mongoc_collection_estimated_document_count (mongoc_collection_t *collection,
                                            const bson_t *opts,
                                            const mongoc_read_prefs_t *read_prefs,
                                            bson_t *reply,
                                            bson_error_t *error);


opts may be NULL or a BSON document with additional command options:

  • skip: An int specifying how many documents matching the query should be skipped before counting.

  • limit: An int specifying the maximum number of documents to count.

  • comment: A bson_value_t specifying the comment to attach to this command. The comment will appear in log messages, profiler output, and currentOp output. Requires MongoDB 4.4 or later.

For a list of all options, see the MongoDB Manual entry on the count command.


This functions executes a count query on collection. In contrast with mongoc_collection_count_documents(), the count returned is not guaranteed to be accurate.

This function is considered a retryable read operation. Upon a transient error (a network error, errors due to replica set failover, etc.) the operation is safely retried once. If retryreads is false in the URI (see mongoc_uri_t) the retry behavior does not apply.


This method is implemented using the count command. Due to an oversight in versions 5.0.0-5.0.8 of MongoDB, the count command was not included in version “1” of the Stable API. Applications using this method with the Stable API are recommended to upgrade their server version to 5.0.9+ or disable strict mode (via :symbol:`mongoc_server_api_strict()) to avoid encountering errors.


Errors are propagated via the error parameter.


-1 on failure, otherwise the number of documents counted.


#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

static void
print_count (mongoc_collection_t *collection, bson_t *query)
   bson_error_t error;
   int64_t count;
   bson_t* opts = BCON_NEW ("skip", BCON_INT64(5));

   count = mongoc_collection_estimated_document_count (
      collection, opts, NULL, NULL, &error);
   bson_destroy (opts);

   if (count < 0) {
      fprintf (stderr, "Count failed: %s\n", error.message);
   } else {
      printf ("%" PRId64 " documents counted.\n", count);

See also