问题描述
您好，
null和NULL之间有什么区别。是x == null和x ==
NULL是一样的吗？编译器是gcc 3.2。
谢谢。
Hello,
What is the difference between null and NULL. Are x == null and x ==
NULL the same? The compiler is gcc 3.2.
Thanks.
推荐答案
NULL被你的实现定义为空指针常量。
null不需要定义标准在一个实现中。
见clc-faq第5节
问候
Irrwahn
-
伟大的思想在大圈子里奔跑。
NULL is defined as a null pointer constant by your implementation.
null isn''t required by the standard to be defined in an implementation.
See c.l.c-faq section 5
http://www.eskimo.com/~scs/C-faq/top.html
Regards
Irrwahn
--
Great minds run in great circles.
NULL被你的实现定义为空指针常量。
null不需要定义标准在一个实现中。
见clc-faq第5节
问候
Irrwahn
-
伟大的思想在大圈子里奔跑。
NULL is defined as a null pointer constant by your implementation.
null isn''t required by the standard to be defined in an implementation.
See c.l.c-faq section 5
http://www.eskimo.com/~scs/C-faq/top.html
Regards
Irrwahn
--
Great minds run in great circles.
C语言有NULL但没有null。写作时我使用NULL来表示在< stdlib.h>中定义的宏。并在讨论指针时。我讨论null字符时
使用null。通过null字符我是
指的是''\'''。
如果你要求区别的那么语义
介于（x ==''\'''）和（x == NULL）之间，它取决于x是什么。关闭
顶部，他们将评估所有x的相同结果。我，
亲自使用（x ==''\'''）如果x是char或int而且（x == NULL）如果x是
a指针。对于其他一切，您必须考虑
比较是否有效以及如何转换或推广。
-
darrell at cs dot toronto dot edu
或
main（）{int j = 1234; char t [] ="：@ abcdefghijklmnopqrstuvwxyz.\ n"，* i =
" iqgbgxmdbjlgdv.lksrqek.n" ;; char * strchr（const char *，int）; while（
* i）{j + = strchr（t，* i ++） - t; j％= sizeof t-1; putchar（t [j]）;} return 0;}
C language has a NULL but there is no null. When writing I use NULL to
indicate the macro defined in <stdlib.h> and when discussing pointers. I
use null when discussing the null character. By null character I am
referring to ''\0''.
With that semantics out of the way, if you are asking for the difference
between (x == ''\0'') and (x == NULL) it would depend on what x is. Off the
top of my head, they will evaluate to the same result for all x. I,
personally, use (x == ''\0'') if x is a char or int and (x == NULL) if x is
a pointer. For everything else you''d have to consider whether the
comparison is valid and how things will be converted or promoted.
--
darrell at cs dot toronto dot edu
or
main(){int j=1234;char t[]=":@abcdefghijklmnopqrstuvwxyz.\n",*i=
"iqgbgxmdbjlgdv.lksrqek.n";char *strchr(const char *,int);while(
*i){j+=strchr(t,*i++)-t;j%=sizeof t-1;putchar(t[j]);} return 0;}
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