C question - headers in mmaped files

[Martin Pool]

On  2 Apr 2003, Michael Still <mikal at stillhq.com> wrote:

> In addition to what everyone else said, lots of people solve this sort of
> problem with a struct and a union. Checkout this code which probably wont
> compile (pine needs a "compile my example" command):
> 
> typedef struct{
>   char magic[4];
>   int version;
>   float gronk;
> } dattype;
> 
> typedef union{
>   dattype data;
>   char * raw;
> } jpfile;
> 
> jpfile foo;
> foo->raw = mmap(...);
> 
> foo.data.magic[0] = 'J';
> foo.data.magic[1] = 'P';
> foo.data.magic[2] = 'F';
> foo.data.magic[3] = 'L';
> 
> ...etc...

Segmentation fault      (core dumped) 

I think a plain cast would be safer and nicer.  It would at least
prevent you writing 'JPFL' into a pointer.  And why introduce a new
datatype if you're only going to use it in place of a cast?

-- 
Martin