Question

using grep, vim’s grep, or another unix shell command, I’d like to find the functions in a large cpp file that contain a specific word in their body.

In the files that I’m working with the word I’m looking for is on an indented line, the corresponding function header is the first line above the indented line that starts at position 0 and is not a ‘{‘.

For example searching for JOHN_DOE in the following code snippet

int foo ( int arg1 ) 
{
    /// code 
}
void bar ( std::string arg2  )
{
    /// code
    aFunctionCall( JOHN_DOE );
    /// more code
}

should give me

void bar ( std::string arg2  )

The algorithm that I hope to catch in grep/vim/unix shell scripts would probably best use the indentation and formatting assumptions, rather than attempting to parse C/C++.

Thanks for your suggestions.

Answer 1

As far as I know, this can’t be done. Here’s why:

First, you have to search across lines. No problem, in vim adding a _ to a character class tells it to include new lines. so {_.*} would match everything between those brackets across multiple lines.

So now you need to match whatever the pattern is for a function header(brittle even if you get it to work), then , and here’s the problem, whatever lines are between it and your search string, and finally match your search string. So you might have a regex like

/^\(void \+\a\+ *(.*)\)\_.*JOHN_DOE

But what happens is the first time vim finds a function header, it starts matching. It then matches every character until it finds JOHN_DOE. Which includes all the function headers in the file.

So the problem is that, as far as I know, there’s no way to tell vim to match every character except for this regex pattern. And even if there was, a regex is not the tool for this job. It’s like opening a beer with a hammer. What we should do is write a simple script that gives you this info, and I have.

fun! FindMyFunction(searchPattern, funcPattern)
  call search(a:searchPattern)
  let lineNumber = line(".")
  let lineNumber = lineNumber - 1
  "call setpos(".", [0,  lineNumber, 0, 0])

  let lineString = getline(lineNumber)
  while lineString !~ a:funcPattern
    let lineNumber = lineNumber - 1
    if lineNumber < 0
      echo "Function not found :/"
    endif
    let lineString = getline(lineNumber)
  endwhile

  echo lineString

endfunction

That should give you the result you want and it’s way easier to share, debug, and repurpose than a regular expression spit from the mouth of Cthulhu himself.