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What are the differences between struct and class in C++
C++ - struct vs. class
How are structures different from objects and classes in C++? Is there any performance benefit to using objects or structures?
Structures and classes are identical; the language standard uses the term "class" to refer to both. The only difference between defining a class using the struct or the class keyword is the default accessibility of members and base classes; there is no difference in their runtime behaviour or performance.
An "object" is a run-time instance of a type. In C++, the term is used for instances of any type, including classes and fundamental types.
main thing is by default variables are private in a class and by default they are public in structures. also you can google this and find a million and one topics on this. for example http://blog.stevedoria.net/20050913/differences-between-cpp-classes-and-structs
Related
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When should you use a class vs a struct in C++? [duplicate]
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Closed 4 years ago.
Suppose you have to develop an application for XYZ bank with the following features.
1)The application must be secure
2)For transactions, proper interfaces will be provided to the customers.
3)The application must be reusable.
4)The application must be efficient in terms of speed and memory usage.
You can use either structs or class in order to achieve the above mentioned features. So which programming construct (class or struct) will you select for application development.
Please help me out here. Thanks
struct and class are nearly equivalent in C++ (you can have member functions, constructors & destructors, data members in both). More precisely,
struct Sometype {
/// some code here
};
is equivalent to
class Sometype {
public:
/// some code here
};
So the runtime efficiency is the same (since public: is an annotation for the compiler which is lost, as most type information, at runtime; be aware of type erasure).
You really should take days to read some good book about C++ programming, then look into some C++ reference site, then read (or at least refer to) some C++ standard like n3337 (for C++11; for later standards, find them by yourself).
Learn about the rule of five and about standard containers and smart pointers.
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What are the differences between struct and class in C++?
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Closed 8 years ago.
Is the size of a struct and the size of the equivalent class guaranteed to be equal?
Essentially struct and class are identical in C++, with 2 differences:
Members of a struct are public by default, while in a class they're private. Access modifiers still apply when supplied by the programmer.
When deriving a struct from a class or struct, the default access modifier for the base is public. And when deriving a class, the default access is private.
In general, programmers assume that in a struct all members are public and freely modifiable, and in a class they will all be private and getters/setters will be present as appropriate. This is merely convention though and not enforced by the language.
Since they are treated identically by the compiler apart from the default access, sizes are guaranteed to be identical. The main reason that both keywords are historically supported by C++, even though slightly redundant, is backwards compatibility with C where only struct exists.
Assuming you're asking about CPP.
Members of a struct are public by default.
In a class, they default to private.
struct and class are otherwise functionally equivalent.
structs are typically used as open data containers.
The size of a class and structure will tend to be the same given that the ordering of its data members are in the same order and you did not change the default member alignment.
This question already has answers here:
When should you use a class vs a struct in C++? [duplicate]
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C++ - struct vs. class [duplicate]
(5 answers)
Closed 9 years ago.
When do we need to use a structure in a pure C++ program? Is structure at all required in a pure C++ program?
I understand that structure is the only way in a C program to encapsulate members and function pointers. But, if I use C++ to code my complete module, is it 100% alright if I stay away from structures and use a Class instead? Am I missing something?
(I googled but my question is very specific - is structure useless in pure C++ code)
=== EDITED ===
My question is not about the difference or commonalities between a structure and a class, but, do we need "struct" at all in C++, when you can 100% do away with a class. Is structure not redundant construct in C++, except for backward compatibility with C? I understand the difference between them w.r.t. the access specifiers but there are only syntactic differences.
The struct has been kept in C++ for backward compatibility with C. By default the struct members are public but the class members are private. You can replace class and struct with each other and get the same result if the type of members are pre-defined.
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Performances of Structs vs Classes
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Closed 9 years ago.
I was wondering if there is a difference in the running time of accessing data from a Struct and accessing data from an Class in C++. In my current understanding, a Struct is a class but with no member functions. I have some code which runs much more slowly with objects than with structs, which seems to suggest that there is a difference, but this confuses me as my intuition tells me that there shouldnt be a large difference.
As per " What are the differences between struct and class in C++? ", quoting from C++ FAQ
struct and class are otherwise functionally equivalent
(aside from minor private/public/protected defaults).
So there's no difference.
It is all the same, whether it is a struct or a class (I assume that it what you mean by object, since any instance is technically an object, be that a primitive, a struct or a class), the compiler does the same offset calculation to access members. There isn't really that much of a difference between the two - they may look different in terms of syntax, but the C++ call someObject.someMethod() is equivalent to the C version SomeObject_someMethod(&someObject) which is what a member call really is under the table. But this only concerns member methods, the access speed to members of classes and structs is practically identical.
I don't know why you would have that problem of different running times.
Structs and Classes, I'm assuming thats what you mean by objects, are virtually the same other than structs defaulting to public and classes defaulting to private.
So to sum it up there should be no difference functionally or speed wise
EDIT: the reason you may be experiencing structs running faster is because people tend to use structs for POD's whereas classes have more functionality, however this is based on style not actual the functionality of structs and classes
At runtime execution there is no difference in speed of execution.
you can refer similar threads.
Performances of Structs vs Classes
Class vs Struct for data only?
in C++ there are 3 kind of objects that belong to the class type:
struct
class
unions
they are functionally equivalent to each other, so you should expand more and tell more about your implementation.
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What are the differences between struct and class in C++
I've done my homework and had diverse answers on Google.
Some say structs do not have inheritance, some say structs do not have access specifiers, while others say they have both.
Could someone clarify then, the differences between a struct and a class in C and C++, and also the difference between a struct in C & C++.
In C++, the only difference between a struct and a class is that struct members are public by default, and class members are private by default.
However, as a matter of style, it's best to use the struct keyword for something that could reasonably be a struct in C (more or less POD types), and the class keyword if it uses C++-specific features such as inheritance and member functions.
C does not have classes.
C structs cannot use C++-specific features.
EDIT:
The C++ FAQ Lite, question 7.9, has this to say:
The members and base classes of a struct are public by default,
while in class, they default to private. Note: you should make
your base classes explicitly public, private, or protected,
rather than relying on the defaults.
struct and class are otherwise functionally equivalent.
OK, enough of that squeaky clean techno talk. Emotionally, most
developers make a strong distinction between a class and a struct.
A struct simply feels like an open pile of bits with very little
in the way of encapsulation or functionality. A class feels like a
living and responsible member of society with intelligent services, a
strong encapsulation barrier, and a well defined interface. Since
that's the connotation most people already have, you should probably
use the struct keyword if you have a class that has very few methods
and has public data (such things do exist in well designed
systems!), but otherwise you should probably use the class keyword.
And quoting Stroustrup's "The C++ Programming Language", 4th edition, section 16.2.4:
These two definitions of S are interchangeable, though it is
usually wise to stick to one style. Which style you use depends on
circumstances and taste. I tend to use struct for classes that I
think of as "just simple data structures." If I think of a class as "a
proper type with an invariant," I use class. Constructors and
access functions can be quite useful even for *struct*s, but as a
shorthand rather than guarantors of invariants.
In C, classes do not exist. In C++, structs have a default access specifier of public, while classes default to private.
There are several differences between structs in C and C++; in C++ they can inherit from other classes or structs, they can contain member functions, and their names don't need to be referred to with an elaborated type specifier.