C++ Basic Concepts: Seong Jong Choi

Copyright, 2000 © Multimedia Lab.,

C++ Basic Concepts Seong Jong Choi [email protected] Multimedia Lab. Dept. of Electrical and Computer Eng. University of Seoul Seoul, Korea

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Seong Jong Choi

C++ Basic Concepts-1

1. Main Objectives • C++ Parsing 을 위한 기본 개념 소개 • Reference: from MSDN

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Seong Jong Choi

C++ Basic Concepts-2

Parser • 문장의 x 형식 : 주어 , 동사 , 목적어 , 보어 (language construct)

• 문법 (grammar) 에 의한 분류 • 문법을 표현하기 위한 여러 개념

Compiler

Translation Unit

Scanner (Lexical Analysis)

Token

Parser (Syntactic analysis or parsing)

Language Construct

Code Generation

Object file

White Space

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C++ - object file translation • int myInt; //declare &define an integer

Compiler

int myInt;

Scanner (Lexical Analysis)

1. int (keyword) 2. myInt (identifier) 3. ; (punctuation)

Parser (Syntactic analysis or parsing)

Code Generation

Object file

delcare and define myInt as an integer

//declare & ...

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1. int (type name) 2. myInt (variable) 3. ; (end of a statement)

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C++ Basic Concepts-4

Basic Concepts • • • • • • • • •

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Declaration Definition Lifetime Name Object Scope Storage class (Data) Type lvalue and rvalue

Seong Jong Choi

C++ Basic Concepts-5

Declaration & Definition // Declaration and definition demo // Declaration (not definition) of function sum (function prototype) int sum (int , int ); void main () { // declaration and definition of variables int a=10, b=20; int result; result = sum(a, b); } //Declaration and definition of function sum int sum (int x, int y) { int c; c = x + y; return c; } 12/04/09

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Declaration • Def) A declaration introduces names and their types into a program without necessarily defining an associated object or function. However, many declarations serve as definitions.

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Definition • Def) A definition provides information that allows the compiler to allocate memory for objects or generate code for functions.

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Lifetime • Def) The lifetime of an object is the period during which an object exists, including its creation and destruction.

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Name • Def) A name denotes an object, function, set of overloaded functions, enumerator, type, class member, template, value, or label. • C++ programs use names to refer to their associated language element. • Names can be type names or identifiers.

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Seong Jong Choi

C++ Basic Concepts-10

Object and Variable • Def) An object is an instance (a data item) of a user-defined type (a class type). • The difference between an object and a variable: – variables retain state information – objects can also have behavior.

• Note: – object means instance of a user-defined type – variable means instance of a fundamental type.

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C++ Basic Concepts-11

Scope • Def) Names can be used only within specific regions of program text. These regions are called the scope of the name. – – – – –

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Local scope function scope file scope class scope prototype scope

Seong Jong Choi

C++ Basic Concepts-12

Scope • Local scope

– A name declared within a block is accessible only within that block and blocks enclosed by it, and only after the point of declaration.

{

}

int a; …

– The names of formal arguments to a function in the scope of the outermost block of the function have local scope.

int func(int a) { … }

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C++ Basic Concepts-13

Scope • Function scope

• Labels are the only names that have function scope

• File scope

– Any name declared outside all blocks or classes has file scope. It is accessible anywhere in the translation unit after its declaration. – Names with file scope that do not declare static objects are often called “global” names.

• Class scope.

– Names of class members have class scope.

• Prototype scope.

– Names declared in a function prototype are visible only until the end of the prototype.

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Seong Jong Choi

C++ Basic Concepts-14

Scope • Hidden Names

– You can hide a name by declaring it in an enclosed block. – You can hide names with file scope by explicitly declaring the same name in block scope. However, file-scope names can be accessed using the scope-resolution operator (::).

