On Wed, 31 Aug 2022, Qing Zhao via Gcc-patches wrote:

> > How is level 3 (thus -fstrict-flex-array) interpreted when you specify 
> > -std=c89?  How for -std=gnu89?
> 
> 1. what’s the major difference between -std=c89 and -std=gnu89 on flexible array? (Checked online, cannot find a concrete answer on this).
> 	** my understanding is:   -std=c89 will not support any flexible array (neither [], [0], [1]), but -std=gnu89 will support [0] and [1], but not [].
>         Is this correct?

Flexible array members are supported in all C standard modes, since they 
don't affect the semantics of any valid pre-C99 program (only make valid 
programs that were previously erroneous).

With -std=c89 or -std=gnu89, -pedantic will give a warning "ISO C90 does 
not support flexible array members" and -pedantic-errors will change that 
to an error.

-- 
Joseph S. Myers
joseph@codesourcery.com