unions of structs...

[kernel panic]

im trying to create a structure for peeling apart a 16b command word.. why doesn't this work??

struct __commandstruct
{
byte C0:1;
byte uu:4;
byte Ps:3;
byte timerval;
};

union
{
__commandstruct commandstruct;
long commandword;
};


i should then be able to get the elements like so..

comamandword= 0xffff;

commandstruct.CO=false
etc..


it no work like that?? as far as i can tell its of the txtbook..

!
!
\\\\\\/
[.] [.]
\
____
/ \
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This message was ported from CCS's old forum
Original Post ID: 6014

[kernel panic]

it seems nesting the struct inside the union works.. perhaps the compiler doesn't like previously defined typedefs inside of new typedefs..




:=im trying to create a structure for peeling apart a 16b command word.. why doesn't this work??
:=
:=struct __commandstruct
:={
:= byte C0:1;
:= byte uu:4;
:= byte Ps:3;
:= byte timerval;
:=};
:=
:=union
:={
:= __commandstruct commandstruct;
:= long commandword;
:=};
:=
:=
:=i should then be able to get the elements like so..
:=
:=comamandword= 0xffff;
:=
:=commandstruct.CO=false
:=etc..
:=
:=
:=it no work like that?? as far as i can tell its of the txtbook..
:=
:= !
:= !
:=\\\\\\/
:=[.] [.]
:= \
:= ____
:= / \
___________________________
This message was ported from CCS's old forum
Original Post ID: 6015

[Woody]

Your example code does not use typedef to define a new user type and therefore your union should look like this:-

union
{
struct __commandstruct commandstruct;
long commandword;
};

The following example shows two ways of defining the structure and overlay. Either method will work but using typedef's is usually easier.

/**********************************/
#include <16f876.h>

#pragma CASE

#define FIRST_METHOD
#ifdef FIRST_METHOD

#define DATA_OVERLAY_TYPE Datamap

typedef struct tagCommandstruct {
unsigned int C0:1;
unsigned int uu:4;
unsigned int Ps:3;
unsigned int timerval;
} Commandstruct;

/* Example 1 using newly defined type */
typedef union tagDatamap {
Commandstruct commandstruct;
long commandword;
} Datamap;

#else

#define DATA_OVERLAY_TYPE union tagDatamap

struct tagCommandstruct {
unsigned int C0:1;
unsigned int uu:4;
unsigned int Ps:3;
unsigned int timerval;
};

/* Example 2 using struct tagCommandstruct */
union tagDatamap {
struct tagCommandstruct commandstruct;
long commandword;
};

#endif

int main (void)
{
DATA_OVERLAY_TYPE v;

v.commandstruct.C0 = 1;
}

/************************************/

PS.
It's not a good idea to use identifiers starting underscore. I believe the ANSI standard for 'C' reserves identifiers starting with double underscore __ and underscore following by a capital letter. That's not to say user identifiers defined like this this will not work, but it could easily cause an obscure problem one day.
___________________________
This message was ported from CCS's old forum
Original Post ID: 6134