C C Struct vs Class

Question

After finishing my C   class it seemed to me the structs classes are virtually identical except with a few minor differences   I ve never programmed in C before  but I do know that it has structs  In C is it possible to inherit other structs and set a modifier of public private   If you can do this in regular C why in the world do we need C    What makes classes different from a struct

User · Answer

It s not possible to define member functions or derive structs from each other in C    Also  C   is not only C    derive structs   Templates  references  user defined namespaces and operator overloading all do not exist in C

User · Answer

C   uses structs primarily for 1  backwards compatibility with C and 2  POD types   C structs do not have methods  inheritance or visibility

User · Answer

I m going to add to the existing answers because modern C   is now a thing and official Core Guidelines have been created to help with questions such as these   Here s a relevant section from the guidelines      C 2  Use class if the class has an invariant  use struct if the data members can vary independently      An invariant is a logical condition for the members of an object that a constructor must establish for the public member functions to assume  After the invariant is established  typically by a constructor  every member function can be called for the object  An invariant can be stated informally  e g   in a comment  or more formally using Expects       If all data members can vary independently of each other  no invariant is possible       If a class has any private data  a user cannot completely initialize an object without the use of a constructor  Hence  the class definer will provide a constructor and must specify its meaning  This effectively means the definer need to define an invariant       Enforcement      Look for structs with all data private and classes with public members    The code examples given   struct Pair       the members can vary independently     string name      int volume         but  class Date   public         validate that  yy  mm  dd  is a valid date and initialize     Date int yy  Month mm  char dd              private      int y      Month m      char d        day      Classes work well for members that are  for example  derived from each other or interrelated  They can also help with sanity checking upon instantiation  Structs work well for having  bags of data   where nothing special is really going on but the members logically make sense being grouped together   From this  it makes sense that classes exist to support encapsulation and other related coding concepts  that structs are simply not very useful for

User · Answer

In C    structs and classes are pretty much the same  the only difference is that where access modifiers  for member variables  methods  and base classes  in classes default to private  access modifiers in structs default to public   However  in C  a struct is just an aggregate collection of  public  data  and has no other class-like features  no methods  no constructor  no base classes  etc   Although C   inherited the keyword  it extended the semantics    This  however  is why things default to public in structs   a struct written like a C struct behaves like one    While it s possible to fake some OOP in C mdash for instance  defining functions which all take a pointer to a struct as their first parameter  or occasionally coercing structs with the same first few fields to be  sub superclasses    it s always sort of bolted on  and isn t really part of the language

User · Answer

Other that the differences in the default access  public private   there is no difference    However  some shops that code in C and C   will use  class struct  to indicate that which can be used in C and C    struct  and which are C   only  class   In other words  in this style all structs must work with C and C    This is kind of why there was a difference in the first place long ago  back when C   was still known as  C with Classes     Note that C unions work with C    but not the other way around  For example  union WorksWithCppOnly      WorksWithCppOnly   a 0        friend class FloatAccessor      int a  private      float b       And likewise   typedef union friend      int a      float b    class    only works in C

User · Answer

One more difference in C    when you inherit a class from struct without any access specifier  it become public inheritance where as in case of class it s private inheritance

[c++] C/C++ Struct vs Class

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