Handling OS function name mismatch with macros

Question

My current code is:

int my_func(int a) 
{
    #ifdef _WIN32
    return _func(a);
    #else
    return func(a);
    #endif
}

But I think it would be better if it was something like:

#ifdef _WIN32
#define common_func(a) _func(a);
#else
#define common_func(a) func(a);
#endif

int my_func(int a) 
{
    return common_func(a);
}

Now, I have never done this and I don't know what I am doing. The K&R cat() example is confusing. I basically just want to get the #ifdefs out of the function because it would get too messy because I have to run the function several times.

func() and _func() are the same function, just Windows thought it would be a great idea to prepend it with an underscore. So it's not even a macro function but more like a function alias maybe. Or a wrapper?

Does this impact performance? Does the generated code differ from version 1? Is there some trick, since the difference is just the underscore?

I want to do it correctly and properly. Please help.

Both coding snippets look equivalent after compilation (in fact, even before, right after preproessing). — , Oct 26 '22 at 13:57
C doesn't have namespace like C++, pretty much everything is in the global namespace. The Win32 API is already huge so it'll be an extremely silly idea to introduce tons of POSIX APIs into the already polluted namespace. [What is the purpose of Microsoft's underscore C functions?](https://stackoverflow.com/q/37845163/995714) — phuclv, Oct 26 '22 at 15:19

John Bollinger · Accepted Answer · 2022-10-26T15:13:43.277

Windows thought it would be a great idea to prepend it with an underscore. So it's not even a macro function but more like a function alias maybe. Or a wrapper?

Most likely it's simply a differently-named function that has the same specifications. Probably not a wrapper or alias. Functions such as POSIX open(), read(), and write() are not defined by the C language specification, unlike corresponding fopen(), fread(), and fwrite(). Generally speaking, C implementations must provide the latter group, by they have no obligation to provide the former group.

Does this impact performance?

Conditional compilation directives such as #ifdef are evaluated at compile time. They themselves have no runtime impact at all, and they are pretty cheap at compile time.

Does the generated code differ from version 1?

No. The two versions of your code are 100% equivalent.

Is there some trick, since the difference is just the underscore?

If there are several functions you want to use where the Windows versions differ in name from (I suppose) the POSIX version by a leading underscore, then you might think it worth your while to define a common macro that you can reuse for all of them, instead of rolling a separate thing for each individual function. Maybe something like this:

#ifdef _WIN32
#define POSIX_MANGLE(f) _ ## f
#else
#define POSIX_MANGLE(f) f
#endif

You would use that something like so:

void do_something(int a) {
    POSIX_MANGLE(func1)(a);
    POSIX_MANGLE(func2)(a);
}

On Windows (technically, wherever _WIN32 is defined), that is then equivalent to ...

void do_something(int a) {
    _func1(a);
    _func2(a);
}

Anywhere else, it is equivalent to ...

void do_something(int a) {
    func1(a);
    func2(a);
}

Since everybody recommends indenting with `if` and `else` statements, why do so few people not indent with `#if` and `#else` statements? The `#define` statements do not have to start in the first column. — Eric Postpischil, Oct 26 '22 at 15:20
is there some naming convention for function macros? I feel like they should be capitalized like every other #define. Is it case-sensitive? Can I, for instance name my define FUNC(a) func(a)? — devgirl05, Oct 26 '22 at 16:33
@devgirl05, it is common, but not obligatory, to use ALL_CAPS macro names. Uppercase Latin letters are definitely permitted, and are distinct from lowercase letters, but there is no universal convention. If you are working with a team, however, or for an organization larger than just yourself, then there may be coding conventions specific to those work arrangements, with which you are expected to comply. — John Bollinger, Oct 26 '22 at 17:00

Handling OS function name mismatch with macros

1 Answers1