What is the (...) called in C and C++?

Question

One of the uses of ... is to denote variadic entities in C and C++.

What is its name?
Is it classified as an operator or something else when used that way?
Any other details regarding ...?

Edit: I know the purpose of .... I am asking about its name and classification, which I hope, is similar in C and C++.

Does this answer your question? In a C function declaration, what does "..." as the last parameter do? — Ajay Dabas
– Ajay Dabas, Commented Jan 11, 2020 at 17:53
C variadic functions and C++ variadic template arguments are completely different, can you give context in which you found it? (PS, C/C++ doesn't exist, please pick one) — JVApen
– JVApen, Commented Jan 11, 2020 at 17:57

dumbass · Accepted Answer · 2022-08-20 13:45:40Z

47

It is one of the punctuators.

6.4.6  Punctuators
Syntax punctuator:
     one of  [    ]    (    )    {   }    .    ->
             ++   --   &    *    +   -    ~    !
             /    %    <<   >>   <   >    <=   >=    ==   !=   ^   |   &&   ||
             ?    :    ;    ...
             =    *=   /=   %=   +=  -=   <<=  >>=   &=   ^=   |=
             ,    #    ##
             <:   :>   <%   %>   %:   %:%:

In the function declaration it is called the ellipsis.

Ellipsis is also used by some compiler C language extensions. Example - gcc switch/case range extension

const char *test(unsigned num)
{
    switch(num)
    {
        case 0 ... 9:
            return "the value is in the 0 to 9 range";
        case 10 ... 99:
            return "the value is in the 10 to 99 range";
        default:
            return "out of tested range";
    }
}

https://godbolt.org/z/YBLma-

edited Aug 20, 2022 at 13:45

dumbass

27.1k4 gold badges42 silver badges77 bronze badges

answered Jan 11, 2020 at 18:43

0___________

71.6k4 gold badges41 silver badges94 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Ardent Coder Over a year ago

However, as one of the comments in my question mentioned about parameter packs, why didn't you mention it in your answer?

pmg Over a year ago

Link to the C11 Standard: port70.net/~nsz/c/c11/n1570.html#6.4.6

Nicol Bolas Over a year ago

@ArdentCoder: It's still called an ellipsis in C++, even for parameter packs.

zwol Over a year ago

I would add that ... is not an operator, because it cannot form part of an expression (in the sense of 'expression' defined by C11 §6.5). It has more in common with { } and ; than with the other punctuators.

aschepler Over a year ago

@zwol In C++ the token ... can be part of an expression. But it's not considered an operator by the formal syntax.

|

Quuxplusone · Accepted Answer · 2020-01-12 17:35:29Z

14

The ... is referred to as an ellipsis both in English and in the C standard.

edited Jan 12, 2020 at 17:35

Quuxplusone

28.7k9 gold badges111 silver badges190 bronze badges

answered Jan 11, 2020 at 18:50

Ahmed Masud

22.7k3 gold badges37 silver badges60 bronze badges

Comments

score 7 · Accepted Answer · 2020-01-13 06:33:53Z

One of the uses of ... is to denote variadic entities in C and C++.`

Yes, In layman's terms ... can be thought of as denoting more than one or multiples (as in pseudo-code punctuation we sometimes use multiple dots to resemble different types) of a use case, for which if we consider variadics (being multiple in the sense of 'varying' arguments/parameters) in C++, it would refer to a variable number of arguments for functions or templates.

What is its name?

Ellipsis

Is it classified as an operator or something else when used in that way?

No, it's definitely not an operator as it allows you to pass any number of arguments, not operate on them.

Any other details regarding ...?

As far as I know -

Its a special specifier;
The ellipsis always comes last in the argument list;
As far as its usage is concerned, its only used when you want to remove the limits on the number of parameters for a template/function or when you require to have an extensible number of parameters for expansion. (i.e. it provides parameter pack expansion in a variadic class template or function template) In practice we mostly require a fixed set of known parameters, so it isn't applicable to most cases;
It can be used with sizeof operator, as it's classified as a pack expansion as well.

Edit: I know the purpose of ... I am asking about its name and classification, which I hope, is similar in both C and C++.

The name is same, but usage may vary for C++ and C.

Am only familiar with its use in the former language. (I remember having a HackerRank problem on Variadics, covering its utility.)

Andreas DM · Accepted Answer · 2020-01-12 17:56:07Z

4

The sequence of three full stops ... is called an ellipsis in both C and C++

In C++, the ellipsis helps initialize and expand different kinds of packs.

A parameter pack - when there is an ellipsis between the type and the identifier
Type ... identifier
A pack expansion - consists of a pattern and an ellipsis
pattern...

answered Jan 12, 2020 at 17:56

Andreas DM

11.1k6 gold badges39 silver badges67 bronze badges

Collectives™ on Stack Overflow

What is the (...) called in C and C++?

4 Answers 4

6 Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

6 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related