In previous versions of the standard (C++03) the order of evaluation of parameters to a function call was unspecified.
Has this been changed in subsequent version of the standard (C++11 or C++14)?
i.e. Can we rely on a specific ordering (left to right) or not.
No this has not changed but there is a very recent proposal to change this: N4228: Refining Expression Evaluation Order for Idiomatic C++, this was part of the Pre-Urbana mailing that came out this October The introduction says (emphasis mine going forward):
Expression evaluation order is a recurring discussion topic in the C++ community. In a nutshell, given an expression such as f(a, b, c), the order in which the sub-expressions f , a , b , c are evaluated is left unspecified by the standard. If any two of these sub-expressions happen to modify the same object without intervening sequence points, the behavior of the program is undefined. For instance, the expression f(i++, i) where i is an integer variable leads to undefined behavior
it proposes:
We propose to revise C++ evaluation rules to support decades-old idiomatic constructs and programming practices. A simple solution would be to require that every expression has a well-defined evaluation order. That suggestion has traditionally met resistance for various reasons. Rather, this proposes suggests a more targeted fix
- Postfix expressions are evaluated from left to right. This includes functions calls and member section expressions.
- Assignment expressions are evaluated from right to left. This includes compound assignments.
- Operands to shift operators are evaluated from left to right
Update
Herb Sutter recently put out a poll on order of evaluation looking for some feedback from the community on what result we would expect from the following code:
std::vector<int> v = { 0, 0 };
int i = 0;
v[i++] = i++;
std::cout << v[0] << v[1] << endl;
This would seem to indicate the committee is looking at the topic of order of evaluation seriously but as we can see from the discussion this is controversial.