weird behavior of algbraic evaluation in concatenated operators

[dejan budimir]

hi there!

#include <iostream>
using namespace std;

void main(){

int i=0,
j=10;

//Case one (the 'common' case):
cout<< "i == " << i << endl
<< "j == " << j << endl;

//Case two (the 'oddity'):
//Should print 1 and 11 (but will not evaluate the former expression
// before the latter, although it is printing in the correct order.
cout<< "(i+=1) == " <<(i+=1)<< endl
<< "(j+=i) == " <<(j+=i)<< endl;
}

The ostream's operator<<() method is defined as to be passed only two
arguments a time, one of which must be the class, which is being
returned to allow concatenation.

(cout<<expr1)<<expr2;

But it seems as if the whole set of expressions is being evaluated,
_before_ becoming the arguments of the operator methods and, in
addition, is being evaluated from the right to the left (from the
stack?).

Is this a microsoft-specific way of dealing with concatenation?

Havv ei got zee opchions wronk?

[Rolf Magnus]

dejan budimir wrote:

hi there!

#include <iostream>
using namespace std;

void main(){
main() must return int.

int i=0,
j=10;

//Case one (the 'common' case):
cout<< "i == " << i << endl
<< "j == " << j << endl;

//Case two (the 'oddity'):
//Should print 1 and 11 (but will not evaluate the former expression
// before the latter, although it is printing in the correct order.
cout<< "(i+=1) == " <<(i+=1)<< endl
<< "(j+=i) == " <<(j+=i)<< endl;
This invokes undefined behaviour because both i and j are modified twice
without a sequence point in between. In theory, anything can happen.
}

The ostream's operator<<() method is defined as to be passed only two
arguments a time, one of which must be the class, which is being
returned to allow concatenation.

(cout<<expr1)<<expr2;

But it seems as if the whole set of expressions is being evaluated,
_before_ becoming the arguments of the operator methods and, in
addition, is being evaluated from the right to the left (from the
stack?).
Probably, but the C++ standard doesn't state any order of evaluation.
Is this a microsoft-specific way of dealing with concatenation?

Havv ei got zee opchions wronk?

--
"Time flies like an arrow. Fruit flies like a banana."
- Groucho Marx

[dejan budimir]

thanks! that really was fast.
would be great to know what it actually is that "goes wrong", though.
but, since i'll have to learn assembly anyway, i guess it's just a
matter of banana.

have a nice one!

[Karl Heinz Buchegger]

dejan budimir wrote:

thanks! that really was fast.
would be great to know what it actually is that "goes wrong", though.

What "goes wrong": The way you wrote your program.
The C++ language simply does not define what should happen in this case.

--
Karl Heinz Buchegger
kb******@gascad.at

[dejan budimir]

Karl Heinz Buchegger wrote:

dejan budimir wrote:

thanks! that really was fast.
would be great to know what it actually is that "goes wrong", though.

What "goes wrong": The way you wrote your program.
The C++ language simply does not define what should happen in this case.

yes, thank you.