[Bug c/44918] New: Calculation on y = x++ + x++ depends on following statements

[Bug c/44918] New: Calculation on y = x++ + x++ depends on following statements

[eric dot liu at uniquesoft dot com]

#include <stdio.h>

void UnspecifiedSideEffectInExpression(int c)
{
        int x = 0, y = 0, z = 20, t = 30, *p, *q;

        x = c;
        y = x++ + x++;
        printf("x = %d, y = %d\n", x, y);

        //Comment out the following code to get a different result
        p = (c&2) ? &x : &t;
        printf("*p = %d\n", *p);

}

int main()
{
        UnspecifiedSideEffectInExpression(1);

        return 0;
}


-- 
           Summary: Calculation on y = x++ + x++ depends on following
                    statements
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: eric dot liu at uniquesoft dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44918

[Bug c/44918] Calculation on y = x++ + x++ depends on following statements

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2010-07-12 09:19 -------
There is no sequence point between the two modifications to x.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
   GCC host triplet|CentOS 5.3 on i386          |
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44918

[Bug c/44918] Calculation on y = x++ + x++ depends on following statements

[eric dot liu at uniquesoft dot com]

------- Comment #2 from eric dot liu at uniquesoft dot com  2010-07-12 09:34 -------
I don't understand what is sequence point.
But as a user, I DO want gcc to produce the same result.
As for the code in the bug description, the result is:
x = 2, y = 2
*p = 30

If comment out the code indicated in the bug description, the result is
x = 3, y = 2

The result is different. Why?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44918

[Bug c/44918] Calculation on y = x++ + x++ depends on following statements

[eric dot liu at uniquesoft dot com]

------- Comment #3 from eric dot liu at uniquesoft dot com  2010-07-12 09:49 -------
Refer to my previous comment, I need to reopen it for a correct answer.


-- 

eric dot liu at uniquesoft dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44918

[Bug c/44918] Calculation on y = x++ + x++ depends on following statements

[steven at gcc dot gnu dot org]

------- Comment #4 from steven at gcc dot gnu dot org  2010-07-12 09:54 -------
The correct answer is: "here is no sequence point between the two modifications
to x.".

If you don't know what a sequence point is, use Google (see first hit,
Wikipedia).
If you don't know C, don't use C.
And don't reopen bugs because you're too bloody lazy to do any searching
yourself.


-- 

steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44918