Endian检查宏 [英] Endian check macro
问题描述
大家好，
我试着写一个宏来检查系统是大端还是小端
但没有成功。不要误会我的意思，我写一个函数没问题，或者说b $ ba一个班轮就可以做到这一点，但我试图在一个_macro_中做这个没有
副作用（无全局变量声明）。我怀疑这不是
可能。
有人在乎证明我错了吗？
-
Guillaume Dargaud
http://www.gdargaud.net/
Guillaume Dargaud写道：
大家好，
我试着编写一个宏来检查一个系统是大端还是一个小的
endian没有成功。不要误会我的意思，我没有问题写一下
a函数或者一个内衬来做那件事，但是我试图在一个
_macro_中做到这一点副作用（无全局变量声明）。我怀疑这是不可能的。
任何人都在乎证明我错了吗？
#include< stdio.h>
#define ENDIAN（）{\
volatile unsigned long ul = 1; \
volatile unsigned char * p; \
p =（volatile unsigned char *）& ul; \
if（* p == 1）\
puts（Little endian。）; \
else if（*（ p +（sizeof（unsigned long）-1））== 1）\
puts（Big endian。）; \
else puts（" ;未知的endian。"）; \
}
int main（无效）{
ENDIAN（）;
返回0;
}
" Guillaume Dargaud" < us ***************************** @ www.gdargaud.ne t>
写道：
我试着写一个宏来检查系统是大端还是小端
但没有成功。不要误会我的意思，我写一个函数没问题，或者说b $ ba一个班轮就可以做到这一点，但我试图在一个_macro_中做这个没有
副作用（无全局变量声明）。我怀疑这不是
可能。
有人在乎证明我错了吗？
在C99中你可以使用复合文字来获得类似效果
你想要的东西[1]：
（union {short n; char b [sizeof（short）];}）{。n = 1} .b [0]
Wrap，但是你想要它，在一个宏观中。 unsigned char可能更好用
一般而且这个代码有一千个问题，但没有
你正在做什么的一些细节，我不能建议更多< b / b
健壮。
[1]我对使用
机器测试endian-ness的代码持谨慎态度它不是两个普遍接受的
替代品。
-
Ben。
2008年7月8日11:35，santosh写道：
#define ENDIAN（）{\
volatile unsigned long ul = 1; \
volatile unsigned char * p; \
p =（volatile unsigned char *）& ul; \
if（* p == 1）\
puts（Little endian。）; \
else if（*（ p +（sizeof（unsigned long）-1））== 1）\
puts（Big endian。）; \
else puts（" ;未知的结尾。 "）; \
}
这是一个非常实用的解决方案，Santosh。我很惊讶没有人'
来警告你（volatile unsigned char *）& ul可能
包含陷阱表示并解除引用它导致UB，或者一些
这样的废话。
Hello all,
I tried to write a macro to check if a system is big endian or little endian
with no success. Don''t get me wrong, I have no problem writing a function or
a one liner to do that, but I was trying to do it in a _macro_ with no
side-effect (no global variable declaration). I suspect this is not
possible.
Anyone cares to prove me wrong ?
--
Guillaume Dargaud
http://www.gdargaud.net/
Guillaume Dargaud wrote:
Hello all,
I tried to write a macro to check if a system is big endian or little
endian with no success. Don''t get me wrong, I have no problem writing
a function or a one liner to do that, but I was trying to do it in a
_macro_ with no side-effect (no global variable declaration). I
suspect this is not possible.
Anyone cares to prove me wrong ?#include <stdio.h>
#define ENDIAN() { \
volatile unsigned long ul = 1;\
volatile unsigned char *p;\
p = (volatile unsigned char *)&ul;\
if (*p == 1)\
puts("Little endian.");\
else if (*(p+(sizeof(unsigned long)-1)) == 1)\
puts("Big endian.");\
else puts("Unknown endian.");\
}
int main(void) {
ENDIAN();
return 0;
}
"Guillaume Dargaud" <us*****************************@www.gdargaud.ne t>
writes:
I tried to write a macro to check if a system is big endian or little endian
with no success. Don''t get me wrong, I have no problem writing a function or
a one liner to do that, but I was trying to do it in a _macro_ with no
side-effect (no global variable declaration). I suspect this is not
possible.
Anyone cares to prove me wrong ?In C99 you can use a compound literal to get something like the effect
you want[1]:
(union {short n; char b[sizeof(short)];}){.n = 1}.b[0]
Wrap, however you want it, in a macro. unsigned char might better in
general and there are a thousand issues with this code but without
some details of what you are doing, I can''t suggest anything more
robust.
[1] I am wary of code that tests for endian-ness since I''ve used
machines where it is neither of the two commonly accepted
alternatives.
--
Ben.
On 8 Jul 2008 at 11:35, santosh wrote:#define ENDIAN() { \
volatile unsigned long ul = 1;\
volatile unsigned char *p;\
p = (volatile unsigned char *)&ul;\
if (*p == 1)\
puts("Little endian.");\
else if (*(p+(sizeof(unsigned long)-1)) == 1)\
puts("Big endian.");\
else puts("Unknown endian.");\
}That''s a remarkably practical solution, Santosh. I''m surprised no one''s
been along yet to warn you that (volatile unsigned char *)&ul might
contain a trap representation and dereferencing it cause UB, or some
such nonsense.
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