sizeof(EmptyStruct) in C and C++ (was: Base {}; sizeof(Base) == 1?)

[Alex Vinokur]

* (e-mail address removed):

This may be stupid question, but why is sizeof(Base) == 1 in:

int main(int argc, char* argv[])
{
class Base
{
};
cout << sizeof(Base) << endl;
return 0;
}

I guess I want to know what the 1 byte is for? There is no vptr here,
so why 1 byte?I checked FAQ and couldn't find answer.

Needs a unique address.

struct Empty {};

C: sizeof(Empty) == 0
C++: sizeof(Empty) > 0

Why doesn't C need a unique address?

 

[Keith Thompson]

* (e-mail address removed):

This may be stupid question, but why is sizeof(Base) == 1 in:

int main(int argc, char* argv[])
{
class Base
{
};
cout << sizeof(Base) << endl;
return 0;
}

I guess I want to know what the 1 byte is for? There is no vptr here,
so why 1 byte?I checked FAQ and couldn't find answer.

Needs a unique address.

struct Empty {};

C: sizeof(Empty) == 0
C++: sizeof(Empty) > 0

Why doesn't C need a unique address?

In C,
struct Empty {};

is a syntax error. (Some compilers might support that as an
extension; if so, it's up to the compiler to decide what
sizeof(struct Empty) should be.)

 

[swets]

* (e-mail address removed):
This may be stupid question, but why is sizeof(Base) == 1 in:

int main(int argc, char* argv[])
{
class Base
{
};
cout << sizeof(Base) << endl;
return 0;
}

I guess I want to know what the 1 byte is for? There is no vptr here,
so why 1 byte?I checked FAQ and couldn't find answer.

Needs a unique address.

struct Empty {};

C: sizeof(Empty) == 0
C++: sizeof(Empty) > 0

Why doesn't C need a unique address?

In C,
struct Empty {};

is a syntax error. (Some compilers might support that as an
extension; if so, it's up to the compiler to decide what
sizeof(struct Empty) should be.)

What is the size of a in
int a[0];

 

[Igmar Palsenberg]

What is the size of a in
int a[0];

A zero size array is illegal according to ANSI C.


Igmar

 

[Sweta]

What if I use it in a structure like -
struct A {
int a[0];
};

What is the size of such structure?

Thanks,
Sweta

What is the size of a in
int a[0];

A zero size array is illegal according to ANSI C.


Igmar

 

[Hallvard B Furuseth]

What if I use it in a structure like -
struct A {
int a[0];
};

What is the size of such structure?

Still not valid. Standard C does not allow 0-sized objects - and that
includes objects that are part of other objects.

 

[Igmar Palsenberg]

What if I use it in a structure like -
struct A {
int a[0];
};

What is the size of such structure?

What isn't clear about 'a zero size array is illegal' ? Putting it in a
doesn't make it less of an array.


Igmar

 

[Clark S. Cox III]

What is the size of a in
int a[0];

A zero size array is illegal according to ANSI C.

What if I use it in a structure like -
struct A {
int a[0];
};

What is the size of such structure?

As Igmar said, "A zero size array is illegal according to ANSI C."