Chapter 11 Structure and Union Types J. H. Wang ( 王正豪 ), Ph. D. Assistant Professor Dept. Computer Science and Information Engineering National Taipei University of Technology

Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-2 User-Defined Structure Types record –a collection of information about one data object A database is a collection of information stored in a computer’s memory or in a disk file. –a database is subdivided into records

Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-3 Structure Type Definition Example –Name: Jupiter –Diameter: 142,800 km –Moons: 16 –Orbit time: 11.9 yr –Rotation time: hr structure type –a data type for a record composed of multiple components

Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-4 Structure Type Definition (Cont’d) #define STRSIZ 10 typedef struct { char name[STRSIZ]; double diameter; /* equatorial diameter in km */ int moons; /* number of moons */ double orbit_time, /* years to orbit sun once */ rotation_time; /* hours to complete one revolution on axis */ } planet_t;

Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-5 Structure Type Definition (Cont’d) A name chosen for a component of one structure may be the same as the name of a component of another structure or the same as the name of a variable. The typedef statement itself allocates no memory A variable declaration is required to allocate storage space for a structured data object –planet_t current_planet, previous_planet, blank_planet = {"", 0, 0, 0, 0};

Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-6 Structure Type Definition (Cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-7 Structure Type Definition (Cont’d) hierarchical structure –a structure containing components that are structures Example typedef struct { double diameter; planet_t planets[9]; char galaxy[STRSIZ]; } solar_sys_t;

Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-8 Structure Type Definition (Cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-9 Manipulating Individual Components of a Structured Data Object direct component selection operator –a period placed between a structure type variable and a component name to create a reference to the component

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure 11.1 Assigning Values to Components of Variable current_planet

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Manipulating Individual Components of a Structured Data Object (Cont’d) printf("%s's equatorial diameter is %.1f km.\n", current_planet.name, current_planet.diameter); –Jupiter's equatorial diameter is km.

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Review of Operator Precedence In a generic expression containing two of the same operators in sequence: –operand1 op operand2 op operand3

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Review of Operator Precedence (Cont’d) Left associativity –(operand1 op operand2) op operand3 Right associativity –operand1 op (operand2 op operand3)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Manipulating Whole Structures With no component selection operator refers to the entire structure –previous_planet = current_planet;

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Program Style Naming Convention for Types To help reduce confusion, choose user- defined type names ending in the suffix _t.

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Structure Type Data as Input and Output Parameters When a structured variable is passed as an input argument to a function, all of its component values are copied into the components of the function’s corresponding formal parameter. When such a variable is used as an output argument, the address-of operator must be applied. The equality and inequality operators cannot be applied to a structured type as a unit.

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure 11.2 Function with a Structured Input Parameter print_planet(current_planet);

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure 11.3 Function Comparing Two Structured Values for Equality

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure 11.4 Function with a Structured Output Argument

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Structure Type Data as Input and Output Parameters (Cont’d) In order to use scanf to store a value in one component of the structure whose address is in plnp, we must carry out the following steps (in order): 1.Follow the pointer in plnp to the structure. 2.Select the component of interest. 3.Unless this component is an array (e.g., component name in Fig. 11.4), get its address to pass to scanf. &*plnp.diameter would attempt step 2 before step 1.

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Structure Type Data as Input and Output Parameters (Cont’d) indirect component selection operator –the character sequence -> placed between a pointer variable and a component name creates a reference that follows the pointer to a structure and selects the component two expressions are equivalent. –(*structp).component –structp->component

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Structure Type Data as Input and Output Parameters (Cont’d) result = scanf("%s%lf%d%lf%lf", plnp->name, &plnp->diameter, &plnp->moons, &plnp->orbit_time, &plnp->rotation_time);

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure 11.5 Data Areas of main and scan_planet during Execution of status = scan_planet (&current_planet);

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Structure Type Data as Input and Output Parameters (Cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Functions Whose Result Values Are Structured The function does not return the address of the structure as it would with an array result; rather it returns the values of all components.

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure 11.6 Function get_planet Returning a Structured Result Type current_planet = get_planet(); However, scan_planet with its ability to return an integer error code is the more generally useful function.

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure 11.7 Function to Compute an Updated Time Value typedef struct { int hour, minute, second; } time_t; time_now = new_time(time_now, secs);

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure 11.8 Structured Values as a Function Input Argument and as a Function Result

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Abstract Data Type abstract data type (ADT) –a data type combined with a set of basic operations We must also provide basic operations for manipulating our own data types. If we take the time to define enough basic operations for a structure type, we then find it possible to think about a related problem at a higher level of abstraction.

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure 11.9 Data Type planet_t and Basic Operations

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Parallel Arrays and Arrays of Structures Parallel Arrays int id[50]; /* id numbers and */ double gpa[50]; /* gpa's of up to 50 students */ double x[NUM_PTS], /* (x,y) coordinates of */, y[NUM_PTS]; /* up to NUM_PTS points */ Array of Structures –A more natural and convenient organization is to group the information in a structure whose type we define.

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Parallel Arrays and Arrays of Structures (Cont’d) Example #define MAX_STU 50 typedef struct { int id; double gpa; } student_t;... { student_t stulist[MAX_STU]; Example #define NUM_PTS 10 typedef struct { double x, y; } point_t;... { point_t polygon[NUM_PTS];

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Parallel Arrays and Arrays of Structures (Cont’d) stulist[0].id stulist[0].gpa for (i = 0; i < MAX_STU; ++i) scan_student(&stulist[i]); for (i = 0; i < MAX_STU; ++i) printf("%d\n", stulist[i].id);

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure An Array of Structures

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Union Types union –a data structure that overlays components in memory, allowing one chunk of memory to be interpreted in multiple ways typedef union { int wears_wig; char color[20]; } hair_t; hair_t hair_data; hair_data does not contain both wears_wig and color components, but either a wears_wig component referenced by hair_data.wears_wig, or a color component referenced by hair_data.color. The amount of memory is determined by the largest component of the union.

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Union Types (Cont’d) typedef struct { int bald; hair_t h; } hair_info_t; base our manipulation on the value of the bald component Referencing the appropriate union component is always the programmer’s responsibility; C can do no checking of the validity of such a component reference.

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Function That Displays a Structure with a Union Type Component

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Two Interpretations of Parameter hair

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Program to Compute Area and Perimeter of Geometri c Figures

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Program to Compute Area and Perimeter of Geometric Figures (cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Program to Compute Area and Perimeter of Geometric Figures (cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Program to Compute Area and Perimeter of Geometric Figures (cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Common Programming Errors Write your own type-specific equality and I/O functions. Place the union within another structure that contains a component whose value indicates which interpretation of the union is correct.

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Partial Implementation of Type and Operators for Complex Numbers

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Partial Implementation of Type and Operators for Complex Numbers (cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Partial Implementation of Type and Operators for Complex Numbers (cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Partial Implementation of Type and Operators for Complex Numbers (cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Partial Implementation of Type and Operators for Complex Numbers (cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Universal Measurement Conversion Program Using an Array of Structures

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Universal Measurement Conversion Program Using an Array of Structures (cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Universal Measurement Conversion Program Using an Array of Structures (cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Universal Measurement Conversion Program Using an Array of Structures (cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Universal Measurement Conversion Program Using an Array of Structures (cont’d)

Copyright ©2004 Pearson Addison-Wesley. All rights reserved Figure Data File and Sample Run of Measurement Conversion Program