I’ve generated some bindings from the RocksDB C headers, and I’m trying to open a database. This is ...

# kotlin-native

[Adam S]

I’ve generated some bindings from the RocksDB C headers, and I’m trying to open a database. This is the generated binding:

public external expect fun rocksdb_open(
  options: CValuesRef<rocksdb_options_t>?, 
  name: String?, 
  errptr: CValuesRef<CPointerVar<ByteVar>>?
): CPointer<rocksdb_t>?

I need to pass in errptr, but how can I create a value with type CValuesRef<CPointerVar<ByteVar>>?

[kevin.cianfarini]

str.cstr.ptr.

You need to free the memory this allocates afterwards.

[kevin.cianfarini]

What is the C type it's looking for?

[Adam S]

extern ROCKSDB_LIBRARY_API rocksdb_t* rocksdb_open(
    const rocksdb_options_t* options, const char* name, char** errptr);

[kevin.cianfarini]

It's looking for an array of strings, not a single string.

[kevin.cianfarini]

look at allocArrayOfPointersTo

[kevin.cianfarini]

for your strings.

[Adam S]

ahh okay, that’s weird. There’s no comments/docs on the C API so I’m a bit lost

[Adam S]

thanks, I’ll take a look

[kevin.cianfarini]

It's hard to tell you exactly what you need without more context, but I think that will be helpful

[kevin.cianfarini]

You could also consider using allocArray

[Adam S]

unfortunately this is all the context I have

// open DB
  char *err = NULL;
  db = rocksdb_open(options, DBPath, &err);
  assert(!err);

[vbsteven]

Could be something like

val err = allocPointerTo<ByteVar>()

[Adam S]

nice, thanks! allocPointerTo<ByteVar>() compiles

memScoped {
    val err = allocPointerTo<ByteVar>()
    val db = rocksdb_open(
      options,
      "rdb_test_01",
      err.ptr,
    )

    var result = err.pointed?.value
    require(result == null) {
      "error opening db: $result"
    }