prototype and function header Example int &count in a function header

Pronounced as “count is a reference to an int”

Parameter name in the called function body actually refers to the original variable in the calling function.



Reference Parameter Example

C version void swap (int *a, int *b) {

int temp = *a; *a = *b; *b = temp;

} // void swap(…)

C++ version void swap (int &a, int &b) {

int temp = a; a = b; b = temp;

} // void swap(…)


Hazard: a NULL pointer

Non-hazard: no pointer here


Notes on References and Pointers Pointers in C do multiple duty Links, as in linked lists and trees Parameters, where the function needs to return a value to an

argument provided by the caller Short-hand, a short way of referring to an object that otherwise

would need a complex expression …


C++ introduces references to address both of these cases


Java vs. C++ References

In Java, a reference is a data type. It can be assigned to, compared, copied, stored, etc. Same reference variable can refer to different objects at

different times during execution

In C++, a reference is an alias for an object It cannot be assigned to; assignment is through the reference

to the underlying object – Similar to dereferencing a pointer in C

It cannot be compared; comparison applies to underlying object

A reference always refers to the same object for the duration of its scope



Repeat Three Times

A C++ reference is not a pointer, … A C++ reference is not a pointer, … A C++ reference is not a pointer, … And neither of them resembles a

Java reference



Questions?



Namespace A logical grouping of names

… to set them apart from other names

… to avoid conflicts among similar names

See §8.2



Namespace Example


// C++ simple example #include <iostream> //for C++ Input and Output int main () { int number3; std::cout << "Enter a number:"; std::cin >> number3; int number2, sum; std::cout << "Enter another number:"; std::cin >> number2; sum = number2 + number3; std::cout << "Sum is: " << sum <<std::endl; return 0; }

From slide #7


Namespaces (continued)

Names cout, cin, endl are declared in <iostream> …

… but are not directly visible to program

The are part of namespace std … which is visible!

Need scope resolution operator '::‘ To get at things from a namespace



Scope Resolution Operator

std::cout The object cout that is declared in namespace std

void BinaryTree::PrintTree The method PrintTree that is declared in class

BinaryTree (needed when implementing PrintTree)



“Using” Directive #include <iostream>

using std::cout; using std::cin; using std::endl; …

int main() { double sideValue;

cout << "\nEnter the side " " length of your cube: "; cin >> sideValue;

cout << "Volume of cube with “ "side " << sideValue << " is " << cube( sideValue ) << endl; return 0; } // int main()


Adds cout, cin, endl from namespace std to current scope

These names may now be used without qualification


Common C++ Programming Error Forgetting to say “Using” You get undeclared identifiers Even though you include the appropriate header file!

Using std Bad style Makes all names in namespace std visible … whether you need them or not!



Questions?


introduction to c++web.cs.wpi.edu/.../lectures_a12/week3_introtoc++.pdf · introduction to c++...

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