标准变化 [英] standard change
问题描述
标准必须有一些变化，因为我遇到了这个错误
我把这行放在标题中。
#pragma once
我只希望标题包含一次。编译器说了一些关于过时的事情
。
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*这样说起Bill Cunningham< no **** @ nspam.net>：
你好，
我只想把标题包含一次。
使用？include后卫？它们是标准的，＃pragma曾经不是。
Wolfgang。
-
" Erfahrungen - das sind die vernarbten Wunden unserer Dummheit 。
- John Osborne
" Bill Cunningham" <无**** @ nspam.net>写道：
标准中必须有一些变化，因为当我把这一行放在标题中时我遇到了这个错误。
#pragma once
我只希望将标题包含一次。编译器说过了一些关于过时的东西。
编译指示的行为是实现定义的（除了少数例外情况
C99中的
） ，但是`#pragma once''不是其中之一）。因此，编译器
实现者可以在不违反标准的情况下更改或弃用某些pragma
的含义。
< OT> ;
如果有问题的编译器是GCC C编译器：尽管在当前版本中标记为过时的
，`#pragma once''将继续
适用于未来版本。
引自< http://gcc.gnu.org/gcc-3.4/changes.html>：
|预处理器中的文件处理已被重写。海湾合作委员会不再
|通过符号链接和硬链接感到困惑，现在有一个正确的
|执行#import和#pragma一次。这两个指令有
|所以一直没有弃用。
< / OT>
<更多OT>
难道不应该反义词弃用是预先的而不是
取消弃用？ ;）
< /更多OT>
Martin
Bill Cunningham写道：< blockquote class =post_quotes>标准中必须有一些变化因为我把这行放在标题中时遇到了这个错误。
#pragma once
我只想要标题被包括一次。编译器说了一些关于过时的东西。
直到C99，没有特定的#pragma具有标准定义的含义。
使用新标准，我们有一些#pragmas，意思是希望
具有超过特定于实现的含义。这些包括
#pragma STDC FP_CONTRACT开关开关
#pragma STDC FENV_ACCESS开关开关
#pragma STDC CX_LIMITED_RANGE on-关闭开关
其中开关是ON，OFF和DEFAULT之一
这9种形式可能已由其他我不知道的形式补充，但是
#pragma一次
已经_never_标准。由于系统头至少是从C99，
幂等，并且使用普通防护装置可以有效地制作头部，
不需要''#pragma一次正如你所描述的那样。
-
Martin Ambuhl
There must be some change in the standard because I ran into this error when
I put this line in a header.
# pragma once
I only wanted the headers to be included once. The compiler said something
about obsolete.
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* Thus spoke Bill Cunningham <no****@nspam.net>:
Hallo,
I only wanted the headers to be included once.
Use ?include guards?. They are standard, #pragma once is not.
Wolfgang.
--
"Erfahrungen -- das sind die vernarbten Wunden unserer Dummheit."
-- John Osborne
"Bill Cunningham" <no****@nspam.net> writes:
There must be some change in the standard because I ran into this
error when I put this line in a header.
# pragma once
I only wanted the headers to be included once. The compiler said
something about obsolete.
The behavior of pragmas is implementation-defined (with a few exceptions
in C99, but `#pragma once'' is not one of them). Therefore, the compiler
implementor can change the meaning of or deprecate certain pragmas
without violating the standard.
<OT>
In case the compiler in question is the GCC C compiler: Despite being
marked obsolete in the current version, `#pragma once'' will continue to
work in future versions.
To quote from <http://gcc.gnu.org/gcc-3.4/changes.html>:
| File handling in the preprocessor has been rewritten. GCC no longer
| gets confused by symlinks and hardlinks, and now has a correct
| implementation of #import and #pragma once. These two directives have
| therefore been un-deprecated.
</OT>
<even more OT>
Shouldn''t the antonym of "deprecate" be "precate" instead of
"un-deprecate"? ;)
</even more OT>
Martin
Bill Cunningham wrote:There must be some change in the standard because I ran into this error when
I put this line in a header.
# pragma once
I only wanted the headers to be included once. The compiler said something
about obsolete.
Until C99, no particular #pragma had a meaning defined by the standard.
With the new standard, we have a handful of #pragmas with meanings hoped to
have more than implementation-specific meanings. These include
#pragma STDC FP_CONTRACT on-off-switch
#pragma STDC FENV_ACCESS on-off-switch
#pragma STDC CX_LIMITED_RANGE on-off-switch
where on-off-switch is one of ON, OFF, and DEFAULT
These 9 forms may have been supplemented by others that I don''t know, but
#pragma once
has _never_ been standard. Since system headers are, at least from C99,
idempotent, and with normal guards your headers can be made effectively so,
there is no need for ''#pragma once'' as you describe it.
--
Martin Ambuhl
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