hiredis guide (C) on Docs

Connect

Mon, 01 Jan 0001 00:00:00 +0000

Basic synchronous connection

The example below creates a simple synchronous connection to a local Redis server and tests the connection, before closing it with redisFree(). The redisConnect() function takes just a hostname and port as its arguments, and returns a context object.

Issue commands

Mon, 01 Jan 0001 00:00:00 +0000

Unlike the other client libraries, hiredis doesn't provide an extensive API to construct the many different Redis commands. However, it does provide a lightweight and flexible API to help you construct commands and parse their replies from your own code.

The sections below describe the available functions in detail.

Construct synchronous commands

Use the redisCommand() function to send commands to the server:

Handle command replies

Mon, 01 Jan 0001 00:00:00 +0000

The redisCommand() and redisCommandArgv() functions return a pointer to a redisReply object when you issue a command (see Issue commands for more information). This type supports all reply formats defined in the RESP2 and RESP3 protocols, so its content varies greatly between calls.

A simple example is the status response returned by the SET command. The code below shows how to get this from the redisReply object:

redisReply *reply = redisCommand(c, "SET greeting Hello");

// Check and free the reply.
if (reply != NULL) {
    printf("Reply: %s\n", reply->str);
    freeReplyObject(reply);
    reply = NULL;
}

A null reply indicates an error, so you should always check for this. If an error does occur, then the redisContext object will have a non-zero error number in its integer err field and a textual description of the error in its errstr field.

Pipelines and transactions

Mon, 01 Jan 0001 00:00:00 +0000

Redis lets you send a sequence of commands to the server together in a batch. There are two types of batch that you can use:

Pipelines avoid network and processing overhead by sending several commands to the server together in a single communication. The server then sends back a single communication with all the responses. See the Pipelining page for more information.
Transactions guarantee that all the included commands will execute to completion without being interrupted by commands from other clients. See the Transactions page for more information.

Execute a pipeline

There is no command to explicitly start a pipeline with hiredis, but if you issue a command with the redisAppendCommand() function, it will be added to an output buffer without being sent immediately to the server.