PackCC | PackCC is a packrat parser generator for C | Parser library

There is no problem with your use of $$, in the sense that the char * value stored in $$ by the word action is faithfully returned into val.

The problem is that the char* value is a pointer to dynamically-allocated memory, and by the time the parser returns that dynamically-allocated memory has already been freed. So the pointer returned into val is a dangling pointer, and by the time printf is called, the memory region has been been used for some other object.

The documention for PackCC, such as it is, does not go into any detail about its memory management strategy, so it's not really clear how long the $1 pointer in a rule is valid. I think it would be safest to assume that it is only valid until the end of the last action in the rule. But it is certainly not reasonable to assume that the pointer will outlast a call to pcc_parse. After all, the parser has no way to know that you have stored the pointer outside of the parser context. The parser cannot rely on the programmer to free capture strings produced during rules; having to free every capture, even the ones never used, would be a sever inconvenience. To avoid memory leaks, the parser therefore must free its capture buffers.

The problem is easy to see if you are able to use valgrind or some similar tool. (Valgrind is available for most Linux distributions and for OS X since v10.9.x. Other platforms might be supported.) Running your parser under valgrind produced the following error report (truncated):

The answer is very simple yet many people don't know this so I'm going to post the answer so that it can help someone out in the future.

I'm not sure if ctags allows for same name tags but it's irrelevant. What you can do is generate your own tags as explained in :help tags-file-format. This can be accomplished with a script containing less than 20 lines of code with a program like rip grep or you can use vimwiki plugin which implements this feature.

Here is an example of a simple tags file that jumps to bar:

Without looking more closely at the generated code, it would seem that the parser insists on reading the entire text into memory before executing any of the actions. That seems unnecessary for this grammar, and it is certainly not the way a typical generated lexical scanner would work. It's particularly odd since it seems like the generated scanner uses getchar to read one byte at a time, which is not very efficient if you are planning to read the entire file.

To be fair, you wouldn't be able to use ftell in a flex-generated scanner either, unless you forced the scanner into interactive mode. (The original AT&T lex, which also reads one character at a time, would give you reasonable value from ftell. But you're unlikely to find a scanner built with it anymore.)

Flex would give you the wrong answer because it deliberately reads its input in chunks the size of its buffer, usually 8k. That's a lot more efficient than character-at-a-time reading. But it doesn't work for interactive environments -- for example, where you are parsing directly from user input -- because you don't want to read beyond the end of the line the user typed.

You'll have to ask whoever maintains packcc what their intended approach for maintaining source position is. It's possible that they have something built in.

This looks like a bug in that version of the packcc parser generator. It is now fixed in master, so try upgrading.

Or you can simply ignore the warning as the type should indeed be int.

You'll need either:

• to pass the right number to :tag & co,
• or to use :tselect
• or to use a plugin that'll help distinguish/select the overload you're interested in (like my old lh-tags plugin)
• or a more modern solution like a LSP server: lately I've found coc+ccls to be quite nice as it'll know from the context which is the exact overload under the cursor, which is impossible with tag based solutions.

I don't know why that is, but it happened to me as well. I found a workaround that I cannot explain (user error? bug?), by removing these lines from the gtags.conf file (in the one for universal-ctags|setting to use Universal Ctags plug-in parser part):