Chapter 10 - C structures and unions, PPT, PF, Semester, Engineering - Computer Science Engineering (CSE) PDF Download

Introduction

The slides cover the following topics:

1. C structures
2. Strucuture Declarations
3. Recursively defined structures
4. Member access
5. Memory layout
6. Bit fields
7. Structures as function arguments
8. Unions

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C structures: aggregate, yet scalar

   •named members hold data items of various types

   •like the notion of class/field in C or C++

  – but without the data hiding features

  (rationale: too inefficient)

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Structure declarations

struct tag {member-list} variable-list;

struct {int a, b; char *p;} x, y;  /* omit tag */

  int members a, b and char pointer p.

  even if there is another declaration:

struct {int a, b; char *p;} z;

  /* z has different type from x, y */

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Structure declarations

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Recursively defined structures

struct TREENODE {

  char *label;

  struct TREENODE *leftchild, *rightchild;

}

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Recursively defined structures

struct HUMAN;

struct PET {

  char name[NAME_LIMIT];

  char species[NAME_LIMIT];

  struct HUMAN *owner;

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Member access

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Memory layout

struct COST { int amount;

              char currency_type[2]; }

struct PART { char id[2];

              struct COST cost;

              int num_avail; }

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Memory layout

A better alternative (from a space perspective):

struct COST { int amount;

              char currency_type; }

struct PART { struct COST cost;

              char id[2];

              int num_avail;

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Bit fields

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Bit fields

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Structures as function arguments

struct BIG changestruct(struct BIG s);

  – involves a lot of copying

void changestruct(struct BIG *s);

void changestruct(struct BIG const *s);

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Unions

union VALUE {

  float f;

  int i;

  char *s;

};

/* either a float xor an int xor a string */

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Unions

C structures and unions---------------------------------------------Next slide

Unions

  for the larger data types, consider using pointers instead