cout prints wrong data with ++ and -- operator

Asked Nov 14 '16 at 20:52

Active Nov 14 '16 at 20:52

Viewed 43 times

one of my friends asked me a question about ++ and -- operators and printing an int with cout . In his example he used kinda this code(I changed code in order to be readable):

#include <iostream>
using namespace std;
int main()
{
   int  a=5;
   cout<<a<<a++<a;
}

and the output was this:

Why is that and what causes this ? It should print 556 .And also it happens with -- operator too

asked Nov 14 '16 at 20:52

ali73

*"It should print 556"*. Should it? Where did you read the evaluation order of function parameters is specified like that? – StoryTeller - Unslander Monica Nov 14 '16 at 20:53
https://www.tutorialspoint.com/cplusplus/cpp_increment_decrement_operators.htm this is a link but im looking into my books – ali73 Nov 14 '16 at 21:19
c++ how to program 8th edition by deitel & deitel chapter 4 fig.4.18 – ali73 Nov 14 '16 at 21:21
You didn't read there that `a` will be evaluated first, then `a++` and finally `a`. The evaluation order of function arguments (`operator<<` is a function here, applied multiple times) is undefined. – StoryTeller - Unslander Monica Nov 14 '16 at 21:23
excuse me but what do you mean by "undefined"? – ali73 Nov 14 '16 at 21:30
I mean the c++ standard explicitly says it's undefined. It doesn't impose an order, so 556 is just as valid as 656. And it's completely up to the implementation of your compiler. – StoryTeller - Unslander Monica Nov 14 '16 at 21:35
But we call "< – ali73 Nov 14 '16 at 21:39
1

@StoryTeller actually the evaluation order of operands is unspecified – M.M Nov 14 '16 at 21:51
@M.M Yes, I know the standard uses *undefined* and *unspecified* to mean to different things. But alas, my memory always fails me when it's time to be precise :) – StoryTeller - Unslander Monica Nov 15 '16 at 06:22

cout prints wrong data with ++ and -- operator

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