Re: `string.unpack` 's bug in option `z`

[Dirk Laurie <dirk.laurie@...>]

Op Ma., 3 Sep. 2018 om 04:29 het actboy168 <actboy168@gmail.com> geskryf:

> Lua 5.3.5  Copyright (C) 1994-2018 Lua.org, PUC-Rio
>
> > print(string.unpack('z', 'ABC'))
> ABC     5
> This is not a zero-terminated string, so I think lua should raise an error.

You are right that 'ABC' is not a zero-terminated string, but I do not
agree that Lua should raise an error. The manual says 'All integral
options check overflows; ... string.unpack checks whether the read
value fits in a Lua integer.' There is no risk of overflow here, so an
error should not be raised, and the manual almost says so: 'Options
"c" and "z" are not aligned'.

The string pack/unpack routines are taken from Roberto's 'struct'
library http://www.inf.puc-rio.br/~roberto/struct/, which has been in
existence for at least six years (timestamp on the makefile).

BTW that library is a beautiful example of how to write C API code
that compiles on all Lua versions from 5.0 to 5.4 with only this
version-dependent test:

#if (LUA_VERSION_NUM >= 502)
#define luaL_register(L,n,f)    luaL_newlib(L,f)
#endif