Welcome to another lesson of this course, leveraging C++ for interacting with RESTful APIs. In our previous lessons, we established a foundation by learning about RESTful APIs and executing GET requests using C++ libraries. Now, we will shift our focus to path and query parameters, essential tools for refining API requests and fetching specific data.

Path and query parameters are vital for making your API requests more precise and efficient. Imagine you are shopping online: selecting a specific item using its ID is similar to a path parameter, while filtering items by categories like price or color resembles query parameters. In this lesson, we'll explore these concepts with practical examples, empowering you to extract just the information you need from an API using C++.

Path parameters are part of the URL used to access specific resources within an API, acting like unique identifiers. For example, if you want to retrieve a to-do item with ID 3, the URL would be structured as follows:

In this case, 3 is the path parameter specifying the particular item you wish to access.

Query parameters are added to the URL after a ? to filter or modify the data returned by the API. They are formatted as key-value pairs. For instance, if you want to list only the completed to-do tasks, your request would be:

Here, done=true is the query parameter filtering the results to include only tasks that are marked as completed.

Before jumping into implementing these parameters using C++, let's ensure everything is set up correctly. We will use the httplib library to handle HTTP requests and the nlohmann::json library to manage JSON responses. Here’s how to set up the HTTP client:

Path parameters are utilized to target specific resources within an API, allowing direct access to individual items. They are appended directly to the endpoint URL. For instance, if you want to fetch the details of a specific to-do item using its ID, you can use a path parameter.

Here's a practical example using ID 3:

In this example, the todo_id is a path parameter specifying the to-do item with ID 3, and the full URL looks like http://localhost:8000/todos/3. If successful, you'll get an output displaying the task details:

Query parameters are added to the URL to filter or modify the data returned by the API. They are especially useful for searching or narrowing down data without altering the overall resource structure.

Let's filter the to-do items to list only those marked as done:

Here, the query parameter done=true is used to filter the results. The full URL in this case looks like http://localhost:8000/todos?done=true, focusing only on completed tasks. If successful, the output will list the tasks that are marked as done, emphasizing how query parameters can streamline outputs by highlighting specific criteria:

To further refine data retrieval, you can combine multiple query parameters. For example, you might want to fetch to-do items that are marked as done and also have titles starting with a specific prefix.

Here's how you can filter to-do items that are completed and have titles starting with the prefix "c":

In this example, the query parameters done=true and title=c are used together to filter the results. The URL in this request will look like http://localhost:8000/todos?done=true&task=c, retrieving items that are both completed and begin with "c". If successful, the output will be:

In this lesson, you’ve gained insight into using both path and query parameters to refine API requests. Path parameters allow you to target specific resources, whereas query parameters tailor the results based on defined conditions. Together, they provide a robust mechanism for fetching targeted information from an API.

You are now prepared to tackle practical exercises, where these concepts will be applied to further reinforce your understanding. These skills are essential for effective API interactions, laying the groundwork for more advanced operations as you progress through the course. Continue to apply what you've learned and explore new variations as you move forward!