Where does the C standard define the else if statement?

Question

I was just curious about the else if statement in C so I looked at the C99 standard and found nothing. Then I looked at the grammar but again no else if

selection_statement
    : IF '(' expression ')' statement
    | IF '(' expression ')' statement ELSE statement
    | SWITCH '(' expression ')' statement
    ;

How is the else if declared in C. By reading the standard, how can I notice it is part of it?

The last `statement` in `IF '(' expression ')' statement ELSE statement` can be another `if` statement. — user2357112, Aug 27 '20 at 17:55
`else if` is a byproduct of an `if` statement being a statement. — Thomas Jager, Aug 27 '20 at 17:56
To clarify, there's nothing special about the `if` after an `else`. It's just another statement. — yhyrcanus, Aug 27 '20 at 17:57
Please see [Where do I find the current C or C++ standard documents?](https://stackoverflow.com/a/83763/) — Weather Vane, Aug 27 '20 at 18:07
[C2x draft](http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2478.pdf) in PDF format from [JTC1/SC22/WG14 - C](http://www.open-std.org/jtc1/sc22/wg14/) — pmg, Aug 27 '20 at 18:17
There is no `else if`. The code `if (x) { foo(); } else if (y) { bar(); }` is missing a set of braces. The compiler sees it as `if (x) { foo(); } else { if (y) { bar90; }}`. The `else if` shorthand is allowed because the braces are optional when the `else` is followed by a single statement. — user3386109, Aug 27 '20 at 18:44

score 3 · Answer 1 · answered Aug 27 '20 at 18:05

3

C 2018 6.8.4 says a selection-statement may be “if ( expression ) statement else statement”. C 2018 6.8 says that latter statement may be “selection-statement”, and so it may be an if or if … else statement, which results in a statement containing else if.

answered Aug 27 '20 at 18:05

Eric Postpischil

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It might help to point out that this would be different in a language where subclauses of control flow constructs had to be blocks. Nobody wants to write a long if-else chain like `if (expression) { statements; } else { if (expression2) { statements; } else { if (expression3) { statements; } else { ... } } }`. – zwol Aug 27 '20 at 18:52

RobertS supports Monica Cellio · Accepted Answer · 2020-08-27T19:18:46.860

The else if statement is officially defined as byproduct of the if statement in §6.8.4/1, C18 by declaring the syntax:

Syntax

1 selection-statement:

if ( expression ) statement

if ( expression ) statement else statement

Source: C18, §6.8.4/1

The last "statement" in the latter form describes that another if statement can be followed after an else.

Beside that, you can find an, of course non-normative, example of its use in the C standard in normative appendix G in the code example at G.5.1/8:

if (isnan(x) && isnan(y)) { ... }
else if ((isinf(a) ||isinf(b)) && isfinite(c) && isfinite(d)) { ... }
else if ((logbw == INFINITY) && isfinite(a) && isfinite(b)) { ... }

This is the only place where an else if statement appears as it is in the C18 standard.

So regarding:

By reading the standard, how can I notice it is part of it?

There at least although examples are non-normative it is part of it.

Where does the C standard define the else if statement?

2 Answers2