ACliC (gcc) vs CINT

[system]

I wrote a simple macro void a(int i, int j , int k){ printf(" i = %d , j = %d , k=%d\n",i,j,k); } void textpp() { int i =0; a(i++,i++,i++); } and execute it via CINT and via ACliC within one and the same ROOT session:

root.exe [0] .x textpp.cxx i = 0 , j = 1 , k=2 root.exe [1] .x textpp.cxx++ Info in <TUnixSystem>: creating shared . . . i = 2 , j = 1 , k=0 root.exe [2]Could someone explain me why the results are different and which one is correct

[Axel]

Hi Valeri,

both are correct. The standard 8.3.6(9) says it’s unspecified.

Axel.

[tpochep]

void textpp() {
  int i =0;
  a(i++,i++,i++);
}

This programm contains undefined behavior. First, the order in which arguments evaluated is not specified. But it doesn’t matter - your programm violates 5/4 :

Between the previous
and next sequence point a scalar object shall have its stored value modified at most once by the evaluation
of an expression. Furthermore, the prior value shall be accessed only to determine the value to be stored.
The requirements of this paragraph shall be met for each allowable ordering of the subexpressions of a full
expression; otherwise the behavior is undefined.

So, none of your results is correct.

[system]

gcc on Linux and Solaris-10: 2 1 0
icc on Linux and cc on Solaris-10, CINT : 0 1 2

qed: don’t do it