main: ban fpos_t

[masatake]

fpos_t has caused making our code complicated.

Will ctags deal with files larger than sizeof(long)?
I think it will not.

So I would like to use only ftell/fseek, not together with fsetpos/fgetpos.

Anjuta-ctags took the way I like.

https://gitlab.gnome.org/Archive/anjuta/-/commit/91f5e7fe0a6e4d548f4888711cdaaf7bedab6f85
https://gitlab.gnome.org/Archive/anjuta/-/commit/0adbb5451148027bc6cb283acbfd98c5dc79aad0

What do you think?

[k-takata]

You may need to consider that long is 32 bits on Windows.
Windows has the 64-bit version of fseek:
https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/fseek-fseeki64?view=msvc-170
If we don't need to consider the files that are larger than 2 GB, simply using long should be okay.
Otherwise, the source code of Vim might be helpful:
https://github.com/vim/vim/blob/c0da540466c89e388e7a15a12bab2f9fc42d9671/src/vim.h#L384-L416
(MSWIN is defined inside Vim. Normally we can use _WIN32 instead. PROTO is used for the cproto command, so this can be ignored.)

[masatake]

@k-takata, thank you for the suggestion. Only about input, I think 2GB is large enough.
For output, 2GB is too small.

[k-takata]

Oh, I remember that we've already done this in readtag:

ctags/libreadtags/readtags.c

Lines 111 to 135 in 3547021

	static rt_off_t readtags_ftell(FILE *fp)
	{
	rt_off_t pos;
	#ifdef _WIN32
	pos = _ftelli64(fp);
	#else
	pos = ftell(fp);
	#endif
	return pos;
	}
	static int readtags_fseek(FILE *fp, rt_off_t pos, int whence)
	{
	int ret;
	#ifdef _WIN32
	ret = _fseeki64(fp, pos, whence);
	#else
	ret = fseek(fp, pos, whence);
	#endif
	return ret;
	}

[masatake]

Nice! We should reuse it.