C++ - Why an empty Structure will occupy 2Bytes in C++

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Why an empty Structure will occupy 2Bytes in C++

Total Answers and Comments: 5

Last Update: August 11, 2009 Asked by: pushpakumar

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Submitted by: mucdull

Because the class has no members (especially no virtual functions) its objects naturally should have 0 bytes. However the objects must be legally creatable because the class is not abstract (having no pure virtual functions) so there must be a way to address the objects. You cannot address something that does not take up any memory. Since the smallest addressable space is 1 byte, the compiler allocates 1 byte for the objects so to make them addressable.

To dwell on the topic, what do you think is the size of objects of this class?

class C { virtual void Go() {} };

Above answer was rated as good by the following members:
j_l_larson

September 26, 2007 10:55:17

sukhvir

RE: Why an empty Structure will occupy 2Bytes in C++

Size of empty structure in C++ is 1 byte because compiler assign 1 byte for structure name.

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November 16, 2008 02:37:46

mucdull

Member Since: November 2008 Contribution: 6

RE: Why an empty Structure will occupy 2Bytes in C++

Because the class has no members (especially no virtual functions) its objects naturally should have 0 bytes. However the objects must be legally creatable because the class is not abstract (having no pure virtual functions) so there must be a way to address the objects. You cannot address something that does not take up any memory. Since the smallest addressable space is 1 byte the compiler allocates 1 byte for the objects so to make them addressable.

To dwell on the topic what do you think is the size of objects of this class?

class C { virtual void Go() {} };

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1 0

Overall Rating: +1

February 18, 2009 03:45:59

santhosh.kanchanapally

Member Since: April 2008 Contribution: 10

RE: Why an empty Structure will occupy 2Bytes in C++

struct Emp
{
};

int _tmain(int argc _TCHAR* argv[])
{
cout<<"The size of structure is :"<<sizeof(Emp);
getchar();
return 0;
}

output::
The size of structure is : 1

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February 18, 2009 03:46:47

santhosh.kanchanapally

Member Since: April 2008 Contribution: 10

RE: Why an empty Structure will occupy 2Bytes in C++

Hence the size of an empty structure is 1 byte

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August 08, 2009 20:54:35

dkuy1

Member Since: August 2009 Contribution: 1

RE: Why an empty Structure will occupy 2Bytes in C++

The Standard C++ language definition says:

A class with an empty sequence of members and base class objects is an empty
class. Complete objects and member sub-objects of an empty class type shall have
nonzero size.

Most compiler give a size of 1.

cantrip . org/emptyopt . html This link explains in great detail why this is
and when it can have a different size if use as part of a class or struct:

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