Which constructor gets called while i create an array of , C/C++ Programming

Which constructor gets called while I create an array of Fred objects?

Posted Date: 3/15/2013 5:58:17 AM | Location : United States





A: Fred''s default constructor

class Fred { public: Fred();

...

};

int main()

{

Fred a[10];  calls the default constructor 10 times

Fred* p = new Fred[10]; calls default constructor 10 times

...

}

If your class doesn''t contain a default constructor, you''ll get a compile-time error while you try to create an array by using the above simple syntax:

class Fred {

public:

Fred(int i, int j); suppose there is no default constructor

...

};

int main()

{

Fred a[10]; ERROR: Fred doesn''t contain a default constructor

Fred* p = new Fred[10]; ERROR: Fred doesn''t contain a default constructor

...

}

Though, even if your class already contain a default constructor, you must try to use std::vector instead of an array (arrays are evil). Std::vector allows you decide to use any constructor, not only the default constructor:

#include int main()

{

std::vector a(10, Fred(5,7));  the 10 Fred objects in std::vector a will be initialized along with Fred(5,7)

...

}

Although you have to use a std::vector instead of an array, there are times while an array may be the right thing to do, and for those, you may need the "explicit initialization of arrays" syntax. Here''s how:

class Fred {

public:

Fred(int i, int j);  assume there is no default constructor

...

};

int main()

{

Fred a[10] = {

Fred(5,7), Fred(5,7), Fred(5,7), Fred(5,7), Fred(5,7), // The 10 Fred objects are

Fred(5,7), Fred(5,7), Fred(5,7), Fred(5,7), Fred(5,7) // initialized using Fred(5,7)

};

...

}

Certainly you don''t contain to do Fred(5,7) for every entry you can put in any numbers you wish, even parameters or other variables.

Lastly, you can use placement-new to initialize manually the elements of the array. Warning: it''s unattractive: the raw array can''t be of type Fred, so you''ll require a bunch of pointer-casts to do things such as compute array index operations. Warning: its compiler- and hardware-dependent: you''ll require making sure the storage is aligned along with an alignment i.e. at least as strict as is needed for objects of class Fred. Warning: it''s boring to make it exception-safe: you''ll require to manually destructing the elements, by including in the case while an exception is thrown part-way through the loop which calls the constructors. But if you really wish to do it anyway, read up on placement- new. (BTW placement-new is like magic which is used inside of std::vector. The difficulty of getting everything right is still another reason to use std::vector.)

By the way, did I ever denote that arrays are wicked? Or did I denote that you have to use a std::vector unless there is a compelling cause to use an array?

 

Posted by | Posted Date: 3/15/2013 5:58:52 AM


Related Discussions:- Which constructor gets called while i create an array of , Assignment Help, Ask Question on Which constructor gets called while i create an array of , Get Answer, Expert's Help, Which constructor gets called while i create an array of Discussions

Write discussion on Which constructor gets called while i create an array of
Your posts are moderated
Related Questions
Derived Data Type: Array is derived data type to store large collection of data of only one data type. int mark[100]; char names[25]; Function: will be discussed early

Write a function to calculate the exchange rate of pounds to dollars  Answer       Td = 2xTp   The parameter passed over is the number of pounds and returned the value in do

write a program to find the area under the curve y=f(x) between x=a & x=b


write a program in c/C++ using nested if statement for calculating the average marks and grades of 5 subjects

WAP TO ACCEPT MARKS OF THREE SUBJECT FOR STUDENT & CALCULATE TOTAL MARKS AND PERCENTAGE #include stdio.h> #include conio.h>   void main() {            int M1,M

write a program to find the minimum number of shelves

#question.to determine the area of a triangle,rectangle and trapezium

write aprogram in c++ to overload +,-,=,++ operator using unary and friend function in a single program

write a program to find area of curve y=f(x) between x and x=b,integrate between the limits a and b using c     #include float start_point, /* GL