Hi Simeon,

 SC> Why is #pragma pack(1) required? And when should it
 SC> solve problems. As I say, I'm having no problems
 SC> without it.

There are a lot of pointers to functions in the _msgapi structure, which are
accessed by macros. If these are not aligned correctly, some api calls will
call a garbage pointer. Not all calls depend on this, but if the structure is
not packed properly you will have problems (i.e. traps, segment violations) at
some point.

It could be that EMX has changed it's default behaviour and is packing the
structures already, if you want to check, do a test program and look at the
value that sizeof(_msgapi) returns, and compare it to the size you get by
counting up the individual data members.

e.g. (from msgapi.h)

struct _msgapi {
 ...
 ...
  byte locked;                    /* Base is locked from use by other tasks */
  byte isecho;                    /* Is this an EchoMail area?              */

  struct _apifuncs
  {
    sword  (MAPIENTRY *CloseArea)(HAREA mh);

If this function is called, and the structure is not byte packed, it will
trap since the MSGAPI.DLL has to assume the offset of the function pointer
is where it expects it to be. With #pragma pack(1) active, the preceding
byte members will take up two bytes in the structure, with the default
packing they will take up 8 bytes, changing the offset of the function
pointer...

    - Geoff



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