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gcc2.95.2-2: #pragma pack(0) ??
- To: cygwin at sourceware dot cygnus dot com
- Subject: gcc2.95.2-2: #pragma pack(0) ??
- From: John Daniel Doucette <john dot doucette at jjmackay dot ca>
- Date: Wed, 20 Sep 2000 12:40:48 -0300
Hello,
I am doing unit testing on a PC of some embedded system software. I needed
to find a way of ensuring a group of structures were packed (1 byte
alignment). I didn't want to use -fpack-struct because it would cause
system structures to be packed as well whic hseemed a little dangerous to
me. __attribute__ ((packed)) would have to be placed with each of the
many structures which would involve modifying my tested source. I ended
up using #pragma pack(1), then including the header file, then #pragma
pack(0). Pack(0) is supposed to reset the structure packing back to
whatever the gcc default is (GNU gcc manual), however it gives you a
compiler error.
warning: Alignment must be a small power of two, not 0, in #pragma pack
warning: malformed `#pragma pack'
Can I assume that on a Win95 PC the default aligment is 4 byte? I ended up
using #pragma pack(4) at the end of the structures instead of
pack(0). See below for cygcheck output.
i.e.
header.h
=======
struct s
{
char ch;
long i;
}
struct r
{
char b;
char c;
long l;
}
source.c
=======
#pragma pack(1)
#include "header.h"
#pragma pack(4)
Cygnus Win95/NT Configuration Diagnostics
Current System Time: Wed Sep 20 14:13:19 2000
Win95 Ver 4.0 build 67109975 B
Path: /cygdrive/c/WINDOWS
/cygdrive/c/WINDOWS/COMMAND
/cygdrive/c/BC5/BIN
/cygdrive/c/RCS/BINNT
/cygdrive/c/DAP
/cygdrive/c/PKWARE
/cygdrive/c/UTILITY
/cygdrive/c/DOS
/cygdrive/c/BP/BIN
/cygdrive/c/BITWARE
/cygdrive/c/IAR/EXE
/cygdrive/c/IAR/INC
/usr/bin
/cygdrive/c/JJMACKAY/MET_TALK
/cygdrive/c/JJMACKAY/UTILITY
/cygdrive/c/PROGRA~1/ULTRAE~1
SysDir: C:\WINDOWS\SYSTEM
WinDir: C:\WINDOWS
!C: = `C:\Program Files\Netscape\Communicator\Program'
!D: = `D:\src\working\epurse\UnitTest\otproto'
TMP = `/cygdrive/c/WINDOWS/TEMP'
TEMP = `/cygdrive/c/WINDOWS/TEMP'
PROMPT = `$p$g'
WINBOOTDIR = `C:\WINDOWS'
COMSPEC = `C:\WINDOWS\COMMAND.COM'
CLASSPATH = `C:\Program Files\PhotoDeluxe 2.0\AdobeConnectables'
LOGNAME = `JohnDoucette'
TZ = `AST'
GEMPLUS_LIB_PATH = `C:\WINDOWS\GEMPLUS'
WINDIR = `C:\WINDOWS'
BLASTER = `A220 I5 D1 H5 P330 T6'
CMDLINE = `cygcheck -s -v -r'
TERM = `cygwin'
HKEY_CURRENT_USER\Software\Cygnus Solutions
HKEY_CURRENT_USER\Software\Cygnus Solutions\Cygwin
HKEY_CURRENT_USER\Software\Cygnus Solutions\Cygwin\mounts v2
(default) = `/cygdrive'
cygdrive flags = 0x00000020
HKEY_CURRENT_USER\Software\Cygnus Solutions\Cygwin\mounts v2\/
(default) = `C:/cygwin'
flags = 0x00000000
HKEY_CURRENT_USER\Software\Cygnus Solutions\Cygwin\mounts v2\/usr/bin
(default) = `C:/cygwin/bin'
flags = 0x00000000
