_复杂的long int [英] _Complex long int
问题描述
tl; dr;
Q int 在中是什么意思_Complex long int ？为什么它是 legal？
更长版本
将某些32位代码移植为64位安全。
在一个地方，我注意到它使用了
静态__complex__ long int i32X [256];
笨拙的搜索并替换为int32_t的 long int更改给了我一个编译错误。
__complex__是较老的GNUism，已由标准_Complex取代。
以下是重现该问题的简短代码段：
#include< complex.h>
#include< inttypes.h>
typedef _Complex long int WhyAmILegal;
typedef _Complex int32_t Snafu;
typedef int32_t _Complex Snafu2;
在gcc下编译得到：
complextest.c：6：26：错误：在'Snafu'之前应为'='，'，'，';'，'asm'或'__attribute__'
typedef _Complex int32_t Snafu ;
^ ~~~~
complextest.c：8：17：错误：声明说明符中的两个或多个数据类型
typedef int32_t _Complex Snafu2;
（草稿） C11标准说：
有三种复杂类型，分别指定为float _Complex，double
_Complex和long double _Complex.43）（复杂类型是实现不需要支持的有条件
功能；请参见6.10.8.3。）
因此，这里的错误似乎是当仅浮点复杂类型合法时，我试图请求一个整数复杂类型。
_Complex long 的含义实际上更像是 _Complex long double 。
我认为这可能是gcc解析器中的错误
_Complex long int
也可以在在线铛下正常编译。 / p>
那么为什么 int 在这里合法。
感谢@ Keith-Thompson's指出整数复数是GNU扩展，是clang支持的扩展。
另一个数据点。以下程序：
#include< complex.h>
#include< inttypes.h>
#include< stdio.h>
typedef _Complex long int ComplexLong;
typedef _Complex short int ComplexShort;
typedef _Complex int ComplexInt;
int main（void）
{
fprintf（stderr， sizeof（_Complex long int）=％d\n，sizeof（ComplexLong））;
fprintf（stderr， sizeof（_Complex int）=％d\n，sizeof（ComplexInt））;
fprintf（stderr， sizeof（_Complex short int）=％d\n，sizeof（ComplexShort））;
fprintf（stderr， sizeof（short int）=％d\n，sizeof（short int））;
fprintf（stderr， sizeof（int）=％d\n，sizeof（int））;
fprintf（stderr， sizeof（long int）=％d\n，sizeof（long int））;
返回0；
}
使用以下方式编译：
all：complextest complextest32
complextest：complextest.c
$（CC）-o $ @ $<
complextest32：complextest.c
$（CC）-m32 -o $ @ $<
（使用gcc编译）并运行时：
> ./ complextest
sizeof（_Complex long int）= 16
sizeof（_Complex int）= 8
sizeof（_Complex short int ）= 4
sizeof（short int）= 2
sizeof（int）= 4
sizeof（long int）= 8
> ./ complextest32
sizeof（ _Complex long int）= 8
sizeof（_Complex int）= 8
sizeof（_Complex short int）= 4
sizeof（short int）= 2
sizeof（int）= 4
sizeof（long int）= 4
所以 _Complex long int像不能以体系结构不变的方式指定。您应该使用 long 这样的 _Complex int 或 _Complex short 来提高可移植性。
这是一个gcc扩展，如您所见，通过（或多或少）遵循C模式进行编译：
$ cat cc
_Complex double cd;
_Complex long int cli;
$ gcc -c cc
$ gcc -c -std = c11 -pedantic cc
cc：2：1：警告：ISO C不支持复杂的整数类型[-Wpedantic]
_Complex long int cli;
^ ~~~~~~~
$
这是记录在gcc手册中：
ISO C99支持复杂的浮动数据类型，并且作为扩展GCC
在C90模式和C ++中支持它们。 GCC还支持不属于ISO C99的复杂
整数数据类型。
clang并不奇怪，支持相同的
要回答添加的问题， _Complex 是类型说明符。 _Complex int32_t 无效，原因与 unsigned int32_t 无效相同。类型说明符不能应用于typedef。
tl;dr;
Q what does int mean in _Complex long int? Why is it legal?
