Don't depend on order of evaluation of function arguments

Reason

Because that order is unspecified.

Note

C++17 tightens up the rules for the order of evaluation, but the order of evaluation of function arguments is still unspecified.

Example

int i = 0;
f(++i, ++i);

Before C++17, the behavior is undefined, so the behavior could be anything (e.g., f(2, 2)). Since C++17, this code does not have undefined behavior, but it is still not specified which argument is evaluated first. The call will be f(1, 2) or f(2, 1), but you don't know which.

Example

Overloaded operators can lead to order of evaluation problems:

f1()->m(f2());          // m(f1(), f2())
cout << f1() << f2();   // operator<<(operator<<(cout, f1()), f2())

In C++17, these examples work as expected (left to right) and assignments are evaluated right to left (just as ='s binding is right-to-left)

f1() = f2();    // undefined behavior in C++14; in C++17, f2() is evaluated before f1()

Enforcement

Can be detected by a good analyzer.