Chapter 11 Structure and Union Types Instructor: Alkar / Demirer
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.
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;
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;
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);
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.
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;
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.
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(¤t_planet); ” –The input argument is also used to store the result. “ *plnp ” is parenthesized because & operator has higher precedence.
Copyright ©2004 Pearson Addison-Wesley. All rights reserved & Data Areas of call to scan_planet (¤t_planet); plnp is a pointer which points to the same data area of current_planet.
Copyright ©2004 Pearson Addison-Wesley. All rights reserved 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).diameterdouble &(*plnp).diameterdouble *Address of diameter of current_planet structure “&(*plnp).diameter“&(*plnp).diameter” is evaluated as shown in the following table.
Copyright ©2004 Pearson Addison-Wesley. All rights reserved 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 ”.
Copyright ©2004 Pearson Addison-Wesley. All rights reserved 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.
Copyright ©2004 Pearson Addison-Wesley. All rights reserved Function Returning a Structured Result Type (2/2) Suppose the current time is 21:58:32, and the elapsed time is 97 seconds.
Copyright ©2004 Pearson Addison-Wesley. All rights reserved 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 = ; stulist[3].gpa = 3.0;
Copyright ©2004 Pearson Addison-Wesley. All rights reserved Arrays of Structures (2/2) The array of structures can be simply manipulated as arrays of simple data types.
Copyright ©2004 Pearson Addison-Wesley. All rights reserved 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.
Copyright ©2004 Pearson Addison-Wesley. All rights reserved 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.
Copyright ©2004 Pearson Addison-Wesley. All rights reserved 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.