---
name: "mongoc_client_t"
section: "3"
platform: "linux"
package: "libmongoc-doc"
version: "1.30.4-1+deb13u3"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/mongoc_client_t"
---

# mongoc\_client\_t(3)

A single-threaded MongoDB connection. See *Connection Pooling*.

## SYNOPSIS

```
typedef struct _mongoc_client_t mongoc_client_t;
typedef mongoc_stream_t *(*mongoc_stream_initiator_t) (
   const mongoc_uri_t *uri,
   const mongoc_host_list_t *host,
   void *user_data,
   bson_error_t *error);
```

**mongoc\_client\_t** is an opaque type that provides access to a MongoDB server, replica set, or sharded cluster. It maintains management of underlying sockets and routing to individual nodes based on *mongoc\_read\_prefs\_t* or *mongoc\_write\_concern\_t*.

## STREAMS

The underlying transport for a given client can be customized, wrapped or replaced by any implementation that fulfills *mongoc\_stream\_t*. A custom transport can be set with *mongoc\_client\_set\_stream\_initiator()*.

## THREAD SAFETY

**mongoc\_client\_t** is *NOT* thread-safe and should only be used from one thread at a time. When used in multi-threaded scenarios, it is recommended that you use the thread-safe *mongoc\_client\_pool\_t* to retrieve a **mongoc\_client\_t** for your thread.

## FORK SAFETY

A *mongoc\_client\_t* is only usable in the parent process after a fork. The child process must call *mongoc\_client\_reset()*.

## EXAMPLE

example-client.c

```
/* gcc example-client.c -o example-client $(pkg-config --cflags --libs
 * libmongoc-1.0) */
/* ./example-client [CONNECTION_STRING [COLLECTION_NAME]] */
#include <mongoc/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 *collection_name = "test";
   bson_t query;
   char *str;
   const char *uri_string = "mongodb://127.0.0.1/?appname=client-example";
   mongoc_uri_t *uri;
   mongoc_init ();
   if (argc > 1) {
      uri_string = argv[1];
   }
   if (argc > 2) {
      collection_name = argv[2];
   }
   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }
   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }
   mongoc_client_set_error_api (client, 2);
   bson_init (&query);
   collection = mongoc_client_get_collection (client, "test", collection_name);
   cursor = mongoc_collection_find_with_opts (collection,
                                              &query,
                                              NULL,  /* additional options */
                                              NULL); /* read prefs, NULL for default */
   while (mongoc_cursor_next (cursor, &doc)) {
      str = bson_as_canonical_extended_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_uri_destroy (uri);
   mongoc_client_destroy (client);
   mongoc_cleanup ();
   return EXIT_SUCCESS;
}
```

## AUTHOR

MongoDB, Inc

## COPYRIGHT

2009-present, MongoDB, Inc.