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andreasfertig/cppinsights

★ 4,492C++Audience · developerComplexity · 3/5LicenseSetup · hard

TLDR

C++ Insights shows you the hidden code your compiler generates from modern C++ features, turning range-for loops, lambdas, and auto-generated class methods into explicit, readable C++ so you can see exactly what the compiler does with your code.

Mindmap

mindmap
  root((cppinsights))
    What it does
      Expands C++ syntax
      Shows compiler output
      Stays valid C++ code
    Key features
      Range-for expansion
      Lambda class view
      Auto-generated methods
    Usage
      Browser tool online
      Local Clang build
    Standards
      C++11 to C++23
    Audience
      C++ learners
      C++ teachers
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Code map

Detail Auto

An interactive map of this repo's files and how they connect — its source is parsed live in your browser. Click Visualize to build it.

filefunction / class

Things people build with this

USE CASE 1

Visualize what a range-based for loop expands to so you understand how the compiler iterates under the hood.

USE CASE 2

See the hidden constructors and operators your compiler auto-generates for a class, to catch unexpected copies or moves.

USE CASE 3

Inspect how a lambda is represented as a class internally to understand closure capture behavior.

USE CASE 4

Use as a teaching aid when explaining C++ to students who want to see the language's hidden mechanics.

Tech stack

C++Clang

Getting it running

Difficulty · hard Time to first run · 5min

Try instantly in the browser at cppinsights.io, local build requires a Clang installation.

MIT license, use, copy, modify, and distribute freely for any purpose, including commercial, with no restrictions beyond keeping the copyright notice.

In plain English

C++ Insights is a developer tool that translates C++ source code into a more expanded form that shows what the compiler actually does with your code when it compiles it. In other words, you give it a C++ file and it gives back a version of that file with all the hidden operations made explicit and visible. For example, when you write a simple class in C++, the compiler automatically generates several helper functions (like constructors and assignment operators) that you never wrote. C++ Insights rewrites your code to show those generated functions in place. When you write a range-based for-loop, a modern C++ convenience, it shows you the older, more verbose version of the loop that the compiler actually processes. When you write a lambda (an inline, anonymous function), it shows the class structure that represents that lambda internally. The tool was created as a teaching aid. The author found that existing ways to see compiler internals, such as looking at assembly output or the compiler's internal syntax tree, were hard for students to read because they are not in the same language that developers write. C++ Insights stays in C++, producing output that is still valid, compilable C++ code (where possible). You can try it directly in the browser at cppinsights.io without installing anything. For local use, you build it from source, the build process requires a Clang installation because the tool is built on top of Clang's internal libraries. It runs on Linux, macOS, and Windows, with specific build notes for each platform in the repository. The project supports code written with modern C++ standards from C++11 through C++23. It is open source under the MIT license and supported through Patreon. The author has given talks about it, and links to slides and videos are included in the README.

Copy-paste prompts

Prompt 1
I have this C++ class with a copy constructor, show me what the compiler-generated move constructor and copy-assignment operator would look like in explicit form, as if cppinsights had expanded it.
Prompt 2
Transform this range-based for loop into its expanded form showing the iterator calls, begin, end, and increment steps explicitly.
Prompt 3
I wrote a lambda that captures two variables by value. Show me the equivalent struct with an operator() and captured member variables that the compiler actually creates internally.
Prompt 4
Explain which modern C++ features cppinsights can make visible and how to try them in the browser without installing anything.
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