Emacs can do this "out of the box". See Tags in the Emacs manual.

Here's what I did to make sure it works.

1. Got Emacs sources from https://github.com/emacs-mirror/emacs
2. Ran find . -iname "*.c" -or -iname "*.h" | xargs etags to create a TAGS table.
3. Added this TAGS table using M-x visit-tags-table.

Now I can put my cursor on optional_new_start in window.c, press M-. RET and end up on the appropriate line in window.h.

You can then press M-* to go back to the point you started from.

PS: It does not matter if variable and function names have underscores in them.

Emacs can do this "out of the box". See Tags in the manual. (Press C-h r m tags RET to read this section in Emacs.)

Here's what I did to make sure it works.

1. Got Emacs sources from https://github.com/emacs-mirror/emacs
2. Ran find . -iname "*.c" -or -iname "*.h" | xargs etags to create a TAGS table.
3. Added this TAGS table using M-x visit-tags-table.

Now I can put my cursor on optional_new_start in window.c, press M-. RET and end up on the appropriate line in window.h.

You can then press M-* to go back to the point you started from.

PS: It does not matter if variable and function names have underscores in them.

Emacs can do this "out of the box". See Tags in the Emacs manual.

Here's what I did to make sure you it works.

1. Got Emacs sources from https://github.com/emacs-mirror/emacs
2. Ran find . -iname "*.c" -or -iname "*.h" | xargs etags to create a TAGS table.
3. Added this TAGS table using M-x visit-tags-table.

Now I can put my cursor on optional_new_start in window.c, press M-. RET and end up on the appropriate line in window.h.

You can then press M-* to go back to the point you started from.

Emacs can do this "out of the box". See Tags in the Emacs manual.

Here's what I did to make sure it works.

1. Got Emacs sources from https://github.com/emacs-mirror/emacs
2. Ran find . -iname "*.c" -or -iname "*.h" | xargs etags to create a TAGS table.
3. Added this TAGS table using M-x visit-tags-table.

Now I can put my cursor on optional_new_start in window.c, press M-. RET and end up on the appropriate line in window.h.

You can then press M-* to go back to the point you started from.

PS: It does not matter if variable and function names have underscores in them.