Evaluation Order of Subscript Operator

Question

Does there exist any order for evaluation of expressions in case of an array. If an expression E is of the form E1[E2], where E1 & E2 are also expressions, is the order of evaluation of E1 & E2 fixed ?

Here is my code :

#include<stdio.h>
int main(){

    int a[5] = {1,2,3,4,5}; 
    (a + printf("1"))[printf("2")];
    (printf("3"))[a + printf("4")];

    return 0;
}   

It's showing output as: 1243

I'v compiled it with gcc.

Thanks.

Answer 1

E1[E2] is equivalent of *(E1 + E2).

And the Standard tells that "the order of evaluation of subexpressions and the order in which side effects take place are both unspecified". So, the order of evaluation of E1[E2] is not fixed.

Answer 2

N1256:

6.5 Expressions
...
3 The grouping of operators and operands is indicated by the syntax.⁷⁴⁾ Except as specified later (for the function-call (), &&, ||, ?:, and comma operators), the order of evaluation of subexpressions and the order in which side effects take place are both unspecified.

So the short answer is "no"; for an expression like E1[E2], the order in which the subexpressions E1 and E2 are evaluated is not fixed.