Welcome back! Now that you've learned how to work with numbers in Redis, it's time to build on that knowledge and explore some basic operations with these numbers. This lesson will show you how to perform operations like incrementing, decrementing, and modifying numeric values directly in Redis.
In this lesson, you will learn how to:
- Increment and decrement numeric values.
- Modify numeric values using operations such as increments by a floating point.
Here's the code snippet that we'll be working with:
C++1#include <iostream> 2#include <hiredis/hiredis.h> 3 4int main() { 5 // Connect to Redis 6 redisContext* context = redisConnect("127.0.0.1", 6379); 7 if (context == nullptr || context->err) { 8 if (context) { 9 std::cerr << "Error: " << context->errstr << std::endl; 10 redisFree(context); 11 } else { 12 std::cerr << "Can't allocate redis context" << std::endl; 13 } 14 return 1; 15 } 16 17 // Setting initial values 18 redisCommand(context, "SET count %d", 5); 19 redisCommand(context, "SET completion_rate %f", 95.5); 20 redisCommand(context, "SET duration %d", 0); 21 22 // Perform operations 23 redisCommand(context, "DECR count"); 24 redisCommand(context, "INCRBYFLOAT completion_rate 1.5"); 25 redisCommand(context, "INCR duration"); 26 27 // Retrieve and print values 28 redisReply* reply; 29 30 reply = (redisReply*)redisCommand(context, "GET count"); 31 std::cout << "Course count: " << reply->str << std::endl; 32 freeReplyObject(reply); 33 34 reply = (redisReply*)redisCommand(context, "GET completion_rate"); 35 std::cout << "Completion rate: " << reply->str << std::endl; 36 freeReplyObject(reply); 37 38 reply = (redisReply*)redisCommand(context, "GET duration"); 39 std::cout << "Duration: " << reply->str << std::endl; 40 freeReplyObject(reply); 41 42 // Cleanup 43 redisFree(context); 44 return 0; 45} 46// Expected Output: 47// Course count: 4 48// Completion rate: 97 49// Duration: 1
Let's break it down:
-
After setting initial values for
count
,completion_rate
, andduration
, we perform various operations:- The command
DECR count
decreases the value ofcount
by 1. You can also provide a second argument to decrement by a specific value:DECRBY count 2
will decrementcount
by 2.DECR
commands are used only for integer values. - The command
INCRBYFLOAT completion_rate 1.5
incrementscompletion_rate
by 1.5. This method is versatile for both integer and floating-point values. - The command
INCR duration
increasesduration
by 1. This can be modified by a specific increment value:INCRBY duration 5
will increaseduration
by 5.INCR
commands should also be used on integer values.
- The command
-
Finally, we retrieve the updated values using
GET
commands and print them to show the current stage.
Understanding how to perform operations with numbers in Redis is essential for real-world applications. Imagine you're building a learning management system: you would track user progress, completion rates, and time spent on courses. Redis makes it fast and easy to update these numbers in real-time.
By the end of this lesson, you'll be comfortable with basic numeric operations in Redis, preparing you for more advanced tasks. Ready to get started? Let's dive into the practice section and enhance your Redis skills!