Comments

• OSR_Community_User Member Posts: 110,217

  April 2000

  Lookup the pragma directive "#pragma pack " in the SDK
  
  Rohitab Batra
  [email protected]
  http://www.opengroup.org
  ------------------------------------------
  f u cn rd ths u cn gt a gd jb n cmptr pgmg
  
  
  -----Original Message-----
  From: Rakesh Shrivastava
  Sent: Saturday, April 29, 2000 2:51 PM
  To: NT Developers Interest List
  Subject: [ntdev] Byte Alignment
  
  
  Hello All,
  
  Does anybody know how to make the settings for the BYTE ALIGNMENT /PACKING
  for the structures.
  If yes, what are the settings for it.??
  
  The problem we are facing is
  
  typedef struct
  {
  unsigned char VAR1[3];
  }A;
  
  typedef struct
  {
  A a; // 3- BYTE SIZE
  unsigned int VAR2:8; // 1- BYTE SIZE
  unsigned int VAR3:16; // 2- BYTE SIZE
  }B;
  
  The sizeof (A) comes out to be 3
  and sizeof(B) comes out to be 7 (instead of 6).
  
  This is because the VC compiler stuffs a byte after the first structure A.
  Is there any settings for the alignment etc. to solve this .
  
  Thanks
  
  Rakesh Shrivastava
  DCM Tech
  New Delhi
  
  
  
  
  
  
  
  
  
  ---
  You are currently subscribed to ntdev as: [email protected]
  To unsubscribe send a blank email to $subst('Email.Unsub')

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• OSR_Community_User Member Posts: 110,217

  April 2000

  From the VC docs:
  
  pack
  #pragma pack( [ n] )
  
  Specifies packing alignment for structure and union members. Whereas the
  packing alignment of structures and unions is set for an entire translation
  unit by the /Zp option, the packing alignment is set at the data-declaration
  level by the pack pragma. The pragma takes effect at the first structure or
  union declaration after the pragma is seen; the pragma has no effect on
  definitions.
  
  When you use #pragma pack(n), where n is 1, 2, 4, 8, or 16, each structure
  member after the first is stored on the smaller member type or n-byte
  boundaries. If you use #pragma pack without an argument, structure members
  are packed to the value specified by /Zp. The default /Zp packing size is
  /Zp8.
  
  Jim
  
  -----Original Message-----
  From: [email protected]
  [mailto:[email protected]]On Behalf Of [email protected]
  Sent: Saturday, April 29, 2000 2:21 AM
  To: NT Developers Interest List
  Subject: [ntdev] Byte Alignment
  
  
  Hello All,
  
  Does anybody know how to make the settings for the BYTE ALIGNMENT /PACKING
  for the structures.
  If yes, what are the settings for it.??
  
  The problem we are facing is
  
  typedef struct
  {
  unsigned char VAR1[3];
  }A;
  
  typedef struct
  {
  A a; // 3- BYTE SIZE
  unsigned int VAR2:8; // 1- BYTE SIZE
  unsigned int VAR3:16; // 2- BYTE SIZE
  }B;
  
  The sizeof (A) comes out to be 3
  and sizeof(B) comes out to be 7 (instead of 6).
  
  This is because the VC compiler stuffs a byte after the first structure A.
  Is there any settings for the alignment etc. to solve this .
  
  Thanks
  
  Rakesh Shrivastava
  DCM Tech
  New Delhi
  
  
  
  
  
  
  
  
  
  ---
  You are currently subscribed to ntdev as: [email protected]
  To unsubscribe send a blank email to $subst('Email.Unsub')

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• OSR_Community_User Member Posts: 110,217

  April 2000

  Or you can use compiler independent method:
  
  #include "pshpackX.h" where X is required alignment (e.g. 1, 2, 4,
  ...)
  #include "poppack.h"
  
  These include files come with Platform SDK and for example NTIFS.H uses
  them.
  
