#include <mongoc/mongoc.h>
typedef struct {
   bool is_initialized;
   bool background;
   bool unique;
   const char *name;
   bool drop_dups;
   bool sparse;
   int32_t expire_after_seconds;
   int32_t v;
   const bson_t *weights;
   const char *default_language;
   const char *language_override;
   mongoc_index_opt_geo_t *geo_options;
   mongoc_index_opt_storage_t *storage_options;
   const bson_t *partial_filter_expression;
   const bson_t *collation;
   void *padding[4];
} mongoc_index_opt_t;

dropDups is deprecated as of MongoDB version 3.0.0. This option is silently ignored by the server and unique index builds using this option will fail if a duplicate value is detected.

{
   bson_t keys;
   bson_error_t error;
   mongoc_index_opt_t opt;
   mongoc_index_opt_geo_t geo_opt;
   mongoc_index_opt_init (&opt);
   mongoc_index_opt_geo_init (&geo_opt);
   bson_init (&keys);
   BSON_APPEND_UTF8 (&keys, "location", "2d");
   geo_opt.twod_location_min = -123;
   geo_opt.twod_location_max = +123;
   geo_opt.twod_bits_precision = 30;
   opt.geo_options = &geo_opt;
   collection = mongoc_client_get_collection (client, "test", "geo_test");
   if (mongoc_collection_create_index (collection, &keys, &opt, &error)) {
      /* Successfully created the geo index */
   }
   bson_destroy (&keys);
   mongoc_collection_destroy (&collection);
}

mongoc_index_opt_geo_t

mongoc_index_opt_wt_t