The comma operator has the lowest precedence of all C/C++ operators. Therefore it’s always the last one to bind to an expression, meaning this: a = b, c; is equivalent to: (a = b), c; Another interesting fact is that the comma operator introduces a sequence point. This means that the expression: a+b, c(), d … Read more
The statement return (x = x + 2, x + 1); is equivalent to: x = x + 2; // x == 7 return x + 1; // returns 8
In C, comma operator doesn’t produce an lvalue, consequently the array arr which is an lvalue decays into a pointer type which is a rvalue (in this case). So sizeof(0,arr) becomes equivalent to sizeof(char*), due to lvalue-to-rvalue conversion. But in C++, comma operator produces an lvalue. There is no lvalue-to-rvalue conversion. So sizeof(0,arr) remains same, … Read more
Can any one explain how output is 2? Because the precedence of the assignment operator (=) is higher than the comma operator (,). Therefore, the statement: a = (1, 2), 3; is equivalent to: (a = (1, 2)), 3; and the expression (1, 2) evaluates to 2.
Look at the grammar for the C language. It’s listed, in full, in Appendix A of the standard. The way it works is that you can step through each token in a C program and match them up with the next item in the grammar. At each step you have only a limited number of … Read more
Comma operator is applied and the value 5 is used to determine the conditional’s true/false. It will execute blah() and get something back (presumably), then the comma operator is employed and 5 will be the only thing that is used to determine the true/false value for the expression. Note that the , operator could be … Read more
That’s because return and break are statements, not expressions. As such, you cannot use it in another expression in any way. if and the others are similarly also statements. What you can do however is rewrite your expression (for return) so that it’s not nested in an expression – not that I recommend writing code … Read more
According to the C FAQ: Precisely stated, the meaning of the comma operator in the general expression e1 , e2 is “evaluate the subexpression e1, then evaluate e2; the value of the expression is the value of e2.” Therefore, e1 had better involve an assignment or an increment ++ or decrement — or function call … 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
According to the Operator Precedence, comma operator has lower precedence than operator=, so x = 2,3; is equivalent to (x = 2),3;. (Operator precedence determines how operator will be bound to its arguments, tighter or looser than other operators according to their precedences.) Note the comma expression is (x = 2),3 here, not 2,3. x … Read more