What is the difference between struct in c and c plus plus?

Answer 1

In C, a struct is simply a type that can hold several sub-objects.

In C++, struct is almost the same as "class". It can have member functions, parent structs and classes, etc. The only difference between struct and class is that the members of class are by default private, while the members of struct are by default public. Thus, a standard C struct is also a good C++ struct - simply one that has no member functions and no parents.

Answer 2

The internal members of a struct are the same for both C and C++. However, a C struct has no member methods and is entirely public. A C++ struct, on the other hand, is public by default but otherwise works exactly the same as a class.

Aside from object-oriented nature of the C++ struct, the major difference between the two is in the declaration.In C, you could declare a struct in a variety of ways:

1. struct foo {...}; struct foo bar;
2. struct foo {...} bar;
3. typedef struct foo {...} bar;

The above three lines are all functionally equivalent (although you can't use all three in the same namespace, of course). However, the explicit use of typedef is the preferred method in C, thus allowing new instances of the structure to be created without the need to continually use the struct keyword:

typedef struct foo {...} bar;
foo another_bar;
foo yet_another_bar;

In C++ the use of typedef is not necessary, so the declarations can use the more simplified form:

struct foo {...} bar;
foo another_bar;
foo yet_another_bar;

Note that typedef is not implied, it's simply not required. You can still use a typedef if you want, but it's existence is mostly for backward compatibility with C. In fact, the only time a typedef is ever required is when the tag name or instance name clash with a function name in the same namespace. Although its ultimately better to avoid name clashes altogether, a typedef will resolve the clash.

Answer 3

A struct in C is simply a data record, much like a database record but with member variables instead of fields. They essentially allow a group of related datums to be treated as a single entity. They are often used as the return value from a function because a function can only return a single value. By returning a struct a function can effectively return several values at once. Functions can also be overloaded to either accept multiple parameters or a single struct. Structs also make it possible to implement more complex data structures, such as linked lists and trees.

A struct in C++ is exactly the same as a class in C++. The only real difference between the two is that struct members are public by default, whilst class members are private by default. Other than that, anything you can do with a class you can also do with a struct. However, most C++ programmers use them exactly as they would in C (with no member methods and a purely-public interface to the member variables), and derive a class from a struct whenever they need to instantiate full-blown objects from the struct. This convention is common within Microsoft Windows software, where a CRect class is derived from a RECT struct. While this convention allows far greater interoperability with C programs, it's hard to justify the use of non-encapsulated structs within an object-oriented programming environment, especially when you are then forced to provide two separate implementations to cater for what is essentially the same data type.

Answer 4

In C a struct is used to define a "plain old data" structure (a POD) but in C++ a struct is simply an alternative way of defining a class. That is, the struct and class keywords are interchangeable in C++. The only real difference is that struct members are public by default while class members are private by default. As such, the following declarations are equivalent:

// C or C++

struct X {

int data; // public access by default

};

// C++ only

class X {

public:

int data; // explicitly public

};

The same applies to inheritance in C++. A struct uses public inheritance by default while a class uses private inheritance by default. Given the following base class...

// C or C++

struct B {/*...*/};

...the following definitions are equivalent:

// C++ only

struct D : B {/* ...*/ }; // Public inheritance by default

class D : public B {/* .... */}; // Explicit public inheritance

By convention we use a struct in C++ just as we would a struct in C, to store plain old data that is publicly accessible, requires trivial construction and is compliant with C code. For example:

// C and C++

struct Point {

int x;

int y;

};

This structure has no invariant (all integer values are valid for both x and y) so there's really no need for any unnecessary constructors or assignment operator overloads. The structure supports trivial construction and member-wise initialisation in C++, just as it does in C.

Answer 5

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Answer 6

There is no difference. C and C are the same language.