Any Method to Determine Endianness at Compile Time ?

[perry.yuan]

How could I determine the endianness of my compile environment at
compile time, instead of run time? I need a macro ("some_expressi on"),
i.e.

#if some_expression
#define TARGET_IS_LITTL E_ENDIAN
#else
#define TARGET_IS_BIG_E NDIAN

No way or some way? TIA.

[Richard Tobin]

In article <27************ *************** *******@c19g200 0prf.googlegrou ps.com>,
perry.yuan <pe********@gma il.comwrote:

>How could I determine the endianness of my compile environment at
compile time, instead of run time?

You can't write a compile-time expression to determine it, because
endianness is a property of representations , not values, and there
are no objects whose representations can be examined at compile
time.

One solution is to run a program at compile time that determines
the endianness and outputs a suitable #define to a file which
you then include.

-- Richard
--
:wq

[Ben Pfaff]

"perry.yuan " <pe********@gma il.comwrites:

How could I determine the endianness of my compile environment at
compile time, instead of run time? I need a macro ("some_expressi on")

One way this is commonly done is to build in two stages. First,
compile and run a test program that tests for the
implementation' s endianness. Then use the test program's output
to configure macros to be defined while building the rest of the
program.
--
"I've been on the wagon now for more than a decade. Not a single goto
in all that time. I just don't need them any more. I don't even use
break or continue now, except on social occasions of course. And I
don't get carried away." --Richard Heathfield

[Eric Sosman]

perry.yuan wrote:

How could I determine the endianness of my compile environment at
compile time, instead of run time? I need a macro ("some_expressi on"),
i.e.

#if some_expression
#define TARGET_IS_LITTL E_ENDIAN
#else
#define TARGET_IS_BIG_E NDIAN

No way or some way? TIA.

This is Question 10.16 in the comp.lang.c Frequently
Asked Questions (FAQ) list <http://www.c-faq.com/>. You've
been around this newsgroup long enough to have seen the
FAQ mentioned several dozens of times; shame on you for
not bothering to read it.

--
Er*********@sun .com

[jacob navia]

perry.yuan wrote:

How could I determine the endianness of my compile environment at
compile time, instead of run time? I need a macro ("some_expressi on"),
i.e.

#if some_expression
#define TARGET_IS_LITTL E_ENDIAN
#else
#define TARGET_IS_BIG_E NDIAN

No way or some way? TIA.

#include <stdio.h>
int main(void)
{
union {
char c;
int i;
} u;
u.i = 0;
u.c = 1;

if (u.i == 1)
printf("little endian\n");
else
printf("big endian\n");
}

This printsd "little endian" in the intel processor,
"big endian" in the power pc. I think it should work.

--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique
http://www.cs.virginia.edu/~lcc-win32

[jacob navia]

jacob navia wrote:

perry.yuan wrote:

>How could I determine the endianness of my compile environment at
compile time, instead of run time? I need a macro ("some_expressi on"),
i.e.

#if some_expression
#define TARGET_IS_LITTL E_ENDIAN
#else
#define TARGET_IS_BIG_E NDIAN

No way or some way? TIA.

#include <stdio.h>
int main(void)
{
union {
char c;
int i;
} u;
u.i = 0;
u.c = 1;

if (u.i == 1)
printf("little endian\n");
else
printf("big endian\n");
}

This printsd "little endian" in the intel processor,
"big endian" in the power pc. I think it should work.

Sorry, I missed the "preprocess or" part.
--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique
http://www.cs.virginia.edu/~lcc-win32

[Willem]

jacob wrote:
) perry.yuan wrote:
)How could I determine the endianness of my compile environment at
)compile time, instead of run time? I need a macro ("some_expressi on"),
^^^^^^^ ^^^

) int main(void)
) {
) union {
) char c;
) int i;
) } u;
) u.i = 0;
) u.c = 1;
)
) if (u.i == 1)
) printf("little endian\n");
) else
) printf("big endian\n");
) }

Isn't that a run time solution ?
SaSW, Willem
--
Disclaimer: I am in no way responsible for any of the statements
made in the above text. For all I know I might be
drugged or something..
No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT

[Ben Pfaff]

jacob navia <ja***@nospam.c omwrites:

perry.yuan wrote:

>How could I determine the endianness of my compile environment at
compile time, instead of run time? I need a macro ("some_expressi on"),

This printsd "little endian" in the intel processor,
"big endian" in the power pc. I think it should work.

I don't think you actually read the OP's question.
--
Ben Pfaff
http://benpfaff.org

[Richard Tobin]

In article <sl************ ********@snail. stack.nl>,
Willem <wi****@stack.n lwrote:

>) int main(void)
) {
) union {
) char c;
) int i;
) } u;
) u.i = 0;
) u.c = 1;
)
) if (u.i == 1)
) printf("little endian\n");
) else
) printf("big endian\n");
) }

>Isn't that a run time solution ?

Not if you run it at compile time :-)

-- Richard
--
:wq

[jacob navia]

Richard Tobin wrote:

In article <sl************ ********@snail. stack.nl>,
Willem <wi****@stack.n lwrote:

>) int main(void)
) {
) union {
) char c;
) int i;
) } u;
) u.i = 0;
) u.c = 1;
)
) if (u.i == 1)
) printf("little endian\n");
) else
) printf("big endian\n");
) }

>Isn't that a run time solution ?

Not if you run it at compile time :-)

-- Richard

I sent a message recognizing my error around 30 seconds
after I sent the first answer.

Again:

Excuse, it was a mistake
--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique
http://www.cs.virginia.edu/~lcc-win32