Thread: comma operator clarification

You can't declare more than one type in the same statement. If the variables are of the same type, just separate them by commas. If the variables are of different type, declare them in separate statements, like:

Code:

int i;
char c;

and

Code:

int i, j;

Originally Posted by GReaper

You can't declare more than one type in the same statement.

That's not true. A compound statement (which is what you get when you place a bunch of declarations and statements within curly braces to form a block) can contain multiple declarations (of both types and variables) as well as other statements. Most other statements can't include any declarations.

In any event.....

I don't have a copy of the 2011 standard handy, but the relevant section of the 1999 standard is 6.7. As Hodor said, this is not a usage of the comma operator. Declarations are composed of a single declaration specifier (which specifies types, storage class, etc) and a list of one or more declarators separated by commas (where each declarator includes an identifier - the name of something being declared).

In a declaration

Code:

    int i, j;

the "int" is the declaration specifier, and i and j are both the names of things being declared (i.e. the declarators).

Whereas, the (incorrect) declaration

Code:

    int i, char c;

is invalid because "int" and "char" are both declaration specifiers.

Originally Posted by grumpy

That's not true. A compound statement (which is what you get when you place a bunch of declarations and statements within curly braces to form a block) can contain multiple declarations (of both types and variables) as well as other statements. Most other statements can't include any declarations

Oh, I see! I didn't have compound statements in mind, though.