Re: unique identifiers for guard macros

[red floyd]

Ulrich Eckhardt wrote:
> Angel Tsankov wrote:
> > Can someone recommend a way to create "unique" identifiers for use 
> > in guard macros: 
> >
> > #if !defined (UNIQUE_GUARD)
> > #define UNIQUE_GUARD
>
> As you said, the most important thing is to not collide with any existing
> one. The advise to use a GUID is a good one, another good one is to just
> use the date when the file is started. I always leave a generic prefix
> like the module and the filename in uppercase (just in case I need to
> identify where it's coming from). 
>
> BTW: you asked for a GUID tool - depending on the  system you have, you
> don't need one, on most unixoid systems you can do this:
>
>   dd if=/dev/urandom count=1 bs=10 | md5sum 
>
> This reads ten bytes from a random-number generator and computes their MD5
> hash - should be sufficiently unique. ;)

Oh, that's a GOOD one!  I hadn't thought of that!

$ dd if=/dev/urandom count=1 bs=10 2> /dev/null | md5sum
d3474a0dc64708f0fe72817980f7faf5 *-

#ifndef FILE_H_d3474a0dc64708f0fe72817980f7faf5
#define FILE_H_d3474a0dc64708f0fe72817980f7faf5
// yada yada yada
#endif // include guard for file.h