• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 496
  • Last Modified:

Byte Swaping a structure

I would like to set data elements to a struction and then byte swap the entire structure.
The part that makes it difficult is the struction contains elements of diffrent sizes.  Below is an example of a data structure that uses shorts, ints, and chars all in the same structure.
I do not have to perform any word swapping just byte swapping.

Is there some inherent function in C++ like the _swab function that performs this.  If not does someone have an example of how to do this. Once the structure is swapped it will be written to a file.


#pragma pack(1)//eliminate padding in structs
typedef struct {
      short            IDMSAReportingMode : 2;
      short            IDMSAReportingSpare : 1;
      short            IDMSATimeFilter : 13;
      short            IDMSAMotionSpare : 4;
      short            IDMSAMotionFilter : 12;
      int            IDMStaleFilterDurationSpare : 13;
      int            IDMStaleFilterDuration : 19;
      int            IDMOldFilterDurationSpare : 13;
      int            IDMOldFilterDuration : 19;
      int            IDMPurgeFilterDurationSpare : 13;
      int            IDMPurgeFilterDuration : 19;
      short            IDMAutoResponseModeSpare : 6;
      short            IDMAutoResponseMode : 2;
      short            IDMChannelTransFlagSpare : 6;
      short            IDMChannelTransFlag : 2;
      char            IDMFSConfigFile[6];
      short            IDMTIInterfaceSpare : 6;
      short            IDMTIInterfaceNum : 2;
      short            IDMTICMSAPortNumSpare : 6;
      short            IDMTICMSAPortNum : 2;
      short            IDMFSInterfaceNumSpare : 6;
      short            IDMFSInterfaceNum : 2;
      short            IDMFSCMSAPortSpare : 6;
      short            IDMFSCMSAPort : 2;
      int            IDMEBC_OWN_URN_Spare : 9;
      int            IDMEBC_OWN_URN : 23;
      int            IDMMulticast_URN_Spare : 9;
      int            IDMMulticast_URN : 23;
      char            IDMTIPassword[8];
      short            IDMFIPRRegNetworkMonitoring : 1;
      short            IDMFIPRRegSystemCoord : 1;
      short            IDMFIPRRegSecurityMsg : 1;
      short            IDMFIPRRegFreetext : 1;
      short            IDMFIPRRegUnitRefQuery : 1;
      short            IDMFIPRRegInfoRequest : 1;
      short            IDMFIPRRegObserverMsnUpdate : 1;
      short            IDMFIPRRegMsgToObserver : 1;
      short            IDMFIPRRegAirborneFireMsn : 1;
      short            IDMFIPRRegBasicWeatherRprt : 1;
      short            IDMFIPRRegMaydayMsg : 1;
      short            IDMFIPRRegSpot_SaluteRprt : 1;
      short            IDMFIPRRegObstacleRprt : 1;
      short            IDMFIPRRegPosRprt : 1;
      short            IDMFIPRRegNBC3Rprt : 1;
      short            IDMFIPRRegREDCONRprt : 1;
      short            IDMFIPRRegThreatWarning : 1;
      short            IDMFIPRRegSitrep : 1;
      short            IDMFIPRRegMOPP : 1;
      short            IDMFIPRRegSupplyPointStatus : 1;
      short            IDMFIPRRegTaskMgmt : 1;
      short            IDMFIPRSpare : 11;
      char            IDMEBC_UTO[64];

} IDM_OPERATOR_CONFIG_TYPE;
0
LBoorn
Asked:
LBoorn
  • 3
1 Solution
 
jkrCommented:
>>Is there some inherent function in C++ like the _swab function that performs this

'_swab()' works like

/* SWAB.C illustrates:
 *      _swab
 */

#include <stdlib.h>
#include <stdio.h>

char from[] = "BADCFEHGJILKNMPORQTSVUXWZY";
char to[] =   "..........................";

void main()
{
    printf( "Before:\t%s\n\t%s\n\n", from, to );
    _swab( from, to, sizeof( from ) );
    printf( "After:\t%s\n\t%s\n\n", from, to );
}
0
 
jkrCommented:
BTW, as I can see, you don *NOT* want to use '_swab()' at all - if your goal is to put the above in non-intel byte order, just swapping the byte is not enough, you need to use the appropriate functions on the bitfield members.
0
 
jkrCommented:
OK, here we go

#include <winsock.h> // endianity support
#pragma comment ( lib, "ws2_32.lib")

typedef struct {
    short          IDMSA;
    int                     IDMFilter;
    short          IDMShort1;
    char           IDMFSConfigFile[6];
    short          IDMShort2;
    int            IDMInt;
    char           IDMTIPassword[8];
    short          IDMShort3;
    char          IDMEBC_UTO[64];

} IDM_OPERATOR_CONFIG_TYPE_HELPER;

IDM_OPERATOR_CONFIG_TYPE idm; // original struct
IDM_OPERATOR_CONFIG_TYPE_HELPER* p = &idm; // helper needed fow swapping

p->IDMSA= htons ( p->IDMSA);
p->IDMFilter = htonl ( p->IDMFilter);
p->IDMShort1 = htons ( p->IDMShort1);
p->IDMShort2 = htons ( p->IDMShort2);
p->IDMInt = htonl ( p->IDMInt);
p->IDMShort3 = htons ( p->IDMShort2);

This will avoid the byte swapping for the character members, which certainly is somethig you wouldn't want to happen :o)
0

Featured Post

Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.

  • 3
Tackle projects and never again get stuck behind a technical roadblock.
Join Now