How can I wrap iconv_t in boost::scope::unique_resource in just one line? about scope HOT 5 CLOSED

Yes, it looks like you have to define resource traits in this case.

from scope.

In C++20 you could work around it with something like this:

struct invalid_iconv
{
    operator iconv_t() const noexcept
    {
        return (iconv_t)(-1);
    }
};

using unique_iconv_t = boost::scope::unique_resource<iconv_t, boost::core::functor<iconv_close>, boost::scope::unallocated_resource<invalid_iconv{}>>;

but this is a hack and is not much shorter code than the proper resource traits.

from scope.

Thank you for the explanation. What puzzles me is that iconv_t is actually void*, and a Windows HANDLE is also a void*, and INVALID_HANDLE_VALUE is defined as:

#define INVALID_HANDLE_VALUE ((HANDLE)(LONG_PTR)-1)

It looks exactly the same as (iconv_t)(-1). So why is this working?

using unique_handle = boost::scope::unique_resource<
    HANDLE,
    boost::core::functor< CloseHandle >,
    boost::scope::unallocated_resource< INVALID_HANDLE_VALUE, (HANDLE)NULL >
>;

Could it be that MSVC is more permissive than GCC?

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Could it be that MSVC is more permissive than GCC?

Apparently so. You can see in this CI run that MSVC succeeded but clang and gcc on Windows failed to compile this code.

Looks like I should remove the INVALID_HANDLE_VALUE example from the docs, or at least note that this code only works on MSVC.

from scope.

Got it, thank you.

from scope.