#include int i = 7;      // i has file scope-declared outside all blocks void main( int argc, char *argv[] ) { int i = 5;  // i has block scope-hides the i with file scope cout << "Block-scoped i has the value: " << i << "\n"; cout << "File-scoped i has the value: " << ::i << "\n"; }

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Seong Jong Choi

C++ Basic Concepts-15

Storage Class • Def) The storage class of a named object determines its lifetime, initialization, and, in certain cases, its linkage. – – – –

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automatic static register external

Seong Jong Choi

C++ Basic Concepts-16

Storage Class • Automatic – Automatic objects in a function are (automatically) created when it is called and (automatically) destroyed when it ends. – Default unless otherwise specified – Usually, use stack for the storage

• Static Objects – Static objects are created and initialized once and live until the program terminates – Global, namespace scope, declared with static

static int a; // static declaration – A global object or variable that is explicitly declared as static has internal linkage (file scope). 12/04/09

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C++ Basic Concepts-17

(Data) Type • Definition: A type defined the proper use of a name or an expression.

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Type Hierachy

T y p e F u n d a m A r it h m F lo a t in g

B

e t ic

T y p e

e n t a l

T y p e

v o id

TI n y t pe eg r a l T y pA er r a y

o o l e a n C T hy ap re a c t e r I n T t ye pg e e r

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D D

ir e c t ly

F u n c t io n

P

D

e r iv e d

o in t e r

R

e r iv e d

T y p e

e f e r e n c Ce

T y p e C

o m

p o s e d

o n s t a n tS t r u c t u r e U n io n

C

D

e r

la s s

T y p e

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C++ Basic Concepts-19

Fundamental Types • Def) Fundamental types are built into the language (such as int, float, or double). • Instances of these fundamental types are often called “variables.”

T y p e F u n d a m A r i t h m F lo a t in g

B

e t ic

e n t a l

T y p e

TI n y t pe eg r a l

v o id

T y pA er r a y

o o l e a n C T h y ap r e a c t e r I n T t ye pg ee r

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T y p e

D D

ir e c t ly

F u n c t io n

P

D

e r iv e d

o i n t e r

R

e r iv e d

T y p e

T y p e

C

e f e r e n c Ce

o n s t a n tS

o m

U

p o s e d

t r u c t u r e n io n

C

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Derived Types • Def) Directly derived types are new types derived from fundamental types. 

T y p e F u n d a m A r i t h m F lo a t in g

B

e t ic

e n t a l

T y p e

TI n y t pe eg r a l

v o id

T y pA er r a y

o o l e a n C T h y ap r e a c t e r I n T t ye pg ee r

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T y p e

D D

ir e c t ly

F u n c t io n

P

D

e r iv e d

o i n t e r

R

e r iv e d

T y p e

T y p e

C

e f e r e n c Ce

o n s t a n tS

o m

U

p o s e d

t r u c t u r e n io n

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C++ Basic Concepts-21

Composed Derivative Types • Def) Composed Derivative types are new types created by combining existing types. •  

T y p e F u n d a m A r i t h m F lo a t in g

B

e t ic

e n t a l

T y p e

TI n y t pe eg r a l

v o id

T y pA er r a y

o o l e a n C T h y ap r e a c t e r I n T t ye pg ee r

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T y p e

D D

ir e c t ly

F u n c t io n

P

D

e r iv e d

o i n t e r

R

e r iv e d

T y p e

T y p e

C

e f e r e n c Ce

o n s t a n tS

o m

U

p o s e d

t r u c t u r e n io n

C

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Seong Jong Choi

C++ Basic Concepts-22

lvalue and rvalue • There are two values associated with a variable. – Its data value = variable’s rvalue – Its address value = variable’s lvalue

• Example:

a = a – 1; // 우변의 a 는 a 의 데이터값 (10), 좌변의 a 는 a 의 주소값 i = 7;            // Correct. A variable name, i, is an l-value. 7 = i;            // Error. A constant, 7, is an r-value. j * 4 = 7;        // Error. The expression j * 4 yields an r-value. *p = i;           // Correct. A dereferenced pointer is an l-value. const int ci = 7; // Declare a const variable. ci = 9;            // ci is a nonmodifiable l-value, so the assignment causes an // error message to be generated. ((i < 3) ? i : j) = 7; // Correct. Conditional operator (? :) returns an lvalue.

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Seong Jong Choi

C++ Basic Concepts-23