c ++和< complex.h>与< complex>在单独的文件

问题描述

注意：

我正在使用Apple LLVM版本6.0（clang-600.0.56）（基于LLVM 3.5svn）在OSX上进行编译

具体来说，我试图从LibIIR编译一个整体源，一个​​过滤库，维护

我已经看过这个答案了。关于同时使用

$ < complex.h>

设置：

我有一个文件 iir.h >

  #include< complex.h> 
 
 #ifdef __cplusplus 
 externC{
 #endif 
 
 ... 
  pre> 
 
 
我有C ++源文件和头文件 libiir ++。cpp 和 iir ++。h 如下：
  / *** libiir ++。cpp *** / 
我们需要首先包括iir.h，因为它拉入< complex.h> ;,其中我们需要
 //在iir ++。h拉入< complex> 
 #includeiir.h
 
 //现在删除复杂的预处理器定义到_Complex，这是罚款
 //为C头，但不好的C ++ header 
 #undef complex 
 
 #includeiir ++。h
 
命名空间IIR {
 
 ... 
  
  -  
  *** iir ++。h *** / 
 #include< complex> 
 
命名空间IIR {
 
 ... 
  
 
 
 
问题：
 
 
 
 clang在编译时给出以下错误：
  ./ iir.h：570：15：error：expected';'在顶级声明器之后
 double complex iir_response_c（const struct iir_coeff_t * coeff，double freq）; 
 ^ 
; 
  
显然，新的< complex> 导入不发生 - 或 #undef complex 再次发生 - 但我不知道如何。 
解决方案
 < complex.h> ; 
 
 
 
 C ++通过在模式中命名的头文件定义C库兼容性< c ***> 。因此，< complex.h> 的C ++对应名为< ccomplex> 。以下是C ++标准对此的说明：
如果您尝试使用C复数库，您只需要获取C ++。
 
 
 
底线：你根本不能通过C ++编译器运行C复杂数学。至多，您可以使用预处理程序根据 __ cplusplus 生成等效程序。
 
 
 
例如，
  #if __cplusplus 
＃include< complex> 
 typedef std :: complex< double> cdouble; 
 #else 
＃include< complex.h> 
 typedef double complex cdouble; 
 #endif 
  
注意， std :: complex< double> 和 double complex 是布局兼容的每个C ++ 14 [complex.numbers]§26.4/ 4和C11§6.2.5 / 13。目的似乎是，您可以使用 cdouble 用于跨语言函数原型，但严格来说它取决于ABI。
 
 
 
 
 
 
顺便说一下，C ++标准定义了当 #include  时会发生什么，没有任何意义：
所以， #include& h> 应该给你一个全局 :: complex< T> 。这是标准中的缺陷。
 
Notes:
I am compiling on OSX using Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)
Specifically, I am trying to compile a monolithic source from LibIIR, a filter library maintained here by Laurence Withers.
I've already looked at this answer here about using both <complex> and <complex.h> in the same file.
Setup:
I have a file iir.h like so:
#include <complex.h>

#ifdef __cplusplus
extern "C" {
#endif

...
I have C++ source and header files libiir++.cpp and iir++.h like so:
/*** libiir++.cpp ***/
// we need to include "iir.h" first, as it pulls in <complex.h>, which we need
// to take effect before "iir++.h" pulls in <complex>
#include "iir.h"

// now remove the preprocessor definition of complex to _Complex, which is fine
// for the C header but not good for the C++ header
#undef complex

#include "iir++.h"

namespace IIR {

...
-
/*** iir++.h ***/
#include <complex>

namespace IIR {

...
Problem:
clang gives me the following error when compiling:
./iir.h:570:15: error: expected ';' after top level declarator
double complex iir_response_c(const struct iir_coeff_t* coeff, double freq);
              ^
              ;
Evidently, the new <complex> import is not happening--or #undef complex is happening again--but I don't see how. Any advice on what might be going wrong, or what to check?
 解决方案 
<complex.h> is a C header and it is not compatible with C++.
C++ defines C library compatibility through headers named in the pattern <c***>. So, the C++ counterpart to <complex.h> is named <ccomplex>. Here's what the C++ standard has to say about that:
If you attempt to use the C complex number library, you just get the C++ one instead.
Bottom line: you simply cannot run C complex math through a C++ compiler. At best, you can use the preprocessor to generate equivalent programs depending on __cplusplus.
For example,
#if __cplusplus
#   include <complex>
    typedef std::complex< double > cdouble;
#else
#   include <complex.h>
    typedef double complex cdouble;
#endif
Note, std::complex< double > and double complex are layout-compatible per C++14 [complex.numbers] §26.4/4 and C11 §6.2.5/13. The intent seems to be that you can use cdouble for cross-language function prototypes, although strictly speaking it depends on the ABI.
Incidentally, the C++ standard does define what happens when you #include <complex.h>, but it doesn't make any sense:
So, #include <complex.h> should give you a global ::complex<T>. This is a defect in the standard.
                        
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