# mongoc_cursor_t

## Client-side cursor abtraction

## Synopsis

    typedef struct _mongoc_cursor_t mongoc_cursor_t;

mongoc_cursor_t provides access to a MongoDB query cursor. It wraps up the wire protocol negotiation required to initiate a query and retrieve an unknown number of documents. Cursors are lazy, meaning that no network traffic occurs until the first call to mongoc_cursor_next(). At that point we can:

- Determine which host we've connected to with mongoc_cursor_get_host().

- Retrieve more records with repeated calls to mongoc_cursor_next().

- Test for more records with mongoc_cursor_more()

- Clone a query to repeat execution at a later point with mongoc_cursor_clone().

- Test for errors with mongoc_cursor_error().

## Thread Safety

mongoc_cursor_t is NOT thread safe. It may only be used from the thread it was created from.

## Example

### Query MongoDB and iterate results

    /* gcc example.c -o example $(pkg-config --cflags --libs libmongoc-1.0) */

    /* ./example-client [CONNECTION_STRING [COLLECTION_NAME]] */

    #include <mongoc.h>
    #include <stdio.h>
    #include <stdlib.h>

    int
    main (int   argc,
          char *argv[])
    {
       mongoc_client_t *client;
       mongoc_collection_t *collection;
       mongoc_cursor_t *cursor;
       bson_error_t error;
       const bson_t *doc;
       const char *uristr = "mongodb://127.0.0.1/";
       const char *collection_name = "test";
       bson_t query;
       char *str;

       mongoc_init ();

       if (argc > 1) {
          uristr = argv [1];
       }

       if (argc > 2) {
          collection_name = argv [2];
       }

       client = mongoc_client_new (uristr);

       if (!client) {
          fprintf (stderr, "Failed to parse URI.\n");
          return EXIT_FAILURE;
       }

       bson_init (&query);

    #if 0
       bson_append_utf8 (&query, "hello", -1, "world", -1);
    #endif

       collection = mongoc_client_get_collection (client, "test", collection_name);
       cursor = mongoc_collection_find (collection,
                                        MONGOC_QUERY_NONE,
                                        0,
                                        0,
                                        0,
                                        &query,
                                        NULL,  /* Fields, NULL for all. */
                                        NULL); /* Read Prefs, NULL for default */

       while (mongoc_cursor_next (cursor, &doc)) {
          str = bson_as_json (doc, NULL);
          fprintf (stdout, "%s\n", str);
          bson_free (str);
       }

       if (mongoc_cursor_error (cursor, &error)) {
          fprintf (stderr, "Cursor Failure: %s\n", error.message);
          return EXIT_FAILURE;
       }

       bson_destroy (&query);
       mongoc_cursor_destroy (cursor);
       mongoc_collection_destroy (collection);
       mongoc_client_destroy (client);

       mongoc_cleanup ();

       return EXIT_SUCCESS;
    }