On topic The comma operator will always yield the last value in the comma separated list. Basically it’s a binary operator that evaluates the left hand value but discards it, then evaluates the right hand value and returns it. If you chain multiple of these they will eventually yield the last value in the chain. … Read more
I believe behavior is well-defined because of 8[dcl.decl]/3 Each init-declarator in a declaration is analyzed separately as if it was in a declaration by itself. Which is even additionally explained in a footnote as A declaration with several declarators is usually equivalent to the corresponding sequence of declarations each with a single declarator. That is … Read more
var c = (a,b); The above uses the comma operator. It evaluates as the value of its right-hand side (i.e. b). var c = a,b; This does not use the comma operator. The comma character here forms part of the var expression which takes a comma-separated list of variables to create in the current scope, … Read more
The , operator evaluates a series of expressions and returns the value of the last. c=a,b is the same as (c=a),b. That is why c is 10 c=(a,b) will assign the result of a,b, which is 20, to c. As Mike points out in the comments, assignment (=) has higher precedence than comma
The first one is equivalent to: (true ? (++x, ++y) : (–x)), –y; The second one is equivalent to: (false ? (++x, ++y) : (–x)), –y; Thus the –y is always executed. In the first line, the increments are executed first so x = 1, y = 0 is expected. In the second line, the … Read more
A common idiom is to use the comma operator which evaluates both operands, and returns the second operand. Thus: for(int i = 0; i != 5; ++i,++j) do_something(i,j); But is it really a comma operator? Now having wrote that, a commenter suggested it was actually some special syntactic sugar in the for statement, and not … Read more
In your example it serves no reason at all. It is on occasion useful when written as if(cond) perror(“an error occured”), exit(1) ; — then you don’t need curly braces. But it’s an invitation to disaster. The comma operator is to put two or more expressions in a position where the reference only allows one. … Read more
In the expression (i, ++i, 1), the comma used is the comma operator the comma operator (represented by the token ,) is a binary operator that evaluates its first operand and discards the result, and then evaluates the second operand and returns this value (and type). Because it discards its first operand, it is generally … Read more
The comma operator evaluates both of its operands (from left to right) and returns the value of the second operand. Source: https://developer.mozilla.org/en/JavaScript/Reference/Operators/Special_Operators/Comma_Operator For example, the expression 1,2,3,4,5 evaluates to 5. Obviously the comma operator is useful only for operations with side-effects. console.log(1,2,3,4,5); console.log((1,2,3,4,5));
Section 6.6/3, “Constant expressions”, of the ISO C99 standard is the section you need. It states: Constant expressions shall not contain assignment, increment, decrement, function-call, or comma operators, except when they are contained within a subexpression that is not evaluated. In the C99 rationale document from ISO, there’s this little snippet: An integer constant expression … Read more