Declaring structs vs. classes

[Markus Svilans]

Hi,

What is the difference between having a struct with constructors and
methods versus a class?

In many C++ examples online I have seen code similar to this:

struct Animal
{
Animal()
{
id = 0;
name[0] = 0;
}
int id;
char name[30];
};

Intuitively, I would understand structs with methods to be more data
oriented (i.e. no virtual methods), where the methods provide
initialization and maybe get/set methods. Classes would be more object
oriented, with more elaborate code, besides simple initialization and
get/set methods.

Can any one elaborate more on this? I'd like to understand better when
it's more correct to use a struct with methods, and when it's more
correct to use classes. Until now I have been using classes for any
kind of data structure that requires methods and automatic
initialization.

Thanks,
Markus.

 

[Noah Roberts]

Hi,

What is the difference between having a struct with constructors and
methods versus a class?

Default access permissions. Structs are public, classes are private.

struct X { int x; };
class Y { int y; };


X x;
Y y;

x.x = 5; // legal
y.y = 5; // illegal - no access to private member..

That is it...there is no other difference.

 

[Victor Bazarov]

What is the difference between having a struct with constructors and
methods versus a class?

[...]

FAQ 7.8

V

 

[mlimber]

Default access permissions. Structs are public, classes are private.

struct X { int x; };
class Y { int y; };


X x;
Y y;

x.x = 5; // legal
y.y = 5; // illegal - no access to private member..

That is it...there is no other difference.

Incorrect. Classes also default to private inheritance, while structs
default to public. The FAQ omits this part also, but it includes an
extra bit about idiomatic usage:

http://www.parashift.com/c++-faq-lite/classes-and-objects.html#faq-7.8

Cheers! --M

 

[osmium]

What is the difference between having a struct with constructors and
methods versus a class?

In many C++ examples online I have seen code similar to this:

struct Animal
{
Animal()
{
id = 0;
name[0] = 0;
}
int id;
char name[30];
};

Intuitively, I would understand structs with methods to be more data
oriented (i.e. no virtual methods), where the methods provide
initialization and maybe get/set methods. Classes would be more object
oriented, with more elaborate code, besides simple initialization and
get/set methods.

Can any one elaborate more on this? I'd like to understand better when
it's more correct to use a struct with methods, and when it's more
correct to use classes. Until now I have been using classes for any
kind of data structure that requires methods and automatic
initialization.

I see no point to the sample you posted. The fact that he uses a C style
string makes me wonder about how serious the programmer was.

From what you say, I think your understanding of the situation is pretty
much correct.

 

[mlimber]

Classes also default to private inheritance, while structs
default to public. The FAQ omits this part also,

.... uh, nevermind about that omission. It's there, I just missed it. --M

 

[Markus Svilans]

I see no point to the sample you posted. The fact that he uses a C style
string makes me wonder about how serious the programmer was.

I apologize for appearing non-serious through my use of inappropriate
example code.

Regards,
Markus.

 

[Markus Svilans]

Victor, thank you for pointing me at the FAQ. Very, very helpful.

Regards,
Markus.