[ILUG] round and drand48

[Pádraig Brady]

David Malone wrote:
>> You should not use the internal flags as you noted.
>> Instead #define _XOPEN_SOURCE in addition to the -std=c99 flag
>> For details on these macros see: info libc "feature test macros"
> 
> Ah - that works. It also works with -D_XOPEN_SOURCE on the command
> line (-D__USE_XOPEN doesn't 'cos I think it gets redefined by gcc
> or glibc internally later).
> 
>> An alternative is just to use the -std=gnu99 flag
> 
> Does that mean "the c99 language, plus any libraries and headers I
> have installed"? I guess this also allows GNU extensions to the C
> language?

-std=gnu99 ≡ -std=c99 -D_GNU_SOURCE

I generally put #define _GNU_SOURCE at the top of all
my C programs that require it (i.e. most of them).

> Is it documented anywhere what functions/macros depend on what
> _*_SOURCE, or do you just have to read the header files to find
> out? For example, I've just discovered that I also need -D_BSD_SOURCE
> in order to get random() and srandom(), but this isn't obvious (to
> me) from the glibc man pages.

Well it's documented correctly in my version of man pages.
You can browse or download the latest versions here:
http://www.kernel.org/doc/man-pages/

Note since you now need both _BSD_SOURCE and _XOPEN_SOURCE
I suggest you just define _GNU_SOURCE for simplicity.

Pádraig.