  > -----P?vodn? zpr?va-----
  > Od: [email protected] [SMTP:[email protected]]
  > Odesl?no: 29. dubna 2000 11:51
  > Komu: NT Developers Interest List
  > P?edm?t: [ntdev] RE: Byte Alignment
  >
  > Lookup the pragma directive "#pragma pack " in the SDK
  >
  > Rohitab Batra
  > [email protected]
  > http://www.opengroup.org
  > ------------------------------------------
  > f u cn rd ths u cn gt a gd jb n cmptr pgmg
  >
  >
  > -----Original Message-----
  > From: Rakesh Shrivastava
  > Sent: Saturday, April 29, 2000 2:51 PM
  > To: NT Developers Interest List
  > Subject: [ntdev] Byte Alignment
  >
  >
  > Hello All,
  >
  > Does anybody know how to make the settings for the BYTE ALIGNMENT /PACKING
  > for the structures.
  > If yes, what are the settings for it.??
  >
  > The problem we are facing is
  >
  > typedef struct
  > {
  > unsigned char VAR1[3];
  > }A;
  >
  > typedef struct
  > {
  > A a; // 3- BYTE SIZE
  > unsigned int VAR2:8; // 1- BYTE SIZE
  > unsigned int VAR3:16; // 2- BYTE SIZE
  > }B;
  >
  > The sizeof (A) comes out to be 3
  > and sizeof(B) comes out to be 7 (instead of 6).
  >
  > This is because the VC compiler stuffs a byte after the first structure A.
  > Is there any settings for the alignment etc. to solve this .
  >
  > Thanks
  >
  > Rakesh Shrivastava
  > DCM Tech
  > New Delhi
  >
  >
  >
  >
  >
  >
  >
  >
  >
  > ---
  > You are currently subscribed to ntdev as: [email protected]
  > To unsubscribe send a blank email to $subst('Email.Unsub')
  >
  > ---
  > You are currently subscribed to ntdev as: [email protected]
  > To unsubscribe send a blank email to $subst('Email.Unsub')

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• Mark_Shnaider Member Posts: 95

  April 2000

  Try:
  #pragma pack(1)
  typedef struct
  {
  unsigned char VAR1[3];
  }A;
  #pragma pack()
  Mark
  
  [email protected] wrote:
  
  > Hello All,
  >
  > Does anybody know how to make the settings for the BYTE ALIGNMENT /PACKING
  > for the structures.
  > If yes, what are the settings for it.??
  >
  > The problem we are facing is
  >
  > typedef struct
  > {
  > unsigned char VAR1[3];
  > }A;
  >
  > typedef struct
  > {
  > A a; // 3- BYTE SIZE
  > unsigned int VAR2:8; // 1- BYTE SIZE
  > unsigned int VAR3:16; // 2- BYTE SIZE
  > }B;
  >
  > The sizeof (A) comes out to be 3
  > and sizeof(B) comes out to be 7 (instead of 6).
  >
  > This is because the VC compiler stuffs a byte after the first structure A.
  > Is there any settings for the alignment etc. to solve this .
  >
  > Thanks
  >
  > Rakesh Shrivastava
  > DCM Tech
  > New Delhi
  >
  > ---
  > You are currently subscribed to ntdev as: [email protected]
  > To unsubscribe send a blank email to $subst('Email.Unsub')

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• Gregory_G._Dyess Member - All Emails Posts: 386

  May 2000

  The long answer is this:
  #pragma pack( push, <Name>, <Packing size>)
  and to undo it/return to default:
  #pragma pack( pop, <Name> )
  
  
  Look up #pragma pack in the docs and it will explain the optional parameters
  shown above.
  
  Greg
  
  -----Original Message-----
  From: [email protected]
  [mailto:[email protected]]On Behalf Of [email protected]
  Sent: Saturday, April 29, 2000 4:21 AM
  To: NT Developers Interest List
  Subject: [ntdev] Byte Alignment
  
  
  Hello All,
  
  Does anybody know how to make the settings for the BYTE ALIGNMENT /PACKING
  for the structures.
  If yes, what are the settings for it.??
  
  The problem we are facing is
  
  typedef struct
  {
  unsigned char VAR1[3];
  }A;
  
  typedef struct
  {
  A a; // 3- BYTE SIZE
  unsigned int VAR2:8; // 1- BYTE SIZE
  unsigned int VAR3:16; // 2- BYTE SIZE
  }B;
  
  The sizeof (A) comes out to be 3
  and sizeof(B) comes out to be 7 (instead of 6).
  
  This is because the VC compiler stuffs a byte after the first structure A.
  Is there any settings for the alignment etc. to solve this .
  
  Thanks
  
  Rakesh Shrivastava
  DCM Tech
  New Delhi
  
  
  
  
  
  
  
  
  
  ---
  You are currently subscribed to ntdev as: [email protected]
  To unsubscribe send a blank email to $subst('Email.Unsub')

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• OSR_Community_User Member Posts: 110,217

  May 2000

  > Does anybody know how to make the settings for the BYTE ALIGNMENT /PACKING
  > for the structures.
  
  #pragma pack(1)
  - (in the source, surely) turns off alignment.
  #pragma pack()
  - turns it back on.
  
  Max

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