Longer version
I was porting some 32-bit code to be 64-bit safe. In one place I noted it uses:
static __complex__ long int i32X[256];
A dumb search and replace changing "long int" for int32_t gave me a compilation error. __complex__ is an older GNUism which has been replaced by the standard _Complex. Here is a short code snippet to reproduce the issue:
#include <complex.h>
#include <inttypes.h>
typedef _Complex long int WhyAmILegal;
typedef _Complex int32_t Snafu;
typedef int32_t _Complex Snafu2;
Compiled under gcc gives:
complextest.c:6:26: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘Snafu’
typedef _Complex int32_t Snafu;
^~~~~
complextest.c:8:17: error: two or more data types in declaration specifiers
typedef int32_t _Complex Snafu2;
The (draft) C11 standard says:
"There are three complex types, designated as float _Complex, double _Complex, and long double _Complex.43) (Complex types are a conditional feature that implementations need not support; see 6.10.8.3.) The real floating and complex types are collectively called the floating types."
So the bug here would seem to be that I am trying to request an integral complex type when only floating point complex types are legal.
The meaning of _Complex long is actually more like _Complex long double.
I thought it might be a bug in gcc's parser, however
_Complex long int
compiles just fine under clang online as well.
So why is int 'legal' here.
Thanks to @Keith-Thompson's for pointing out that integral complex numbers are a GNU extension and one that is supported by clang.
Another data point. The following program:
#include <complex.h>
#include <inttypes.h>
#include <stdio.h>
typedef _Complex long int ComplexLong;
typedef _Complex short int ComplexShort;
typedef _Complex int ComplexInt;
int main(void)
{
fprintf(stderr,"sizeof(_Complex long int)=%d\n",sizeof(ComplexLong));
fprintf(stderr,"sizeof(_Complex int)=%d\n",sizeof(ComplexInt));
fprintf(stderr,"sizeof(_Complex short int)=%d\n",sizeof(ComplexShort));
fprintf(stderr,"sizeof(short int)=%d\n",sizeof(short int));
fprintf(stderr,"sizeof(int)=%d\n",sizeof(int));
fprintf(stderr,"sizeof(long int)=%d\n",sizeof(long int));
return 0;
}
Compiled using:
all: complextest complextest32
complextest: complextest.c
$(CC) -o$@ $<
complextest32: complextest.c
$(CC) -m32 -o$@ $<
when (compiled using gcc) and run gives:
>./complextest
sizeof(_Complex long int)=16
sizeof(_Complex int)=8
sizeof(_Complex short int)=4
sizeof(short int)=2
sizeof(int)=4
sizeof(long int)=8
>./complextest32
sizeof(_Complex long int)=8
sizeof(_Complex int)=8
sizeof(_Complex short int)=4
sizeof(short int)=2
sizeof(int)=4
sizeof(long int)=4
So _Complex long int like long cannot be specified in an architecture invariant manner. You should use _Complex int or _Complex short to be slightly more portable.
It's a gcc extension, as you can see by compiling in (more or less) conforming C mode:
$ cat c.c
_Complex double cd;
_Complex long int cli;
$ gcc -c c.c
$ gcc -c -std=c11 -pedantic c.c
c.c:2:1: warning: ISO C does not support complex integer types [-Wpedantic]
_Complex long int cli;
^~~~~~~~
$
This is documented in the gcc manual:
ISO C99 supports complex floating data types, and as an extension GCC supports them in C90 mode and in C++. GCC also supports complex integer data types which are not part of ISO C99.
clang, not surprisingly, supports the same extension.
To answer the added question, _Complex is a type specifier. _Complex int32_t is invalid for the same reason unsigned int32_t is invalid. Type specifiers can't be applied to typedefs.
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