将空指针解释为空（空字符串） [英] interpreting a null pointer as an empty (null string)
问题描述
哪个C库（当前和历史）将空指针解释为
a指向null（即空）字符串的指针？
Dennis Allison写道：
哪个C库（当前和历史）将空指针解释为
指向null（即空）字符串的指针？
至少有一个实现（前C-89），其中
花了很大的力气将0x0放在零位置
的数据段中。
因此，NULL指针（在该实现上为零）
总是指向一个位置，内容为''\0''
表示char *，其他指针的所有零位表示
那个位置。
毋庸置疑，当
代码被移植到另一个实现时，事情以无数方式爆发。
-
？
这是重要的可以做任何万无一失的事，因为傻瓜是这样的b $ b巧妙。 - A. Bloch
2004年3月5日星期五19:13:35 GMT，Nick Landsberg< hu ***** @ NOSPAM.att .net>
写道：
Dennis Allison写道：
其中C库（当前和历史）将空指针解释为指向null（即空）字符串的指针？
至少有一个实现（前C） -89），在数据段中将0x0放在零位置时非常痛苦。
因此，NULL指针（在该实现上为零）
总是指向一个内容为''\0''
的位置为char *，其他指针的所有零位为
该位置。
不用可以说，当代码被移植到另一个实现时，事情以无数种方式破裂。
甚至/那个/更接近于平台试图最小化
底池在C程序（用户代码或lib函数）的情况下的实际损坏
错误地将空指针视为指向
某事的有效指针。 />
我感觉到OP正在询问是否有任何字符串处理
库总是在交给char时检查特殊情况为0 *，
并在这种情况下做一些合理的事情。
我不知道，但是如果有那么那就必须考虑一些
一种非标准的扩展，它甚至可能会冒犯人们使用字符串lib函数来回答
，因为它意味着额外的特殊情况
开销正确使用这些指针会使其变得不必要。
无论如何，作为尼克的言论的后记，我被迫发出荣誉
给早期的MSVC团队建立我认为非常好的
小hack在调试模式下的运行时系统中：它们在零位置放置一个神奇的
值，并在程序执行后检查它是否已更改
。如果是这样，一个很好的诊断（NULL指针赋值...）是
发出的。这可能为我节省了无数个小时的头脑刮擦......
-leor
Leor Zolman
BD软件
le**@bdsoft.com
www.bdsoft.com - 使用C / C ++，Java，Perl& Sons进行现场培训。 Unix
C ++用户：下载BD Software的免费STL错误消息
Decryptor at www.bdsoft.com/tools/stlfilt.html
Leor Zolman< le * *@bdsoft.com>写道：
无论如何，作为尼克的言论的后记，我被迫向早期的MSVC团队表示赞赏，以确定我认为的是一个很好的小黑客在调试模式下的运行时系统中：它们在零位置放置一个神奇的值，并在程序执行后检查它是否已经改变。如果是，则发出良好的诊断（NULL指针分配...）。这可能为我节省了无数个小时的工作时间崩溃......
这比MSVC历史悠久。它绝对是在
甚至相当早期版本的Turbo C for DOS，而且我不记得
记得他们发明了这个想法的任何说法。
-
为了充分利用这本书，我强烈建议你阅读它。
- 理查德希思菲尔德
Which C libraries (current and historical) interpret a null pointer as
a pointer to a null (that is, empty) string?
Dennis Allison wrote:
Which C libraries (current and historical) interpret a null pointer as
a pointer to a null (that is, empty) string?
There was at least one implementation (pre C-89), which
took great pains into putting 0x0 at location zero
in the data segment.
Thus, the NULL pointer (on that implemenation a zero)
would always point to a location with the contents ''\0''
for a char *, and all zero bits for other pointers to
that location.
Needless to say, things broke in myriad ways when
code was ported to another implementation.
--
?
"It is impossible to make anything foolproof because fools are so
ingenious" - A. Bloch
On Fri, 05 Mar 2004 19:13:35 GMT, Nick Landsberg <hu*****@NOSPAM.att.net>
wrote:
Dennis Allison wrote:Which C libraries (current and historical) interpret a null pointer as
a pointer to a null (that is, empty) string?
There was at least one implementation (pre C-89), which
took great pains into putting 0x0 at location zero
in the data segment.
Thus, the NULL pointer (on that implemenation a zero)
would always point to a location with the contents ''\0''
for a char *, and all zero bits for other pointers to
that location.
Needless to say, things broke in myriad ways when
code was ported to another implementation.
And even /that/ is more to the tune of "the platform tries to minimize the
potential damage in the case when a C program (user code or lib function)
mistakenly treats a null pointer as if it were a valid pointer to
something".
I get the feeling the OP was asking if there are/were any string-handling
libraries that always check for a special-case of 0 when handed a char *,
and do some reasonable thing in that case.
I don''t know, but if there were then that would have to be considered some
sort of non-standard extension, and it might even be offensive to folks
using the string lib functions because it implies extra special-case
overhead that proper use of those pointers would have rendered unnecessary.
Anyway, as a postscript to Nick''s remarks, I''m compelled to give out kudos
to the early MSVC team for establishing what I think was an excellent
little "hack" in their runtime system in debug mode: They place a magic
value at location zero, and after program execution check to see if it has
changed. If so, a nice diagnostic ("NULL pointer assignment...") is
emitted. This has probably saved me countless hours of head-scratching over
runtime meltdowns...
-leor
Leor Zolman
BD Software
le**@bdsoft.com
www.bdsoft.com -- On-Site Training in C/C++, Java, Perl & Unix
C++ users: Download BD Software''s free STL Error Message
Decryptor at www.bdsoft.com/tools/stlfilt.html
Leor Zolman <le**@bdsoft.com> writes:
Anyway, as a postscript to Nick''s remarks, I''m compelled to give out kudos
to the early MSVC team for establishing what I think was an excellent
little "hack" in their runtime system in debug mode: They place a magic
value at location zero, and after program execution check to see if it has
changed. If so, a nice diagnostic ("NULL pointer assignment...") is
emitted. This has probably saved me countless hours of head-scratching over
runtime meltdowns...
This has a much older history than MSVC. It was definitely in
even fairly early versions of Turbo C for DOS, and I don''t
remember any claims that they invented the idea.
--
"To get the best out of this book, I strongly recommend that you read it."
--Richard Heathfield
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