NULL与0 [英] NULL vs. 0
问题描述
我搜索了这个问题的常见问题解答，无法真正找到答案。
从风格上讲，使用0或NULL更好吗？
我知道预标准，0是推荐的，因为有些编译器
不正确地实现了NULL。
但是，18.1 / 4（脚注） 180）表示0和0L是有效的NULL，
而（void *）0明显无效。
因此，假设（合理）标准符合编译器，是否有一个
的理由继续优先于0而不是NULL？ NULL似乎具有
优势，表明我们正在检查一个指针。
另外，nullptr使它进入C ++ 0x草案？
I searched the FAQ on this one, couldn''t really find an answer.
Stylistically, is it better to use 0 or NULL?
I know that pre-Standard, 0 was recommended, because some compilers
implemented NULL improperly.
However, 18.1/4(footnote 180) indicates that 0 and 0L are valid NULLs,
while (void*)0 is explicitly invalid.
So, assuming a (reasonably) Standard compliant compiler, is there a
reason to continue to prefer 0 over NULL? NULL would seem to have the
advantage of indicating that we''re checking a pointer.
Also, did nullptr make it into the C++0x draft?
推荐答案
>来自The C ++ Language：
Zero（0）is一个int。由于标准转换，0可以用作任何积分，浮点，指针或指针成员
类型的
常量。零的类型将由上下文确定。零将
通常（但不总是）由全零的位模式表示
的适当大小。
无对象分配地址为0.因此，0充当
指针文字，表示指针没有引用
对象。
在C中，定义一个宏NULL代表一个零
指针很受欢迎。由于C ++的类型检查更严格，使用普通0，
而不是任何建议的NULL宏，可以减少问题。
red floyd写道：
>From "The C++ Language":
Zero (0) is an int. Because of standard conversions, 0 can be used as a
constant of any integral, floating-point, pointer, or pointer-to-member
type. The type of zero will be determined by context. Zero will
typically (but not always) be represented by a bit-pattern of all-zeros
of the appropriate size.
No object is allocated with the address of 0. Consequently, 0 acts as a
pointer literal, indicating that the pointer doesn''t refer to an
object.
In C, it has been popular to define a macro NULL to represent a zero
pointer. Because of C++''s tighter type checking, the use of plain 0,
rather than any suggested NULL macro, leads to fewer problems.
red floyd wrote:
我搜索了这个问题的常见问题解答，无法找到答案。
从风格上看，使用0还是NULL更好？
我知道pre-Standard，0是推荐的，因为有些编译器不正确地实现了NULL。
然而，18.1 / 4（脚注180）表明0和0L是有效的NULL，
while（void *）0显然无效。
因此，假设一个（合理的）符合标准的编译器，是否有理由继续优先于0而不是NULL？ NULL似乎具有指示我们正在检查指针的优点。
另外，nullptr是否使它进入C ++ 0x草案？
I searched the FAQ on this one, couldn''t really find an answer.
Stylistically, is it better to use 0 or NULL?
I know that pre-Standard, 0 was recommended, because some compilers
implemented NULL improperly.
However, 18.1/4(footnote 180) indicates that 0 and 0L are valid NULLs,
while (void*)0 is explicitly invalid.
So, assuming a (reasonably) Standard compliant compiler, is there a
reason to continue to prefer 0 over NULL? NULL would seem to have the
advantage of indicating that we''re checking a pointer.
Also, did nullptr make it into the C++0x draft?
ra****@gmail.com 写道：
ra****@gmail.com wrote:
red floyd写道：
red floyd wrote:
我搜索了这个问题的常见问题解答，无法找到答案。
风格，使用0或NULL更好吗？
我知道预标准，0推荐，因为有些编译器实现了NULL不正确。
但是， 18.1 / 4（脚注180）表示0和0L是有效的NULL，
而（void *）0明显无效。
因此，假设（合理的）符合标准的编译器，有理由继续优先于0而不是NULL吗？ NULL似乎具有指示我们正在检查指针的优点。
另外，nullptr是否使它进入C ++ 0x草案？
I searched the FAQ on this one, couldn''t really find an answer.
Stylistically, is it better to use 0 or NULL?
I know that pre-Standard, 0 was recommended, because some compilers
implemented NULL improperly.
However, 18.1/4(footnote 180) indicates that 0 and 0L are valid NULLs,
while (void*)0 is explicitly invalid.
So, assuming a (reasonably) Standard compliant compiler, is there a
reason to continue to prefer 0 over NULL? NULL would seem to have the
advantage of indicating that we''re checking a pointer.
Also, did nullptr make it into the C++0x draft?
FromThe C ++ Language：
From "The C++ Language":
零（0）是一个int。由于标准转换，0可用作任何整数，浮点，指针或指向成员的类型的常量。零的类型将由上下文确定。零通常（但不总是）由适当大小的全零的位模式表示。
没有分配地址为0的对象。因此，0表示作为
指针文字，表示指针没有引用
对象。
在C中，定义宏NULL表示零已经很流行了
指针。由于C ++的类型检查更严格，使用普通0，而不是任何建议的NULL宏，可以减少问题。
Zero (0) is an int. Because of standard conversions, 0 can be used as a
constant of any integral, floating-point, pointer, or pointer-to-member
type. The type of zero will be determined by context. Zero will
typically (but not always) be represented by a bit-pattern of all-zeros
of the appropriate size.
No object is allocated with the address of 0. Consequently, 0 acts as a
pointer literal, indicating that the pointer doesn''t refer to an
object.
In C, it has been popular to define a macro NULL to represent a zero
pointer. Because of C++''s tighter type checking, the use of plain 0,
rather than any suggested NULL macro, leads to fewer problems.
1.请不要'' t top post
（ http://www.parashift.com/c++-faq-lit....html#faq-5.4) 。
重新排列以符合cl c ++网络礼仪。
2.我有，并且已经阅读了TC ++ PL3e。我的观点是因为
标准18.1 / 4在本国际标准（4.10）中指定宏NULL是实现定义的
空指针常量。脚注
180到18.1 / 4特别禁止（void *）0，是否有任何好的现代
理由再使用0而不是NULL？
1. Please don''t top post
(http://www.parashift.com/c++-faq-lit....html#faq-5.4).
Rearranged to conform to c.l.c++ netiquette.
2. I have, and have read TC++PL3e. My point was that because the
Standard 18.1/4 specifies "The macro NULL is an implementation-defined
null pointer constant in this International Standard (4.10)." Footnote
180 to 18.1/4 specifically disallows (void*)0, is there any good modern
reason to use 0 instead of NULL anymore?
red floyd写道：
red floyd wrote:
...
因此，假设一个（合理的）符合标准的编译器，是否有理由继续偏好0而不是NULL？ NULL似乎具有指示我们正在检查指针的优点。
...
...
So, assuming a (reasonably) Standard compliant compiler, is there a
reason to continue to prefer 0 over NULL? NULL would seem to have the
advantage of indicating that we''re checking a pointer.
...
因为这个原因它在指针上下文中更喜欢NULL超过0。
否则，它们是等价的（在这种情况下）。
-
祝你好运，
Andrey Tarasevich
For that very reason it makes sense to prefer NULL over 0 in pointer context.
Otherwise, they are equivalent (in such contexts).
--
Best regards,
Andrey Tarasevich
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