HKEY_CURRENT_USER\Software\Cygnus Solutions\Cygwin\mounts v2\/usr/lib
(default) = `C:/cygwin/lib'
flags = 0x00000000
HKEY_CURRENT_USER\Software\Cygnus Solutions\Cygwin\Program Options
HKEY_LOCAL_MACHINE\SOFTWARE\Cygnus Solutions
HKEY_LOCAL_MACHINE\SOFTWARE\Cygnus Solutions\Cygwin
HKEY_LOCAL_MACHINE\SOFTWARE\Cygnus Solutions\Cygwin\mounts v2
a: fd N/A N/A
c: hd FAT32 3092Mb 40% CP UN JOHN_C
d: hd FAT32 4102Mb 54% CP UN JOHN_D
e: fd N/A N/A
f: cd CDFS 622Mb 100% CP Audio CD
g: net FAT32 2047Mb 0% CP UN DRIVE_C
j: net FAT32 2047Mb 0% CP UN DRIVE_C
C:\cygwin\bin /usr/bin user textmode
C:\cygwin\lib /usr/lib user textmode
C:\cygwin / user textmode
Found: C:\cygwin\bin\bash.exe
Found: C:\cygwin\bin\cat.exe
Found: c:\BC5\BIN\cpp.exe
Found: C:\cygwin\bin\cpp.exe
Warning: c:\BC5\BIN\cpp.exe hides C:\cygwin\bin\cpp.exe
Found: c:\WINDOWS\COMMAND\find.exe
Found: C:\cygwin\bin\find.exe
Warning: c:\WINDOWS\COMMAND\find.exe hides C:\cygwin\bin\find.exe
Found: C:\cygwin\bin\gcc.exe
Found: C:\cygwin\bin\gdb.exe
Found: C:\cygwin\bin\ld.exe
Found: C:\cygwin\bin\ls.exe
Found: c:\BC5\BIN\make.exe
Found: c:\UTILITY\make.exe
Warning: c:\BC5\BIN\make.exe hides c:\UTILITY\make.exe
Found: C:\cygwin\bin\sh.exe
385k 1998/05/01 C:\WINDOWS\SYSTEM\cygwinb19.dll - os=4.0 img=1.0 sys=4.0
"cygwinb19.dll" v0.0 ts=1998/3/11 0:04
83k 2000/06/11 C:\cygwin\bin\cygitcl30.dll - os=4.0 img=1.0 sys=4.0
"cygitcl30.dll" v0.0 ts=2000/6/11 3:34
35k 2000/06/11 C:\cygwin\bin\cygitk30.dll - os=4.0 img=1.0 sys=4.0
"cygitk30.dll" v0.0 ts=2000/6/11 3:34
402k 2000/06/11 C:\cygwin\bin\cygtcl80.dll - os=4.0 img=1.0 sys=4.0
"cygtcl80.dll" v0.0 ts=2000/6/11 3:30
5k 2000/06/11 C:\cygwin\bin\cygtclpip80.dll - os=4.0 img=1.0 sys=4.0
10k 2000/06/11 C:\cygwin\bin\cygtclreg80.dll - os=4.0 img=1.0 sys=4.0
"cygtclreg80.dll" v0.0 ts=2000/6/11 3:30
639k 2000/06/11 C:\cygwin\bin\cygtk80.dll - os=4.0 img=1.0 sys=4.0
"cygtk80.dll" v0.0 ts=2000/6/11 3:34
586k 2000/08/04 C:\cygwin\bin\cygwin1.dll - os=4.0 img=1.0 sys=4.0
"cygwin1.dll" v0.0 ts=2000/8/4 0:53
Cygwin DLL version info:
dll major: 1001
dll minor: 4
dll epoch: 19
dll bad signal mask: 19005
dll old termios: 5
api major: 0
api minor: 26
shared data: 3
dll identifier: cygwin1
mount registry: 2
cygnus registry name: Cygnus Solutions
cygwin registry name: Cygwin
program options name: Program Options
cygwin mount registry name: mounts v2
build date: Thu Aug 3 20:53:46 EDT 2000
CVS tag: cygwin-1-1-4
shared id: cygwin1S3
Use -h to see help about each section
==================================
John Daniel Doucette, Sr. Software Designer
J. J. MacKay Canada Limited
Halifax R & D Office
1046 Barrington Street, 1st Floor
Halifax, Nova Scotia
Canada
B3H 2R1
Phone 902.423.7727 x22
Fax 902.422.8108
Internet www . jjmackay . ca
Email john . doucette @ jjmackay . ca
==================================
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