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Customizing C# and C++ with Amazon Q Developer

April 1, 2025 By Mark Otto Off

Amazon Q Developer recently added support for customizing C# and C++ suggestions based on your company’s codebase. This blog post explores how developers can tailor the AI assistant to provide accurate inline suggestions and contextual code understanding for their C# and C++ projects. You will learn how to leverage customizations to boost productivity, streamline development workflows, and unlock the full potential of Amazon Q Developer across your codebase.

Overview

Like many developers, I learned to code in C. Thirty years later, C# and C++ are both still among the top 10 most used programming languages. However, much of that code is proprietary and stored in private repositories, while Python, JavaScript, and Java dominate public repositories. Therefore, it is critical that I can customize my AI assistant with my private, proprietary code examples. Amazon Q Developer expanded its customization capabilities to include support for C# and C++, in addition to Python, Java, JavaScript, and TypeScript that it already supports.

If you caught my session at re:Invent 2024, Best practices for customizing Amazon Q Developer, you might remember me showcasing how to customize Amazon Q Developer using a Python-based MovieRepository example. With positive feedback from the Python developers, I want to bring that same level of customization to my C# and C++ developers. So, without further delay, let’s dive in and see how you can get the most out of Amazon Q Developer in your C# and C++ projects.

Inline suggestions

Let’s start by looking at how Amazon Q Developer can provide inline suggestions. I’ll use C# for this example. Take a look at Insert method of the MovieRepository class. The MovieRepository class supports basic create, read, update, and delete (CRUD) operations. Notice that the Insert method expects four fields for each movie: title, year, plot, and rating.

/// <summary>
/// Adds a movie to the table.
/// </summary>
/// <param name="title">The title of the movie.</param>
/// <param name="year">The release year of the movie.</param>
/// <param name="plot">The plot summary of the movie.</param>
/// <param name="rating">The quality rating of the movie.</param>
public async Task Insert(string title, int year, string plot, decimal rating)
{ ... }

When I use the default, non-customized, version of Amazon Q Developer, it does its best to help me out. However, you might notice a few errors in the suggestion on line 17 of the screenshot below. First, Amazon Q Developer has suggested a reference to a method named AddMovie, but the actual method in the MovieRepository class is named Insert. Second, Amazon Q Developer guessed three of the four parameters correctly – title, year, and rating, but suggested a director rather than plot. Third, the order of the parameters is not correct.

C# code showing a MovieDatabase namespace containing a Program class with a Main method. The code creates a MovieRepository instance and adds the movie "Titanic" to the database with director James Cameron, year 1997, and rating 7.8 using an async method.

Of course, I cannot fault Amazon Q Developer for these mistakes. It has never seen the MovieRepository, which is stored in a private repository. Now, let’s switch over to my customized version of Amazon Q Developer. Note that I have created a customization following the instructions in the Amazon Q Developer User Guide and the best practices discussed in my re:Invent talk. I simply activate the customization in my IDE.

A dialog box titled "Select a Customization" showing two options: "Amazon Q foundation (Default)" with the description "Receive suggestions from Amazon Q base model" and "amazon-q-developer-customization-demo" marked as "Connected" with "No description provided". The dialog has a back arrow, title, help icon, and close button in the header.

With the customization selected, Amazon Q Developer now understands the exact structure of my MovieRepository class. Look at the suggestion on line 17 of the following image. With the customization enabled, Amazon Q Developer has correctly suggested the method name, parameter names, and parameter order. In addition, it understands that MovieRepository is using Amazon DynamoDB behind the scenes. Finally, notice that this suggestion spans multiple lines, while the prior example was all on one line. Amazon Q Developer is formatting the code to match my team’s preferred style, with each parameter on a separate line, based on the examples it saw in my customization.

C# code showing a MovieDatabase namespace containing a Program class with a Main method. The code creates a MovieRepository instance and uses InsertAsync to add the movie "Titanic" to DynamoDB with details including the title, year 1997, a partial plot description, and rating of 7.8.

This is the power of customization: Amazon Q Developer is tailoring its suggestions to fit my codebase and preferences. The customization benefits don’t stop at inline suggestions. Let’s take a look at how Amazon Q Developer can assist me in chat, this time using a C++ example.

Chatting about code

In addition to inline suggestions, my customization is also available in the chat. Personally, I use a combination of inline suggestions and chat. I prefer the inline suggestions when I know the codebase and want to work faster. I prefer chat when I do not know the codebase well and I want Amazon Q Developer to provide additional context.

In the following example, I ask Amazon Q Developer – “How to I add movies to the C++ MovieRepository.” I should note that the customization is still enabled and that the single customization supports C# and C++ in addition to Python, Java, JavaScript, and TypeScript. I do not need to enable a different customization for each language.

Once again, Amazon Q Developer provides accurate information about the MovieRepository structure. In addition, the response includes additional instructions and multiple examples (though I only included one in the screenshot). Also, you may have noticed that Amazon Q Developer is a sci-fi fan. I’m not surprised.

A code snippet in C++ showing how to add a movie to the MovieRepository using the Insert method. The example adds "The Matrix" with its release year (1999), a brief plot description, and rating (8.7). The code includes error handling that outputs success or failure messages. The snippet appears to be part of a larger response explaining different ways to add movies to a repository.

But wait, there’s more! Amazon Q Developer has also read my README files. Therefore, it can answer questions about usage, installation, troubleshooting, and more. In this final example, I will ask Amazon Q Developer for help troubleshooting. Amazon Q Developer makes multiple suggestions (though I only included one in the screenshot) about potential issues and how to fix them.

Code example showing two methods for configuring AWS credentials in a C++ MovieRepository. The first option uses environment variables with export commands for AWS access keys. The second option shows the format for storing credentials in a ~/.aws/credentials file. This appears to be part of a troubleshooting guide addressing common AWS authentication issues.

The impact of customization on the inline suggestions and chat combine to keep me focused and in a state of flow.

Conclusion

I’m thrilled to have the ability to customize Amazon Q Developer for my C# and C++ projects. Whether I’m looking for inline suggestions or need help understanding my codebase through the chat feature, this tool has become an invaluable part of my development workflow. If you haven’t already, I’d highly encourage you to check out the Amazon Q Developer documentation and start leveraging the power of customization for your own projects.

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