What's the point of g++ -Wreorder?

c++, compiler-warnings, g++

Solution

Consider:

struct A {
    int i;
    int j;
    A() : j(0), i(j) { }
};

Now `i` is initialized to some unknown value, not zero.

Alternatively, the initialization of `i` may have some side effects for which the order is important. E.g.

A(int n) : j(n++), i(n++) { }

Problem

The g++ -Wall option includes -Wreorder. What this option does is described below. It is not obvious to me why somebody would care (especially enough to turn this on by default in -Wall). ``` -Wreorder (C++ only) Warn when the order of member initializers given in the code does not match the order in which they must be executed. For instance: struct A { int i; int j; A(): j (0), i (1) { } }; The compiler will rearrange the member initializers for i and j to match the declaration order of the members, emit-ting a warning to that effect. This warning is enabled by -Wall. ```

Original source