NULL指针和零值 [英] NULL pointer and zero value
问题描述
如果我有一个指针char * p，通过以下方式为此
指针指定NULL是否正确：
" memset（& p ，0，sizeof（p））;而不是p = NULL;
我问的原因是我有一个N函数结构数组
变量，例如，
typedef struct
{
int（* func1）（）;
int（* func2 ）（）;
void *（* func2）（int）;
} ModuleFunctions;
#define N 100
ModuleFunction garMF [N];
初始化时，不要为每个
函数成员构造一个循环来分配NULL对于每个数组成员的ModuleFunction，是
它是正确的，例如
memset（garMF，0，sizeof（ModuleFunctions）* N）;
感谢您的帮助，
DT
If I have a pointer char * p, is it correct to assign NULL to this
pointer by:
"memset( &p, 0, sizeof(p));" instead of "p = NULL;"
The reason I ask is I have an array of structure of N function
variables, for example,
typedef struct
{
int (* func1)();
int (* func2)();
void * (* func2)(int );
} ModuleFunctions;
#define N 100
ModuleFunction garMF[N];
When initializing, instead of making a loop to assgin NULL to each
function member of struct ModuleFunction for each member of array, is
it correct to do something like
memset( garMF, 0, sizeof(ModuleFunctions)*N );
Thanks for your help,
DT
推荐答案
vp写道：
vp wrote:
如果我有一个指针char * p，通过以下方式为这个
指针指定NULL是否正确：
" memset（& p， 0，sizeof（p））;而不是p = NULL;
If I have a pointer char * p, is it correct to assign NULL to this
pointer by:
"memset( &p, 0, sizeof(p));" instead of "p = NULL;"
编号NULL不一定是全位零。
但是，你的技术会在很多平台上偶然发挥作用，因为很多平台都会使用all-bits-zero来表示NULL。如果你喜欢
编程一个赌场，请继续。 :-)
< snip>
-
Richard Heathfield： bi **** @ eton.powernet.co.uk
Usenet是一个奇怪的地方。 ; - Dennis M Ritchie，1999年7月29日。
C FAQ： http://www.eskimo.com/~scs/C-faq/top.html
K& R答案，C书等：< a rel =nofollowhref =http://users.powernet.co.uk/etontarget =_ blank> http://users.powernet.co.uk/eton
No. NULL is not necessarily all-bits-zero.
Your technique will, however, work by chance on quite a few platforms,
because quite a few platforms do use all-bits-zero for NULL. If you like
programming-by-casino, go ahead. :-)
<snip>
--
Richard Heathfield : bi****@eton.powernet.co.uk
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton
Richard Heathfield< in ***** @ address.co.uk.invalid>这样说：
Richard Heathfield <in*****@address.co.uk.invalid> spoke thus:
（所有位0为空的帖子）
(all-bits 0 as NULL post)
如果你喜欢按赌场编程，请去先。 ： - ）
If you like programming-by-casino, go ahead. :-)
所以房子赢得NULL和双NULL？ ;）
-
Christopher Benson-Manica |我*应该*知道我在说什么 - 如果我
ataru（at）cyberspace.org |不，我需要知道。火焰欢迎。
So the house wins on NULL and double NULL? ;)
--
Christopher Benson-Manica | I *should* know what I''m talking about - if I
ataru(at)cyberspace.org | don''t, I need to know. Flames welcome.
dt ******* @ yahoo。 com （vp）写道：
dt*******@yahoo.com (vp) writes:
如果我有一个指针char * p，通过以下方式为此指针指定NULL是否正确：
" memset（& p，0，sizeof（p））;"而不是p = NULL;
编号前一个语句将'p''的所有位设置为零，这不是
必然是空指针的表示。
我问的原因是我有一个N函数
变量的结构数组，例如，
typedef struct
{
int（* func1）（）;
int（* func2）（）;
void *（* func2）（int）;
} ModuleFunctions;
#define N 100
ModuleFunction garMF [N];
初始化时，不是为每个数组成员的struct ModuleFunction的每个
函数成员设置一个循环，而是
正确做一些像memset（garMF，0，sizeof（ModuleFunctions）* N）;
If I have a pointer char * p, is it correct to assign NULL to this
pointer by:
"memset( &p, 0, sizeof(p));" instead of "p = NULL;"
No. The former statement sets all bits of `p'' to zero, which is not
necessarily a representation of the null pointer.
The reason I ask is I have an array of structure of N function
variables, for example,
typedef struct
{
int (* func1)();
int (* func2)();
void * (* func2)(int );
} ModuleFunctions;
#define N 100
ModuleFunction garMF[N];
When initializing, instead of making a loop to assgin NULL to each
function member of struct ModuleFunction for each member of array, is
it correct to do something like
memset( garMF, 0, sizeof(ModuleFunctions)*N );
如果`garMF''有静态存储持续时间，如果你没有明确地初始化它，它会自动初始化为
零。 初始化为零意味着每个非复合对象被初始化，就好像你给它分配了'0''/ b $ b（即指针被初始化为空指针）。对于复合对象，
其成员或元素以这种方式递归初始化。
否则（如果`garMF''没有静态存储持续时间）你将循环使用
。
马丁
If `garMF'' has static storage duration, it is automatically initialized to
zero if you don''t initialize it explicitly. "Initialized to zero" means
that each non-compound object is initialized as if you assigned `0'' to it
(i.e. pointers are initialized to null pointers). For compound objects,
its members or elements are recursively initialized in this way.
Otherwise (if `garMF'' doesn''t have static storage duration) you''ll have
to loop.
Martin
这篇关于NULL指针和零值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
