I am trying to figure out what order of evaluation is. I really don't understand point of order of evaluation. Evaluate it operands, subexpressions, expressions or what ?
I was trying to do some research and look at the difference between gcc and vc compiler, but after a lot of time spend on this research, I still don't understand what order of evaluation does.
Let's take an example:
-----------------First example-----------------
int i = 1, j;
j = (i = 5) + (i = 6);
gcc and visual studio result: j = 12
How I think order of evaluation works here (looks like left to right):
First is evaluated operand j -> there is some random number in this variable.
j = (i = 5) + (i = 6);Then is evaluated operand i -> i (with value 1)
j = (i = 5) + (i = 6);Then is evaluated constant 5 -> 5
j = (i = 5) + (i = 6);Then is evaluated whole subexpression (i = 5) -> i (with value 5)
j = (i) + (i = 6);Then is evaluated operand i -> i (with value 5)
j = (i) + (i = 6);Then is evaluated constant 6 -> 6
j = (i) + (i = 6);Then is evaluated whole subexpression (i = 6) -> i (with value 6)
j = (i) + (i);After all order of evaluation, here comes precedence and associativity and everything calculates.
(j = ((i) + (i)));->(j = ((6) + (6)));->j = 12
-----------------Second example-----------------
int x = 1, y = 2, z = 5;
x = (y = 3, (z = ++y + 2) + 5);
gcc and visual studio result: x = 11
How I think order of evaluation works here (looks like left to right):
First is evaluated operand x -> x (with value 1)
x = (y = 3, (z = ++y + 2) + 5);- Then should be evaluated subexpression
(y = 3, (z = ++y + 2) + 5). Also comma saysy = 3must be evaluated before(z = ++y + 2) + 5 So then is evaluated operand is y -> y (with value 2)
x = (y = 3, (z = ++y + 2) + 5);Then evaluated is constant 3 -> 3
x = (y = 3, (z = ++y + 2) + 5);Then evaluated is whole subexpression (y = 3) -> y (with value 3)
x = (y, (z = ++y + 2) + 5);!!!This is pretty weird, because according to example y = 3 is not subexpressionThen evaluated is operand z -> z (with value 5)
x = (y, (z = ++y + 2) + 5);Then evaluated is operand (or subexpression, IDK what it is) ++y -> y (with value 4)
x = (y, (z = ++y + 2) + 5);Then evaluated is constant 2 -> 2
x = (y, (z = ++y + 2) + 5);Then evaluated is whole subexpression (z = ++y + 2) -> z (with value 6)
x = (y, (z) + 5);Then evaluated is constant 5 -> 5
x = (y, (z) + 5);Then evaluated is whole subexpression (y = 3, (z = ++y + 2) + 5) -> 11
x = (11);After all order of evaluation, here comes precedence and associativity and everything calculates.
(x = (11)); -> x = 11
-----------------Third example-----------------
int x = 1, y = 2, z = 5;
x = (y = 3) + (y = 3) + (y = 5);
gcc result: x = 11
visual studio result: x = 15
This "explanation" of this example will be fast....
How I think order of evaluation works here for gcc (looks like left to right):
I think gcc save value instead of variable, but why?????
x = (y = 3) + (y = 3) + (y = 5); x = (3) + (3) + (5); //saves value instead of variable????? x = 15
How I think order of evaluation works here for visual studio (looks like left to right):
x = (y = 3) + (y = 3) + (y = 5); x = (y) + (y) + (y); //Last value of y was 5, so...... x = 5 + 5 + 5 x = 15
So everything confuses me and this is just really bad research cause I don't understand it.
So I ask you:
What order of evaluation does ? Does operands, subexpressions, expressions or what ? If all, is operand evaluated before subexpression and subexpression before expression ?
Is order of evaluation related to precedence and associativity (maybe for some compilers)
Is order of evaluation done before or after precedence and associativity ?
Why sometimes (like in third example) it looks like compiler saves value instead of variable ? Also this can be wrong cause it can save something completely different, lol....
According to me, I completely wrong what I wrote up - it doesn't make any sense.
Thank you in advance for your answers
