I have a little class/function detector in my .vimrc displaying, in my statusline, the python class/function my cursor currently is inside of. I am currently trying to adapt it for C++ source files, and am running into a pretty simple (?) regex (?) problem.

My function essentially works as follows:

  1. find the line number of the previous match of ::, but ignore std or cout:
let prev_class_line_number = search('\(std\)\@<!::\(cout\)\@!', 'bncW')
  1. From that line, return the \word before :::
let classname = matchstring(getline(prev_class_line_number), '\(\w\+\)::')

For example, within the following code block:

void MyClass::setSomething(int input) {
   // ...

my function returns "MyClass" (yay!).

I however run into issues with this type of code:

std::vector<int> MyClass::doSomethingElse(){
   // ...

where my function returns std instead of MyClass.

I spent a good amount of time getting my line-number-detection regexp to work (specifically, to not match std:: or ::cout), but I can't figure out how to get my second regexp to return 'MyClass'.

This looks like an incredibly simple problem and I'm sure I've been missing something. I searched into \zs/\ze, negative/positive lookahead/lookbehind, matchlist, but I haven't figured the right combination yet.

How do I extract the first word before a :: instance who is not std?

tl;dr: given the line std::foo bar::baz(), how can I return bar but not std?

1 Answer 1


The perfect solution is probably difficult to find in case of template class but for "simple" case maybe:


The first bit: ^\(\S\+\s+\)? match the return type if any (assuming it doesn't contain a space. For constructor and destructor you may have no return type and that is why we make it optional (\?)

The second bit: \(\w\+\) match the class name.

The third bit: ::\(\~\?\w\+\)\ze( match the method name.

The \ze( force the expression to match till the first parenthesis.

  • 1
    Sorry my first version lack the \ze( that forces the expression to search the parenthesis and makes that you can match the return type as the first word \S\+ (for "simple" case) Oct 21, 2022 at 19:19
  • Oooooh but that's even better if I use that with matchlist because I get in ONE SINGLE regexp both the class and function !? Thanks !
    – Feffe
    Oct 21, 2022 at 19:25
  • You are Welcome :-). If the solution fit the need don't forget to validate it ;-) Oct 21, 2022 at 19:30

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