cpp:const_member_functions
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cpp:const_member_functions [2017/05/15 07:18] – gthanos | cpp:const_member_functions [Unknown date] (current) – external edit (Unknown date) 127.0.0.1 | ||
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====== Const μέθοδοι της κλάσης ====== | ====== Const μέθοδοι της κλάσης ====== | ||
- | Όταν δηλώνεται ένα αντικείμενο ως //const// (όπως παρακάτω), | + | Όταν δηλώνεται ένα αντικείμενο ως //const// (όπως παρακάτω), |
- | + | ||
- | <code cpp Point.cpp> | + | |
- | #include < | + | |
- | using namespace std; | + | |
- | + | ||
- | class Point { | + | |
- | int x, y; | + | |
- | public: | + | |
- | Point(int vx,int vy) { x = vx; y = vy; } | + | |
- | void setX(int vx) { x = vx; } | + | |
- | void setY(int vy) { y = vy; } | + | |
- | int getX() { return x; } | + | |
- | int getY() { return y; } | + | |
- | }; | + | |
- | </ | + | |
<code cpp Rectangle.cpp> | <code cpp Rectangle.cpp> | ||
#include < | #include < | ||
- | #include < | ||
- | #include < | ||
using namespace std; | using namespace std; | ||
- | |||
- | #include " | ||
class Rectangle { | class Rectangle { | ||
private: | private: | ||
int width, height; | int width, height; | ||
- | Point *origin; | ||
public: | public: | ||
- | Rectangle(int | + | Rectangle(int |
- | | + | |
- | | + | |
- | | + | |
- | | + | |
- | Point & | + | |
}; | }; | ||
- | Rectangle:: | + | Rectangle:: |
- | width = w; height = h; | + | |
- | origin = new (nothrow) Point( p.getX(), p.getY() ); | + | |
- | if(origin == NULL) { | + | |
- | cerr << " | + | |
- | exit(-1); | + | |
- | } | + | |
} | } | ||
- | Rectangle::~Rectangle() { | + | void Rectangle::setWidth(int width) { this-> |
- | delete origin; | + | void Rectangle::setHeight(int height) { this-> |
- | } | + | int Rectangle:: |
- | + | int Rectangle::getHeight() { return | |
- | void Rectangle::setOrigin(Point &p) { | + | |
- | if(origin!=NULL) | + | |
- | delete origin; | + | |
- | + | ||
- | origin = new (nothrow) Point( p.getX(), p.getY() ); | + | |
- | if(origin == NULL) { | + | |
- | cerr << " | + | |
- | exit(-1); | + | |
- | | + | |
- | } | + | |
- | + | ||
- | Point &Rectangle::getOrigin() { return | + | |
int main() { | int main() { | ||
- | | + | const Rectangle rect(10,5); |
- | | + | |
} | } | ||
</ | </ | ||
- | Στον παραπάνω κώδικα επιχειρήστε να διαβάσετε το πεδίο | + | Στον παραπάνω κώδικα επιχειρήστε να διαβάσετε την μεταβλητή |
<code cpp> | <code cpp> | ||
int main() { | int main() { | ||
- | | + | const Rectangle rect(10,5); |
- | | + | |
- | | + | |
} | } | ||
</ | </ | ||
- | Σε αυτή την περίπτωση λαμβάνετε το παρακάτω μήνυμα λάθους: | + | Σε αυτή την περίπτωση λαμβάνετε το παρακάτω μήνυμα λάθους |
< | < | ||
- | Rectangle.cpp: In function ‘int main()’: | + | Rectangle5.cpp: In function ‘int main()’: |
- | Rectangle.cpp:46:35: error: passing ‘const Rectangle’ as ‘this’ argument of ‘Point& | + | Rectangle5.cpp:26:25: error: passing ‘const Rectangle’ as ‘this’ argument of ‘int Rectangle::getWidth()’ discards qualifiers [-fpermissive] |
