Latest revision as of 04:25, 11 July 2012

Lecture 14, ECE264, Spring 2012, Prof. Lu

Lecture 14 - John Ribeiro

typedef struct {

 char *name;
 int year;
 int month;
 int date;

} Person;

Person Person_construct ( char * n , int y, int m, int d ) {

 Person p;
 p.name = malloc ( sizeof(char) * ( stnlen(n) + 1 ) );
 strcpy(p.name, n );
 p.year = y;
 p.month = m;
 p.date = d;
 return p;

}

void Person_destruct ( Person p ) {

 free ( p.name );

}

DEEP COPY (AVOID):

Person Person_copy ( Person p ) {

 return Person_constructor(p.name, p.year, p.month, p.date);

}

Person Person_assign ( Person p1, Person p2 ) {

 Person_destruct (p1);
 return Person_copy(p2);

}

--

Person p1 = Person_construct ("alice", 1980, 10, 21); Person p2 = Person_construct ("genny", 1984, 2, 5 ); Person p3 = Person_copy (p1); p3 = Person_assign (p3, p2);

Person_destruct(p1); Person_destruct(p2); Person_destruct(p3);

Why constructor?

• • A single place where all attributes are assigned
  • malloc in constructor

 - destructor_copy, assign

typedef struct {

 int year;
 int month;
 int date;

} DateofBirth;

typedef struct {

 char *name;
 DateofBirth dob;

} Person;

• When Person returns, the compiler will copy attribute by attribute

If P3 = P1; // Shadow copy

A shadow copy is when two pointers are assigned the same value in memory i.e the point to the same place

int x = 24; int y = x; x = 31 y = 31;

What is y?

Copy on Write - if one pointer changes memory

/////////////////////////////////////////////

LECTURE NOTES_2/23_Kailu Song

(WHY CONSTRUCTOR? a single place where all attributes are assigned) (malloc in constructor = copy+assign+destructor)

typed of struct {

 char *name;(if structure don't have pointer can write pointer Person P3 = P1; if copy attribute by attribute will get shallow copy)
 int year;
 int month;
 int data;

} Person; Person Person_construct(char *n, int y, int m, int d) {

 Person P;
 P.name = malloc(sizeof(char)*strlen(n)+1);
 (check if P.name is = NULL)
 strepy(P.name,n);
 P.year = y;
 P.month = m;
 P.date = d;
 return P;

} void Person_destruct(Person P) {

 free(P.name);

} Person Person_coty(Person P) {

 return Person_construct(P.name,P.year,P.month,P.data);  (inside the construct function,there is a malloc, so create another heap memory)

} Person Person_assign(Person P1, Person P2) {

 Person_destruct(P1);
 return Person_copy (P2);

} Person P1 = Person_construct("Amy",1980,10,21); Person P2 = Person_construct("Jennifer",1981,2,5); Person P3 = Person_copy(P1); P3 = Person_assign(P3,P2);(if change this line to P3 = Person_copy(P2),P2 will become leak memory become there are two mallocs) Person_destruct(P1); Person_destruct(P2); Person_destruct(P3);

HINT FOR IPA1-3: Maze_traverse(Maze xmz, int from, int *forward) {

if (canMove(east))
 {
   forward = 1;
   from = west;
   Maze_traverse(...east);
   book leaping;(dead end)
 }
if (canMove(south))
 {
   forward = 1;
   from = west;
   Maze_traverse(...south);
   book leaping;(dead end)
 }
if (canMove(west))
 {
   forward = 1;
   from = west;
   Maze_traverse(...west);
   book leaping;(dead end)
}
if (canMove(north))
 {
   forward = 1;
   from = west;
   Maze_traverse(...north);
   book leaping;(dead end)
}

canMove { CHECK whether it is a brick; CHECK where you come from; CHECK whether *forward = 1; }

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