byte reordering macro (big/litte endian conversion between OS)

[apollo135]

Dear all,

Could someone please clarify and help with byte ordering macro (big/litte endian conversion)? I found thefollowinf macron on the internet but I have a doubt to use it ...
============
#if defined(BIG_ENDIAN) && !defined(LITTLE_ENDIAN)

#define htons(A) (A)
#define htonl(A) (A)
#define ntohs(A) (A)
#define ntohl(A) (A)

#elif defined(LITTLE_ENDIAN) && !defined(BIG_ENDIAN)

#define htons(A) ((((uint16)(A) & 0xff00) >> 8) | \
(((uint16)(A) & 0x00ff) << 8))
#define htonl(A) ((((uint32)(A) & 0xff000000) >> 24) | \
(((uint32)(A) & 0x00ff0000) >> 8) | \
(((uint32)(A) & 0x0000ff00) << 8) | \
(((uint32)(A) & 0x000000ff) << 24))
#define ntohs htons
#define ntohl htohl

#else

#error "Either BIG_ENDIAN or LITTLE_ENDIAN must be #defined, but not both."

#endif
==================

Should we use it as it is? if yes, why I am getting an error when I compile the program at this line : #error "Either BIG_ENDIAN or LITTLE_ENDIAN must be #defined, but not both." ? Is there any specific library should be included in program or something missing ...

If not, should the the part of program look like the following?
=========
#if defined(BIG_ENDIAN)

#define htons(A) (A)
#define htonl(A) (A)
#define ntohs(A) (A)
#define ntohl(A) (A)

#elif defined(LITTLE_ENDIAN)

#define htons(A) ((((uint16)(A) & 0xff00) >> 8) | \
(((uint16)(A) & 0x00ff) << 8))
#define htonl(A) ((((uint32)(A) & 0xff000000) >> 24) | \
(((uint32)(A) & 0x00ff0000) >> 8) | \
(((uint32)(A) & 0x0000ff00) << 8) | \
(((uint32)(A) & 0x000000ff) << 24))
#define ntohs htons
#define ntohl htohl

#endif
============

Any help woul be very appreciated and thank you in advance for your replies

[JosAH]

You're not supposed to include that file directly; there should be a 'wrapping' file,
defining these constants and you're supposed to include that one. Check your man
pages.

kind regards,

Jos

[apollo135]

You're not supposed to include that file directly; there should be a 'wrapping' file,
defining these constants and you're supposed to include that one. Check your man
pages.

kind regards,

Jos

-----------------------

Hi Jos,

Thanks a lot for your reply. You are right that is what I read on the internet but I couldn't find details on how to write and it is the first time that I am dealing with. I would be glad if you could explain more about or send me the usefull link.

Regards and thanks for your reply,
Azwaw

[apollo135]

-----------------------

Hi Jos,

Thanks a lot for your reply. You are right that is what I read on the internet but I couldn't find details on how to write and it is the first time that I am dealing with. I would be glad if you could explain more about or send me the usefull link.

Regards and thanks for your reply,
Azwaw

-------------

Hi Jos,

I tried also to use macros: htonl and ntohl as the variables exchanged between client and server are defined in double. But it does not work ... and here is a peace of code I wrote:

-------- client.cpp---
...
typedef struct SIM_DATA_IN{
// char svar_instg;
double svar_integ[2];
double svar_indl[5];
};
SIM_DATA_IN stus;
...
stus.svar_integ[0]=htonl(var);
stus.svar_integ[2]=htonl(mr);
...
stus.svar_indl[1]=htonl(GH);
....
stus.svar_indl[5]=htonl(DR);
....

if(sendto(sd,&stus,sizeof(&stus),0,(struct sockaddr *) &pin,sizeof(pin))) {
perror("write data");
exit(1);
}
.....

--------server.cpp-------
...
#define MAXBF 1024
....

typedef struct SIM_DATA_IN{
// char svar_instg;
double svar_integ[2];
double svar_indl[5];
};
SIM_DATA_IN stus;


if(recvfrom(sd,&stus,MAXBF,0,(struct sockaddr *) &pin,&fromSize)) {
perror("read data");
exit(1);
}
.....
...
*spn=ntohl(stus.svar_integ[0]);
*spm=ntohl(stus.svar_integ[1]);
...
*MB=ntohl(stus.svar_indl[0]);
...
*SB=ntohl(stus.svar_indl[5]);
....

================
Is this correct? if yes, it does not work ... I don't get the same data at the server side ... What is the matter then?

Regards and thanks for your reply,
Azwaw