- | const Point p1 = rect.getOrigin(); | + | cout << |
- | | + | |
</ | </ | ||
- | Η επεξήγηση του παραπάνω μηνύματος είναι ότι εφόσον το αντικείμενο είναι //const// θα πρέπει και | + | Η επεξήγηση του παραπάνω μηνύματος είναι ότι εφόσον το αντικείμενο είναι //const// θα πρέπει και |
- | <code cpp> | + | < |
- | Point & | + | # |
- | </code> | + | using namespace std; |
- | ===== Επιστρεφόμενη τιμή | + | class Rectangle { |
+ | private: | ||
+ | int width, height; | ||
+ | public: | ||
+ | Rectangle(int width, int height); | ||
+ | void setWidth(int width); | ||
+ | void setHeight(int height); | ||
+ | int getWidth() | ||
+ | int getHeight() const; | ||
+ | }; | ||
- | Στον παραπάνω κώδικα αν και η συνάρτηση // | + | Rectangle:: |
+ | this-> | ||
+ | } | ||
+ | |||
+ | void Rectangle:: | ||
+ | void Rectangle:: | ||
+ | int Rectangle:: | ||
+ | int Rectangle::getHeight() const { return height; } | ||
- | <code cpp> | ||
int main() { | int main() { | ||
- | | + | const Rectangle rect(10,5); |
- | | + | |
- | | + | |
- | p1.setX(p1.getX()+1); | + | |
} | } | ||
- | < | + | </code> |
+ | |||
+ | ===== Υπερφόρτωση const και non-const συναρτήσεων ===== | ||
- | Για | + | Στον παραπάνω |
<code cpp Rectangle.cpp> | <code cpp Rectangle.cpp> | ||
#include < | #include < | ||
- | #include < | ||
- | #include < | ||
using namespace std; | using namespace std; | ||
- | |||
- | #include " | ||
class Rectangle { | class Rectangle { | ||
private: | private: | ||
int width, height; | int width, height; | ||
- | Point *origin; | ||
public: | public: | ||
- | Rectangle(int | + | Rectangle(int |
- | | + | |
- | | + | |
- | | + | |
- | | + | |
- | | + | |
+ | int getHeight(); | ||
}; | }; | ||
- | Rectangle:: | + | Rectangle:: |
- | width = w; height = h; | + | |
- | origin = new (nothrow) Point( p.getX(), p.getY() ); | + | |
- | if(origin == NULL) { | + | |
- | cerr << " | + | |
- | exit(-1); | + | |
- | } | + | |
} | } | ||
- | Rectangle::~Rectangle() { | + | void Rectangle::setWidth(int width) { this-> |
- | | + | void Rectangle::setHeight(int height) { this-> |
- | } | + | int Rectangle:: |
+ | int Rectangle:: | ||
+ | int Rectangle:: | ||
+ | int Rectangle:: | ||
- | void Rectangle:: | + | int main() { |
- | | + | |
- | delete origin; | + | |
- | | + | |
- | origin = new (nothrow) Point( p.getX(), p.getY() | + | |
- | | + | |
- | | + | |
- | exit(-1); | + | |
- | } | + | |
} | } | ||
+ | </ | ||
+ | |||
+ | <WRAP center round tip 80%> | ||
+ | Στο παραπάνω παράδειγμα, | ||
+ | </ | ||
+ | |||
- | const Point & | ||
- | int main() { | ||
- | const Point p(5,6); | ||
- | const Rectangle rect(1, | ||
- | const Point p1 = rect.getOrigin(); | ||
- | } | ||
- | </ | ||
- | int main() { | ||
- | const Point p(5,6); | ||
- | const Rectangle rect(1, | ||
- | const Point p1 = rect.getOrigin(); | ||
- | } | ||
- | </ | ||
- | < | ||
cpp/const_member_functions.1494832721.txt.gz · Last modified: 2017/05/15 06:18 (external edit)