1. Chapter 11 Structure and Union Types Instructor: Alkar / Demirer

2. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-2 User-Defined Structure Types recordsA database is a collection of information subdivided into records. record –A record is a collection of information of one data object (e.g., ID, name, and age of a student). structure typeC allows us to define a new data type (called structure type) for each category of a structured data object.

3. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-3 Declaring Structure Types (1/2) typedef struct struct_typeSyntax of the structure type: typedef struct{ type1 id1; type2 id2; … } struct_type; typedef struct student_info;E.g., typedef struct{ char[20] name; int age; } student_info;

4. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-4 Declaring Structure Types (2/2) student_infoDeclaration: student_info student1, student2 = {“Wang”, 18}; typedef struct student_info class_info;A hierarchical structure is a structure containing components which are also structures. typedef struct{ int NumOfStudents; student_info students[20]; } class_info;

5. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-5 Manipulating Structure Types (1/2) direct component selection operatorWe can reference a component of a structure by the direct component selection operator, which is a period. E.g., strcpy(student1.name, “Chao”); student1.age = 18; printf(“%s is in age %d\n”, student1.name, student1.age);

6. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-6 Manipulating Structure Types (2/2) direct component selection operatorThe direct component selection operator has the highest priority in the operator precedence. –student1.age+student2.age+…; –The value of student1.age is referenced first. The copy of an entire structure can be easily done by the assignment operator. –student1 = student2; –Each component in one structure is copied into the corresponding component in the other structure.

7. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-7 Function with a Structured Input Parameter (1/2) Suppose there is a structure defined as follows. planet_ttypedef struct{ char name[20]; double diameter; int moons; double orbit_time, rotation_time; } planet_t;

8. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-8 Function with a Structured Input Parameter (2/2) When a structure variable is passed as an input argument to a function, all its component values are copied into the local structure variable.

9. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-9 Function with a Structured Input/Output Argument &For the following function, we have to call it by “ scan_planet(&current_planet); ” –The input argument is also used to store the result. “ *plnp ” is parenthesized because & operator has higher precedence.

10. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-10 & Data Areas of call to scan_planet (&current_planet); plnp is a pointer which points to the same data area of current_planet.

11. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-11 Step-by-Step Analysis of the Indirect Reference ReferenceTypeValue plnpplanet_t *Address of structure refers to current_planet *plnpplanet_tReal structure of current_planet (*plnp).diameterdouble12713.5 &(*plnp).diameterdouble *Address of diameter of current_planet structure “&(*plnp).diameter“&(*plnp).diameter” is evaluated as shown in the following table.

12. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-12 Indirect Component Selection Operator In the above example, we use direct component selection operator: period.. –e.g., &(*plnp).diameter indirect component selection operator ->C also provides indirect component selection operator: ->. - > –e.g., “ &plnp - >diameter ” is the same as “ &(*plnp).diameter ”.

13. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-13 Function Returning a Structured Result Type (1/2) The structure variable can also be used as the return value of a function. Use direct component selection operator.

14. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-14 Function Returning a Structured Result Type (2/2) Suppose the current time is 21:58:32, and the elapsed time is 97 seconds.

15. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-15 Arrays of Structures (1/2) We can also declare an array of structures. E.g., typedef strucut{ int id; double gpa; } student_t; Usage: student_t stulist[50]; stulist[3].id = 92922023; stulist[3].gpa = 3.0;

16. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-16 Arrays of Structures (2/2) The array of structures can be simply manipulated as arrays of simple data types.

17. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-17 Union Types UnionUnion is a data structure which represents only one of the component in the declaration. union hair_tE.g., typedef union{ int wears_wig; char color[20]; } hair_t; Suppose we declare a vairable “ hait_t hair_data; ”. This hair_data contains either the wears_wig component or the color component but not both.

18. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-18 A Function Using a Union Structure hair_info_tSuppose we have a structure variable. typedef struct{ int bald; hair_t h; } hair_info_t We can use this structure to reference the correct component. Use the wears_wig component. Use the color component.

19. Copyright ©2004 Pearson Addison-Wesley. All rights reserved.11-19 Two Interpretations of the Union Variable hair_t The memory content of hair_t depends on which component is referenced. –The memory allocated for hair_t is determined by the largest component in the union. Referencing the correct union component is the programmer’s responsibility. The wears_wig component is referenced. The color component is referenced.