list changed function names or signatures with git diff (c++)

Question

I'm working on a git diff parser. The main task is to find all changed function signatures. Sometimes in the chunk line with @@@ .... @@@ contains these information but sometimes not. Last time I changed in greet() cout message and it is visible on first image as changed line and it is correct, but above in @@@... line appears "void functOne() {" and that is not changed. The second picture is about a dummy cpp source code to test git diff.

The main questions are
How can I list all changed function's signatures?
Why sometimes appears unchanged function name ?
Why sometimes doesn't appears any function name/signature in line with @@@.... ?

Answer 1

Sometimes in the chunk line with @@@ .... @@@

Git calls this a hunk header (after other diff software that also calls it that).

... contains [the function name] but sometimes not.

What Git puts in the function section of a diff hunk header is produced by matching earlier lines against a particular regular expression, as described in the gitattributes documentation under xfuncname (search for that string). But note that this is a regular expression, and regular expressions are inherently less capable than parsers; there will always exist valid C++ constructs that can be parsed, but not recognized by some regular expression you can write.

If Git's built in C++ xfuncname pattern is not adequate for your use, you can write your own pattern. But it's always going to be limited because regular expressions can only recognize regular languages (these are CS-theoretical or informatics terms, not to be interpreted as ordinary English language; for more, see, e.g., Regular vs Context Free Grammars).