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        printf("Error: %s\n", c->errstr);
        // handle error
    } else {
        printf("Can't allocate redis context\n");
    }
}
```

One can also use `redisConnectWithOptions` which takes a `redisOptions` argument
that can be configured with endpoint information as well as many different flags
to change how the `redisContext` will be configured.

```c
redisOptions opt = {0};

/* One can set the endpoint with one of our helper macros */
if (tcp) {
    REDIS_OPTIONS_SET_TCP(&opt, "localhost", 6379);
} else {
    REDIS_OPTIONS_SET_UNIX(&opt, "/tmp/redis.sock");
}

/* And privdata can be specified with another helper */
REDIS_OPTIONS_SET_PRIVDATA(&opt, myPrivData, myPrivDataDtor);

/* Finally various options may be set via the `options` member, as described below */
opt->options |= REDIS_OPT_PREFER_IPV4;
```

If a connection is lost, `int redisReconnect(redisContext *c)` can be used to restore the connection using the same endpoint and options as the given context.

### Configurable redisOptions flags

There are several flags you may set in the `redisOptions` struct to change default behavior.  You can specify the flags via the `redisOptions->options` member.

| Flag | Description  |
| --- | --- |
| REDIS\_OPT\_NONBLOCK | Tells hiredis to make a non-blocking connection. |
| REDIS\_OPT\_REUSEADDR | Tells hiredis to set the [SO_REUSEADDR](https://man7.org/linux/man-pages/man7/socket.7.html) socket option |
| REDIS\_OPT\_PREFER\_IPV4<br>REDIS\_OPT\_PREFER_IPV6<br>REDIS\_OPT\_PREFER\_IP\_UNSPEC | Informs hiredis to either prefer IPv4 or IPv6 when invoking [getaddrinfo](https://man7.org/linux/man-pages/man3/gai_strerror.3.html).  `REDIS_OPT_PREFER_IP_UNSP...
| REDIS\_OPT\_NO\_PUSH\_AUTOFREE | Tells hiredis to not install the default RESP3 PUSH handler (which just intercepts and frees the replies).  This is useful in situations where you want to process these messages in-band. |
| REDIS\_OPT\_NOAUTOFREEREPLIES | **ASYNC**: tells hiredis not to automatically invoke `freeReplyObject` after executing the reply callback. |
| REDIS\_OPT\_NOAUTOFREE | **ASYNC**: Tells hiredis not to automatically free the `redisAsyncContext` on connection/communication failure, but only if the user makes an explicit call to `redisAsyncDisconnect` or `redisAsyncFree` |

*Note: A `redisContext` is not thread-safe.*

### Other configuration using socket options

The following socket options are applied directly to the underlying socket.
The values are not stored in the `redisContext`, so they are not automatically applied when reconnecting using `redisReconnect()`.
These functions return `REDIS_OK` on success.
On failure, `REDIS_ERR` is returned and the underlying connection is closed.

To configure these for an asynchronous context (see *Asynchronous API* below), use `ac->c` to get the redisContext out of an asyncRedisContext.

```C
int redisEnableKeepAlive(redisContext *c);
int redisEnableKeepAliveWithInterval(redisContext *c, int interval);
```

Enables TCP keepalive by setting the following socket options (with some variations depending on OS):

* `SO_KEEPALIVE`;
* `TCP_KEEPALIVE` or `TCP_KEEPIDLE`, value configurable using the `interval` parameter, default 15 seconds;
* `TCP_KEEPINTVL` set to 1/3 of `interval`;
* `TCP_KEEPCNT` set to 3.

```C
int redisSetTcpUserTimeout(redisContext *c, unsigned int timeout);
```

Set the `TCP_USER_TIMEOUT` Linux-specific socket option which is as described in the `tcp` man page:

> When the value is greater than 0, it specifies the maximum amount of time in milliseconds that trans mitted data may remain unacknowledged before TCP will forcibly close the corresponding connection and return ETIMEDOUT to the application.
> If the option value is specified as 0, TCP will use the system default.

### Sending commands

There are several ways to issue commands to Redis. The first that will be introduced is
`redisCommand`. This function takes a format similar to printf. In the simplest form,
it is used like this:
```c
reply = redisCommand(context, "SET foo bar");
```

The specifier `%s` interpolates a string in the command, and uses `strlen` to
determine the length of the string:
```c
reply = redisCommand(context, "SET foo %s", value);
```
When you need to pass binary safe strings in a command, the `%b` specifier can be
used. Together with a pointer to the string, it requires a `size_t` length argument
of the string:
```c
reply = redisCommand(context, "SET foo %b", value, (size_t) valuelen);
```
Internally, Hiredis splits the command in different arguments and will
convert it to the protocol used to communicate with Redis.
One or more spaces separates arguments, so you can use the specifiers
anywhere in an argument:
```c
reply = redisCommand(context, "SET key:%s %s", myid, value);
```

### Using replies

The return value of `redisCommand` holds a reply when the command was
successfully executed. When an error occurs, the return value is `NULL` and
the `err` field in the context will be set (see section on **Errors**).
Once an error is returned the context cannot be reused and you should set up
a new connection.

The standard replies that `redisCommand` are of the type `redisReply`. The
`type` field in the `redisReply` should be used to test what kind of reply
was received:

### RESP2

* **`REDIS_REPLY_STATUS`**:
    * The command replied with a status reply. The status string can be accessed using `reply->str`.
      The length of this string can be accessed using `reply->len`.