2d array expression

[hraftery]

Out of the box, 2D fixed size arrays in C are displayed well in VSCode:

But as soon as that array is passed to a function and decays to a pointer, that ability is seemingly lost. Even if the C99 feature of specifying the dimensions with variables is used:

void func(int numRows, int numCols, double mat[numRows][numCols])

The default "simple expressions" interpreter gives up:

? mat
<not available>

By sheer bloody minded determination, I got the native interpreter to play ball:

?/nat *((double(*)[5][8]) mat)
{...}
[0] = {1, 1, 0, 1, 1, 1, 0, 63}
[1] = {1, 1, 0, 1, 1, 0, 1, 62}
[2] = {1, 1, 0, 0, 1, 0, 0, 36}
[3] = {1, 0, 1, 1, 0, 1, 0, 39}
[4] = {0, 1, 1, 0, 0, 0, 1, 35}

by basically subverting the ability to typecast as a 3D array, and print the first "row" (which is the whole 2D array). Gloriously then, I can use this in a Watch expression, which is nice.

The closest I got with simple expressions is only row by row:

? mat[0],[8]
{1, 1, 0, 1, 1, 1, 0, 63}
? mat[1],[8]
{1, 0, 1, 1, 1, 0, 63, 1}

But so far no way to retain the behaviour that's available before the array is passed to a function.

Is there a 2D array expression syntax, or am I perhaps using the wrong tool for the job (CodeLLDB or LLDB itself, noting the former is not focused on C necessarily)?

[vadimcn]

Look into LLDB formatters. You could start with a type summary, however, that gets you only a single line of text (well, if you include line breaks you might be able to get 2D view in tooltips).
If that is not enough, you could try to replicate the 2D matrix view via a synthetic provider, though I suspect won't be easy.
Other than that, you could also use codelldb web view API to render matrices.

Ah, also, I know of this VSCode extension for complex data visualization. There may be others.

[hraftery]

Thanks for the clear pointers. Very handy.

Just to set expectations I'm unlikely to pursue this. It was big learning lift for me to understand it well enough to document it. And having stumbled on the workaround in the course of doing so, I now have a searchable reference for when I next forget.

But I'd love to following along if anyone else does, or has other tips to share.