Redis basics using hiredis C

Published on February 19, 2021

Introduction, Downloading & Installing hiredis

Redis is an open source (BSD licensed), in-memory data structure store, used as a database, cache, and message broker.
Redis works with an in-memory dataset. Depending on your use case, you can persist your data either by periodically dumping the dataset to disk or by appending each command to a disk-based log.
To install hiredis goto Link and download tar.gz and run these commands followed by code compiling

tar -xf hiredis-0.14.1.tar.gz
cd hiredis-0.14.1
make install

# To compile code with hiredis
gcc example.c -lhiredis -o example.o

#To run
./example.o

Below is an example code just to check and see hiredis works fine ...

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <hiredis/hiredis.h>

int main (int argc, char **argv) {
    struct redisReply *reply;
    struct redisContext *c;

    /* Redis Constructor */
    c = redisConnect("127.0.0.1", 6379);    // 127.0.0.1:6379
    if (c->err) {
        printf("Failed redisConnect error: %s\n", c->errstr);
        return 1;
    }

    /* PING to check server */
    reply = redisCommand(c,"PING %s", "Hello World");
    printf("RESPONSE: %s\n", reply->str);
    freeReplyObject(reply);

    redisFree(c);
    return 0;
}

Data Structures

Redis provides data structures such as strings, hashes, lists, sets, sorted sets with range queries, bitmaps, hyperloglogs, geospatial indexes, and streams.

Strings

key-value stores. Used to store three types of values: Byte string values, Integer values and Floating-point values.

GET Fetches the data stored at the given key
SET Sets the value stored at the given key
DEL Deletes the value stored at the given key (works for all types)

/* Strings */

// SET
reply = redisCommand(c,"SET x %s", "NICE");
printf("SET X: %s\n", reply->str);
freeReplyObject(reply);

// GET
reply = redisCommand(c,"GET x");
printf("GET X: %s\n", reply->str);
freeReplyObject(reply);

// DEL
reply = redisCommand(c,"DEL x");
printf("DEL X: %lld\n", reply->integer);
freeReplyObject(reply);

INCR, DECR, APPEND, SETRANGE, GETRANGE, BITOP

Lists

linked-list structure. LISTs in Redis store an ordered sequence of strings. We can push items to the front and the back of the LIST with LPUSH/RPUSH, likewise in other commands as well.

RPUSH Pushes the value onto the right end of the list
LRANGE Fetches a range of values from the list
LINDEX Fetches an item at a given position in the list
LPOP Pops the value from the left end of the list and returns it

/* LISTS */

// DEL
reply = redisCommand(c,"DEL myList");
printf("DEL myList: %lld\n", reply->integer);
freeReplyObject(reply);

// RPUSH
reply = redisCommand(c,"RPUSH myList abc.def");
redisCommand(c,"RPUSH myList hij.klm");
redisCommand(c,"RPUSH myList nop.qrs");
redisCommand(c,"RPUSH myList REMOVEEEE");
printf("RPUSH myList: %lld\n", reply->integer);
freeReplyObject(reply);

// LPOP
reply = redisCommand(c,"LPOP myList");
printf("LPOP X: %lld\n", reply->integer);
freeReplyObject(reply);

// LIST iterate and print
reply = redisCommand(c,"LRANGE myList 0 -1");

if (reply->type == REDIS_REPLY_ARRAY) {
    for (int j = 0; j < reply->elements; j++) {
        printf("%s, ",reply->element[j]->str);
    }
    printf("\n");
}
freeReplyObject(reply);

Hashes

coming soon...

Sets

coming soon...

Sorted Sets

coming soon...

If you like it, share it!

abiDEV diary

Abid Zaidi

Abid Zaidi

Tech Topics