Questions tagged [empty-class]
21 questions
61
votes
4 answers
Empty class object in Python
I'm teaching a Python class on object-oriented programming and as I'm brushing up on how to explain classes, I saw an empty class definition:
class Employee:
pass
The example then goes on to define a name and other attributes for an object of…
Ramy
- 20,541
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44
votes
3 answers
What function does C++ write and call in an empty class?
In the book Effective C++, I saw the passage below:
As a result, if you write
class Empty{};
it's essentially the same as if you'd written this:
class Empty {
public:
Empty() { ... }
Empty(const Empty& rhs) { ... }
~Empty() { ...…
llinvokerl
- 1,029
- 10
- 25
16
votes
3 answers
Why is the empty base class optimization (EBO) is not working in MSVC?
Why is the empty base class optimization (EBO) not being fully applied in Visual C++?
If I have a lot of base classes, is there any way for me to help the compiler make this optimization?
#include
struct T1 { };
struct T2 { };
struct T3…
user541686
- 205,094
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15
votes
8 answers
what is the size of empty class in C++,java?
What is the size of an empty class in C++ and Java?
Why is it not zero?
sizeof(); returns 1 in the case of C++.
garima
- 5,154
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11
votes
2 answers
why a const object of an empty class cant be created
#include
class A {
public:
void foo() const {
std::cout << "const version of foo" << std::endl;
}
void foo() {
std::cout << "none const version of foo" << std::endl;
}
};
int main()
{
A…
Haiyuan Zhang
- 40,802
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11
votes
3 answers
Handles Comparison: empty classes vs. undefined classes vs. void*
Microsoft's GDI+ defines many empty classes to be treated as handles internally. For example, (source GdiPlusGpStubs.h)
//Approach 1
class GpGraphics {};
class GpBrush {};
class GpTexture : public GpBrush {};
class GpSolidFill : public GpBrush…
Nawaz
- 353,942
- 115
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- 851
9
votes
1 answer
Something about a completely empty class
#include
using namespace std;
class Empty{
char omg[0];
};
int main()
{
Empty em1, em2;
Empty set[100];
cout << sizeof(Empty) << " " << sizeof(em1) << " " << sizeof(em2) << endl;
cout << (long*)&em1 << " " <<…
simon_xia
- 2,394
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9
votes
4 answers
Generating empty objects - empty class with empty properties/subclasses C#
I have two classes:
public class HumanProperties { int prop1; int prop2; string name;}
public class Human{int age; HumanProperties properties;}
Now if i want to create new instance of Human, i have to do Human person = new Human();
But when i try…
Muno
- 749
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4
votes
2 answers
Why sizeof(Derived4) is 8 byte? I think it should be 5 bytes
This is the output of the given program:
sizeof(Empty) 1
sizeof(Derived1) 1
sizeof(Derived2) 4
sizeof(Derived3) 1
sizeof(Derived4) 8
sizeof(Dummy) 1
This is the program:
#include
using namespace std;
class Empty
{};
class Derived1 :…
Devesh Agrawal
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3
votes
1 answer
Is there something like is_empty_but_has_virtual_functions?
I would like to craft an "interface"/mix-in class (template), and ensure nobody thinks that adding a member to this class template is a good idea, I'd like to static_assert on this condition.
Unfortunately, std::is_empty does not allow virtual…
rubenvb
- 74,642
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3
votes
2 answers
Construct an empty object without the default constructor
Suppose I have a type F. I know that F is empty, but F has no default constructor, so I can't use F() to construct it. Is there a way to obtain a valid object of type F anyway? I seem to recall a mention that there was such a way with arcane usage…
Justin
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3
votes
1 answer
Chained inheritance of empty classes, still necessary?
Are there still good reasons to use chainned base cases rather than a flat multiple inheritance?
It used to be the case that some classes were designed to be inherted in chain. I think this was to force the empty base class optimization.
I…
alfC
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2
votes
1 answer
Do we ever need empty class in java project? If yes then why?
In empty class (without field and properties) also compiler automatically creates a default constructor after compiling. If we never use this empty class then why compiler creates this default constructor?
Raghunath
- 29
- 4
2
votes
1 answer
C++ Exceptions Throw Empty Class
Below is an excerpt from "Programming: Principles and Practice Using C++". I'm confused by the throw Bad_area() notation. The book tries to explain it, "Bad_area() means 'Make an object of type Bad_area'," continuing with that it then throws that…
Jay Adams
- 23
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1
vote
1 answer
Why c++ empty class have no byte alignment？
I recently learned that empty class have size 1 instead of zero.Why it has no byte alignment, in which
it's size should be 4 in 32bit environment? What's the address of the next object?
uuuvv
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