Been looking through some of the mappings generate...

# kotlin-native

[napperley]

Been looking through some of the mappings generated for the libudev library:

public fun udev_list_entry_get_by_name(list_entry: kotlinx.cinterop.CValuesRef<cnames.structs.udev_list_entry>?, @kotlinx.cinterop.internal.CCall.CString name: kotlin.String?): kotlinx.cinterop.CPointer<cnames.structs.udev_list_entry>? { /* compiled code */ }

public fun udev_list_entry_get_name(list_entry: kotlinx.cinterop.CValuesRef<cnames.structs.udev_list_entry>?): kotlinx.cinterop.CPointer<kotlinx.cinterop.ByteVar /* = kotlinx.cinterop.ByteVarOf<kotlin.Byte> */>? { /* compiled code */ }

public fun udev_list_entry_get_next(list_entry: kotlinx.cinterop.CValuesRef<cnames.structs.udev_list_entry>?): kotlinx.cinterop.CPointer<cnames.structs.udev_list_entry>? { /* compiled code */ }

public fun udev_list_entry_get_value(list_entry: kotlinx.cinterop.CValuesRef<cnames.structs.udev_list_entry>?): kotlinx.cinterop.CPointer<kotlinx.cinterop.ByteVar /* = kotlinx.cinterop.ByteVarOf<kotlin.Byte> */>? { /* compiled code */ }

There doesn't appear to be a definition in any of the knm files for udev_list_entry (a C struct), however cnames.structs.udev_list_entry does exist but its definition doesn't seem to appear in any of the knm files which is strange.

[msink]

In libudev.h it just declared as opaque handle struct udev_list_entry;, and defined in libudev-internal.h
So if you want to access it's fields - add libudev-internal.h to headers in .def file

[napperley]

Does the cnames.structs.x indicate that there is a Struct used in the C lib which the cinterop tool cannot find the definition for?

[napperley]

The libudev-internal.h file doesn't exist in the libudev-dev deb package.

[msink]

Of course, it is internal, but available in libudev (now part of systemd) sources on github.

[msink]

Well, sorry, I messed something - it isn't available in header, just in C source
And seems that implementation is different in different versions.

[napperley]

Presumably Kotlin Native only supports C interop via header files. Would be good if the cinterop tool supported C source files, which would likely resolve the current problem.

[napperley]

Looks as though I will have to look at an alternative C library (eg libusb - https://libusb.info/ ).

[olonho]

it’s forward declaration, and can be used as such. It corresponds to struct Foo in C header, and is common way if declaring opaque handle type. It could be used from K/N same way as from C.

[olonho]

interop can use declarations from .h or .c files, it doesn’t care, and you can add it to headers, or copy-paste structure declaration to .def file after ---.