[Bug c/13078] New: sizeof returns incorrect 4 byte aligned value when structure contains integers and smaller types

[michaelcollins at ivorycity dot com]

Interesting and annoying bug... 
gcc version 3.2.3 Gentoo Linux 
 
The sizeof() operator returns the incorrect size of structures when they 
contain a mixture of integers and shorts or char types. 
 
sizeof() returns a 4 byte aligned size for the structure when the structure 
contains at least one integer and an odd number of shorts or chars 
 
ex1: 
struct a 
{ 
  int i; 
  short j; 
}; 
 
sizeof(struct a) is 8, it should be 6 
 
And it returns a 2 byte aligned size when a structure contains at least one 
short and and odd number of chars. 
 
Ex2: 
 
struct b 
{ 
  short i; 
  char j; 
}; 
 
sizeof( struct b ) is 4, it should be 3 
 
 
I understand why you might want 4 byte aligned values, but this has caused me 
mega bug headaches when writing binary files, since I end up more bytes than I 
intended and my opcode offsets get all fouled up. 
 
Here is some more code: 
 
struct 
try1 
{ 
  unsigned short a; 
}; 
 
struct 
try2 
{ 
  unsigned int   a; 
  unsigned short b; 
}; 
 
struct 
try3 
{ 
  unsigned int   a; 
  unsigned short b; 
  unsigned short c; 
}; 
 
struct 
try4 
{ 
  unsigned int   a; 
  unsigned short b; 
  unsigned short c; 
  unsigned short d; 
}; 
 
struct 
try5 
{ 
  unsigned int   a; 
  unsigned short b; 
  unsigned short c; 
  unsigned char  d; 
}; 
 
int 
main() 
{ 
  printf("Size %d my machine prints 2  should be 2\n", sizeof(struct try1)  ); 
  printf("Size %d my machine prints 8  should be 6\n", sizeof(struct try2)  ); 
  printf("Size %d my machine prints 8  should be 8\n", sizeof(struct try3)  ); 
  printf("Size %d my machine prints 12 should be 10\n", sizeof(struct try4) ); 
  printf("Size %d my machine prints 12 should be 9\n", sizeof(struct try5) ); 
}

-- 
           Summary: sizeof returns incorrect 4 byte aligned value when
                    structure contains integers and smaller types
           Product: gcc
           Version: 3.2.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: michaelcollins at ivorycity dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: gcc (GCC) 3.2.3 20030422
  GCC host triplet: (Gentoo Linux 1.4 3.2.3-r2, propolice)
GCC target triplet: x86


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13078