Programming Languages Implementation of Data Structures

Programming LanguagesImplementation of Data Structures Cao Hoaøng Truï Khoa Coâng Ngheä Thoâng Tin Ñaïi Hoïc Baùch Khoa TP. HCM

Contents • Fundamentals • Elementary data types • Structured data types • Subprograms

Fundamentals • Data objects • Data types • Type specification and implementation • Declaration • Type checking, compatibility, and conversion • Assignment and initialisation

Data Objects • A run-time grouping of one or more pieces of data • A container for data values • Block of storage • Programmer-defined and system-defined • Lifetime • Variables and constants

Data Types • A class of objects having the same properties • Primitive data types

Specification • Attributes • Values • Operations: op_name: arg_type x arg_type x …  result_type x result_type x …

Examples: Arrays • Attributes: • number of dimensions • subscript range for each dimension • data types of the components • Values: valid values for the components • Operations: subscripting, creating, accessing attributes

Implementation • Storage representation • Operation definitions: • hardware operations • subprograms • in-line codes

Declaration • To provide information about data objects: • number and type • name and position • lifetime • constant and initialised value

Declaration • Data type declaration: • by name varA:integer • by specification varA:array [1..20]of integer

Declaration • Operation declaration: • argument number, order, data types • result number, order, data types functionFOO(X:integer; Y: real): real; FOO: integer x real  real

Declaration • Purposes: • choice of storage representations • storage management • generic operations • type checking

Type Checking • Checking if each operation receives the proper number of arguments of the proper data types • Dynamic (run time) vs. static (compile time) type checking

Type Checking • Dynamic type checking: • no declarations required • types of data objects may change as needed • programmers have no concerns about data types • difficult to debug and remove type errors • extra storage required for keeping type information • reduction of execution speed

Type Compatibility • T1 and T2 are compatible if data objects of type T1 can occur in the positions of data objects of type T2, and vice versa: name or structural equivalence typeVECT1:array [1..10] of real; VECT2:array [1..10] of real; varX, Y:VECT1; Z:VECT2; Y := X; Z := Y;

Type Compatibility • Name equivalence: • no anonymous types allowed • global type definitions used varX:array [1..10] of real;

Type Compatibility • Structural equivalence: • difficult to define • static type checking compromised • cost to check typeMETERS = integer; LITERS = integer; var LEN:METERS; VOL:LITERS; LEN + VOL

Type Conversion • When types are mismatched: • type error • type conversion (coercion) varA:integer; int I; B, C: real; unsigned U; float F; C := A + B I = - 1; U = 1; F = U * I; /* I = - 1  65535 */

Assignment • Basic operation for changing values of data objects • Specification: := : type1 x type2 void = : type1 x type2 type3 Z := X + Y Z = X + (Y = W * 2) A = B = C

Initialisation • To set a value in the storage of an data object • Un-initialised data object • Explicit and implicit initialisation

Programming LanguagesImplementation of Data Structures Cao Hoaøng Truï Khoa Coâng Ngheä Thoâng Tin Ñaïi Hoïc Baùch Khoa TP. HCM

Elementary Data Types • Numeric data types • Enumerations • Booleans • Characters

Numeric Data Types • Integers • Subranges • Floating-point real numbers • Fixed-point real numbers • Complex numbers • Rational numbers

Integers -32768  32768 2 bytes -65536  65536 4 bytes

Subranges • Smaller storage requirements • fewer bits than a general integer • software-simulated operations • Better type checking var A: 1..10

Floating-Point Real Numbers 6.7510 = 110.112 = 0.110112 x 23 = 0.110112 x 00112 Sign bit for exponent exponent 0 0 0011 11011 mantissa Sign bit for mantissa

Fixed-Point Real Numbers 6.7510 = 110.112 Sign bit integer part fractional part 0 110 11

Complex Numbers real part imaginary part

Rational Numbers • To avoid roundoff and truncation • Pairs of integers of unbounded length numerator denominator Sign bit

Enumerations type DEGREE = (bachelor, master, doctor) 0 1 2

Booleans • A particular bit • Zero/non-zero value 1 byte

Characters 1 byte 2 byte

Structured Data Types • Fundamentals • Vectors and arrays • Records • Character strings • Pointers • Sets • Files

Fundamentals • Specification • Implementation • Type checking

Specification • Attributes: • Number of components • Type of each component • Names for selecting components • Maximum number of components • Organization of components

Specification • Operations: • Component selection (random/sequential) • Whole-data-structure operations • Insertion/deletion • Creation/destruction

Implementation • Storage representation: Decriptor Decriptor Component Component Component Component Sequential Linked

Implementation • Selection operation: • Sequential  base-address-plus-offset • Linked  pointer following

Implementation • Storage management: object object Dangling References Garbage

Type Checking • Existence of a selected component: A[I] • Type of a selected component: A[2].link.item var A: array [1..10] ofreal;

Programming Languages Implementation of Data Structures