Show HN: Cdecl-dump - represent C declarations visually
3 comments
·December 8, 2025coherentpony
I don’t understand what the visualisation screenshot in the README is trying to communicate to me.
bluetomcat
It starts from the identifier. At every stage, it outputs a sub-expression which is the “mirrored use” and corresponds to the boxed representation below it. When it reaches the top of the expression, it prints the final type of the expression which is the lone specifier-qualifier list.
As per the screenshot, “arr” is an array of 4 elements. Consequently, “arr[0]” is an array of 8 elements. Then, “arr[0][0]” is a pointer. And so on, until we arrive at the specifier-qualifier list.
pcfwik
Since this is about C declarations: for anyone who (like me) had the misfortune of learning the so-called "spiral rule" in college rather than being taught how declarations in C work, below are some links that explain the "declaration follows use" idea that (AFAIK) is the true philosophy behind C declaration syntax (and significantly easier to remember/read/write).
TL;DR: you declare a variable in C _in exactly the same way you would use it:_ if you know how to use a variable, then you know how to read and write a declaration for it.
https://eigenstate.org/notes/c-decl https://news.ycombinator.com/item?id=12775966
A small tool that parses C declarations and outputs a simple visual representation at each stage, as it encounters arrays, pointers or functions.
The program uses a table-driven lexer and a hand-written, shift-reduce parser. No external dependencies apart from the standard library.