union issue

[Andrew Haley]

Mihai Don?u writes:

 > I have a "tiny" problem with gcc (or a certain standard
 > that did not show in my grep results). Given the sample code
 > below:
 > 
 > #include <stdio.h>
 > #include <stdint.h>
 > 
 > #define __PACKED __attribute__((packed))
 > 
 > typedef struct _type1_t {
 >     uint32_t field1:31;
 >     uint32_t field2:1;
 > } __PACKED type1_t;
 > 
 > typedef struct _type2_t {
 >     union {
 >         uint32_t field1:31;
 >         uint32_t field2:15;
 >     };
 >     uint32_t field3:1;
 > } __PACKED type2_t;
 > 
 > int main( void )
 > {
 >     type1_t a;
 >     type2_t b;
 > 
 >     printf( "%d %d\n", ( int )sizeof( a ), ( int )sizeof( b ) );
 > 
 >     return 0;
 > }
 > 
 > which (as some of you might have already guessed) gives me:
 > 
 > mihai@mdontu-l:~$ gcc test.c
 > mihai@mdontu-l:~$ ./a.out
 > 4 5
 > 
 > is there any way to instruct gcc not to pack the union into a dword?

I've read this three times now and I still don't understand your
question.  You declare a packed struct, but you don't want it to be
packed?  So don't declare it packed, then.  But that can't be what you
really meant.

Andrew.