How can I concisely assign to the members of a struct depending on a condition?

Question

I have some code that looks like this:

struct mystruct
{
    /* lots of members */
};

void mystruct_init( struct mystruct* dst, int const condition )
{
    if ( condition )
    {
        /* initialize members individually a certain way */
    }
    else
    {
        /* initialize members individually another way */
    }
}

Options I'm considering:

• Simplest would be to have a function that assigns to every member and call that. Should I simply hope the compiler optimizes that call away?
• Define a macro to explicitly avoid the function call overhead.
• Write everything the long way.

What is the proper way to handle such a scenario in C11?

Answer 1

Just write a function that initializes a member, or if you want (opinion based), use a MACRO.

By the way, I would personally do it like this:

void mystruct_init( struct mystruct* dst, int const condition )
{
    if ( condition )
        init_first_way(..);
    else
        init_second_way(..);
}

or just use the ternary operator. Remember, you care about readability and always have in mind:

Simplicity is a virtue!

---

I really think worrying about optimization at this stage will make a victim of immature optimization, since I doubt it will be the bottleneck.

In general, if you want to optimize your code, profile your code(while it runs with optimization flags, many people do not know this, I was one of them: Poor performance of stl list on vs2015 while deleting nodes which contain iterator to self's position in list), find the bottleneck and try to optimize that bottleneck.

Answer 2

I do not think that there is any clear rule here. To me, it depends on the taste of the author.

Two obvious ways are:

// initialize members that are independent of 'condition'

if (condition) {
  // initialize members one way
}
else {
  // initialize members another way
}

The same may be written as:

// initialize members that are independent of 'condition'

// initialize members based on 'condition'
dst->memberx = condition ? something : something_else;
// ...

Please do not worry about one function call overhead.