_Complex常量 [英] _Complex constant
问题描述
有没有办法创建一个double _Complex类型的常量而没有
包括< complex.h>？
为什么_Complex_I是一个宏不是实现定义的常量？
谢谢。
a +，ld。
Laurent Deniau写道：
有没有办法在没有
的情况下创建double _Complex类型的常量< complex.h> ;?
>来自C99理由：
"我指定的后缀虚数常量不是必需的，因为
乘以I提供了一个足够方便且更多的
通常用于虚数术语的符号。
因此，除非你计算特定于实现的扩展，或者虚数部分为0的复杂的
常量，否则可能不是。
为什么_Complex_I是宏而不是实现定义的常量？
常量不能用于常量表达式。
#include< complex.h>
const double complex i = I; / *或等价，_Complex_I * /
复数复数v = 1 + 2 * i; / *错误：初始化元素不是
常数* /
Harald van D？3k写道：
< blockquote class =post_quotes>
Laurent Deniau写道：
>>有没有办法在没有包括< complex.h>？
>>来自C99理由：
" ;不需要用于指定虚构常量的I后缀，因为
乘以I提供了一个足够方便且更多的b $ b通常用于虚构术语的符号。
因此，除非你计算特定于实现的扩展，或复数
常数，假想部分为零，否则可能不是。
>>为什么_Complex_I是宏而不是实现定义的常量？
常量不能用于常量表达式。
#include< complex.h> ;
const double complex i = I; / *或等价，_Complex_I * /
复数复数v = 1 + 2 * i; / *错误：初始化元素不是
常数* /
对。通过指定''实现定义的常量''，我想是一个特殊的常量，如空指针常量。像__builtin_Complex_I那样将某些东西扩展到编译器常量。
我的问题是即使包含complex.h，gcc（4.1.2）在c99迂腐模式下给出一个
警告代码：
const double complex i = _Complex_I;
警告：虚构常量是GCC扩展
在complex.h中我们发现（如你所说）：
#define _Complex_I（__extension__ 1.0iF）
看来这个警告不合适，但gcc无法用这个定义知道
。任何线索？
谢谢。
a +，ld。
< blockquote> Laurent Deniau写道：
Harald van D？3k写道：
Laurent Deniau写道：
>为什么_Complex_I是宏而不是实现定义的常量？
常量不能用于常量表达式。
对。通过指定''实现定义的常量''，我想是一个特殊的常量，如空指针常量。例如，将
扩展为编译器常量的东西，例如__builtin_Complex_I。
嗯，这基本上是_Complex_I必须要做的。 （不是
标准明确，但我无法想象实现
会如何支持它。）如下所示，GCC使用编译器
常数本身。
我的问题是即使包含complex.h，gcc（4.1.2）给出了
$ b c99迂腐模式中的$ b警告代码：
const double complex i = _Complex_I;
警告：虚构常量是GCC扩展名
in complex.h我们发现（如你所说）：
#define _Complex_I（__extension__ 1.0iF）
看来这个警告不合适，但gcc无法用这个定义知道
。任何线索？
这是海湾合作委员会长期存在的错误：
http://gcc.gnu.org/PR7263
除了忽略警告之外别无他法，或使用
不同的编译器。
Is there any way to create a constant of type double _Complex without
including <complex.h>?
Why _Complex_I is a macro an not an implementation-defined constant?
Thanks.
a+, ld.
Laurent Deniau wrote:Is there any way to create a constant of type double _Complex without
including <complex.h>?
>From the C99 rationale:"An I suffix to designate imaginary constants is not required, as
multiplication by I provides a sufficiently convenient and more
generally useful notation for imaginary terms."
So unless you count implementation-specific extensions, or complex
constants with an imaginary part of zero, then no, probably not.
Why _Complex_I is a macro an not an implementation-defined constant?Constants can''t be used in constant expressions.
#include <complex.h>
const double complex i = I; /* or equivalently, _Complex_I */
double complex v = 1 + 2 * i; /* error: initializer element is not
constant */
Harald van D?3k wrote:Laurent Deniau wrote:
>>Is there any way to create a constant of type double _Complex without
including <complex.h>?
>>From the C99 rationale:"An I suffix to designate imaginary constants is not required, as
multiplication by I provides a sufficiently convenient and more
generally useful notation for imaginary terms."
So unless you count implementation-specific extensions, or complex
constants with an imaginary part of zero, then no, probably not.
>>Why _Complex_I is a macro an not an implementation-defined constant?
Constants can''t be used in constant expressions.
#include <complex.h>
const double complex i = I; /* or equivalently, _Complex_I */
double complex v = 1 + 2 * i; /* error: initializer element is not
constant */Right. By specifying ''implementation-defined constant'' I was thinking to
a special constant like null pointer constant. Something that would
expand to a compiler constant like __builtin_Complex_I for example.
My problem is that even with complex.h included, gcc (4.1.2) gives a
warning in c99 pedantic mode for the code:
const double complex i = _Complex_I;
warning: imaginary constants are a GCC extension
in complex.h we find (as you mention it):
#define _Complex_I (__extension__ 1.0iF)
It seems that this warning is not appropriate, but gcc cannot know with
this definition. Any clue?
Thanks.
a+, ld.
Laurent Deniau wrote:Harald van D?3k wrote:Laurent Deniau wrote:>Why _Complex_I is a macro an not an implementation-defined constant?Constants can''t be used in constant expressions.
Right. By specifying ''implementation-defined constant'' I was thinking to
a special constant like null pointer constant. Something that would
expand to a compiler constant like __builtin_Complex_I for example.Well, that''s basically what _Complex_I is required to do already. (Not
explicitly by the standard, but I can''t imagine how an implementation
would support it otherwise.) As you show below, GCC uses a compiler
constant itself.
My problem is that even with complex.h included, gcc (4.1.2) gives a
warning in c99 pedantic mode for the code:
const double complex i = _Complex_I;
warning: imaginary constants are a GCC extension
in complex.h we find (as you mention it):
#define _Complex_I (__extension__ 1.0iF)
It seems that this warning is not appropriate, but gcc cannot know with
this definition. Any clue?That''s a long-standing bug in GCC:
http://gcc.gnu.org/PR7263
There''s not much else to do but either ignore the warning, or use a
different compiler.
这篇关于_Complex常量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！
