Creating struct variable using the tag name

Question

I have read a article in the following link

http://www.embedded.com/electronics-blogs/programming-pointers/4024450/Tag-vs-Type-Names

Here author says that, use of follwing is wrong.

struct s
{
--
};

s var;

But in my sample code its works perfectly.

  1 #include<iostream>
  2 using namespace std;
  3
  4 struct s
  5 {
  6    int sd;
  7 };
  8 s v;
  9
 10
 11
 12 int main()
 13 {
 14
 15    v.sd=10;
 16    cout<<v.sd;
 17    return 0;
 18 }

EDIT:

What the actual difference? why it works in c++ and not works in c;

Answer 1

It is the difference between C++ and C. The author you are citing speaks about C while you use C++ code instead of C code. In C you have to specify keyword struct, union or enum before declaring variables of correspondings types.

Answer 2

The article says that a user-defined type using

struct s {
   ...
};

defines a tag name s. To name the actual type, you can write struct s (C or C++) or class s (C++ only), but C++ makes both keywords optional (and almost never actually used). So whenever you write s in C++ it's actually interpreted as the correct type, while in C the keyword is obligatory to name the type.

So long story short: in C++ there is no difference in writing struct s, class s or s, they all mean the same.

In order to define the type name s in a C/C++ shared header, one typically writes

typedef struct {
   ...
} s;

Then the type s can be used in both C and C++ without the need to write struct.