Connecting to Redis on hiredis (C++)

Prerequisites

• A Redis instance is created, and is in the Running state.
• An ECS has been created. For details about how to create an ECS, see Elastic Cloud Server User Guide
• If the ECS runs the Linux OS, ensure that the GCC compilation environment has been installed on the ECS.

Connecting to Redis on hiredis

1. View the IP address/domain name and port number of the DCS Redis instance to be accessed.

   For details, see Distributed Cache Service User Guide > "Getting Started" > "Viewing Details of a DCS Instance".

2. Log in to the ECS.

   The following uses CentOS as an example to describe how to access an instance in C++.

3. Install GCC, Make, and hiredis.

   If the system does not provide a compiling environment, run the following yum command to install the environment:

   yum install gcc make

4. Run the following command to download and decompress the hiredis package:

   wget https://github.com/redis/hiredis/archive/master.zip
   unzip master.zip

5. Go to the directory where the decompressed hiredis package is saved, and compile and install hiredis.

   make
   make install

6. Access the DCS instance by using hiredis.

   The following describes connection and password authentication of hiredis. For more information on how to use hiredis, visit the Redis official website.

   1. Edit the sample code for connecting to a DCS instance, and then save the code and exit.

      vim connRedis.c

      Example:

      #include <stdio.h>
      #include <stdlib.h>
      #include <string.h>
      #include <hiredis.h>
      int main(int argc, char **argv) {
           unsigned int j;
           redisContext *conn;
           redisReply *reply;
           if (argc < 3) {
                   printf("Usage: example {instance_ip_address} 6379 {password}\n");
                   exit(0);
           }
           const char *hostname = argv[1];
           const int port = atoi(argv[2]);
           const char *password = argv[3];
           struct timeval timeout = { 1, 500000 }; // 1.5 seconds
           conn = redisConnectWithTimeout(hostname, port, timeout);
           if (conn == NULL || conn->err) {
      		if (conn) {
                   printf("Connection error: %s\n", conn->errstr);
                   redisFree(conn);
      		} else {
                   printf("Connection error: can't allocate redis context\n");
      		}
           exit(1);
           }
           /* AUTH */
           reply = redisCommand(conn, "AUTH %s", password);
           printf("AUTH: %s\n", reply->str);
           freeReplyObject(reply);
      
           /* Set */
           reply = redisCommand(conn,"SET %s %s", "welcome", "Hello, DCS for Redis!");
           printf("SET: %s\n", reply->str);
           freeReplyObject(reply);
      
           /* Get */
           reply = redisCommand(conn,"GET welcome");
           printf("GET welcome: %s\n", reply->str);
           freeReplyObject(reply);
      
           /* Disconnects and frees the context */
           redisFree(conn);
           return 0;
      }

   2. Run the following command to compile the code:

      gcc connRedis.c -o connRedis  -I /usr/local/include/hiredis -lhiredis

      If an error is reported, locate the directory where the hiredis.h file is saved and modify the compilation command.

      After the compilation, an executable connRedis file is obtained.

   3. Run the following command to access the chosen DCS Redis instance:

      ./connRedis {redis_instance_address} 6379 {password}

      {redis_instance_address} indicates the IP address/domain name of DCS instance and 6379 is an example port number of DCS instance. For details about how to obtain the IP address/domain name and port, see 1. Change them as required. {password} indicates the password used to log in to the chosen DCS Redis instance. This password is defined during DCS Redis instance creation.

      You have successfully accessed the instance if the following command output is displayed:

      AUTH: OK
      SET: OK
      GET welcome: Hello, DCS for Redis!

   

   If an error is reported, indicating that the hiredis library files cannot be found, run the following commands to copy related files to the system directories and add dynamic links:

   mkdir /usr/lib/hiredis
   cp /usr/local/lib/libhiredis.so.0.13 /usr/lib/hiredis/
   mkdir /usr/include/hiredis
   cp /usr/local/include/hiredis/hiredis.h /usr/include/hiredis/
   echo '/usr/local/lib' >>;>>;/etc/ld.so.conf
   ldconfig

   Replace the locations of the so and .h files with actual ones before running the commands.