What is the use of structure having only one element?

Question

Example:

struct dummy 
{
    int var;
};

Why structures like this are used? Mostly I have seen them in some header files.

The atomic_t type is also defined like this. Can't it be defined simply using:

typedef int atomic_t;

Answer 1

Besides extensibility, this idiom also makes it syntactically impossible to do normal arithmetic on types whose meaning is such that that doesn’t make sense semantically.

E.g.:

typedef uint32_t myObject;
myObject x, y;
...
y = x + 3; // meaningless, but doesn’t produce an error.
           // may later cause runtime failure.

v.s.

typedef struct { uint32_t var; } myObject;
myObject x, y;
...
y = x + 3; // syntax error.

This may seem contrived, but it is occasionally very useful.