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Better C++ support (#254) #255

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14 changes: 10 additions & 4 deletions api/fftw3.h
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Expand Up @@ -50,16 +50,22 @@
#include <stdio.h>

#ifdef __cplusplus
# if __cplusplus >= 201103L && defined(FFTW_cpp_complex)
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@LecrisUT LecrisUT Dec 31, 2022

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Add these to cmake (and autotools)

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@stevengj stevengj Jan 1, 2023

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You wouldn't need them for compiling FFTW itself…

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@LecrisUT LecrisUT Jan 2, 2023 •
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Oh, good point. But still they need to be included in cmake export and pkg-config. Or at least documented somewhere

Edit: This could look like:

target_compile_definitions(${fttw_libs} $<$<AND:INSTALL_INTERFACE,CMAKE_CXX_COMPILER>:FFTW_cpp_complex>)

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@stevengj stevengj Jan 2, 2023

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They wouldn't be in pkg-config etcetera because you would need to enable this API in manually user code — it can't be turned on automatically, since that would break backwards compatibility. Definitely would need docs, however.

# include <complex>
# define FFTW_DEFINE_COMPLEX(R, C) typedef ::std::complex<R> C
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@stevengj stevengj Feb 9, 2022 •
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Naive question: What is the difference between ::std::complex and std::complex here?

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@hjmjohnson hjmjohnson Sep 5, 2025

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The :: at the beginning is the global scope resolution operator.
• It means: “start looking from the global namespace, then go into std, then into complex.”
• It is equivalent to std::complex, unless you’ve (accidentally or intentionally) declared another std namespace inside some nested scope.

•	In practice, you almost always just use std::complex.
•	The form ::std::complex is rarely needed, but can be used defensively in highly templated code or when writing library internals, to make sure you always mean the standard-library std::complex and not some shadowed name.

# endif
extern "C"
{
#endif /* __cplusplus */

#ifndef FFTW_DEFINE_COMPLEX
/* If <complex.h> is included, use the C99 complex type. Otherwise
define a type bit-compatible with C99 complex */
#if !defined(FFTW_NO_Complex) && defined(_Complex_I) && defined(complex) && defined(I)
# define FFTW_DEFINE_COMPLEX(R, C) typedef R _Complex C
#else
# define FFTW_DEFINE_COMPLEX(R, C) typedef R C[2]
# if !defined(FFTW_NO_Complex) && defined(_Complex_I) && defined(complex) && defined(I)
# define FFTW_DEFINE_COMPLEX(R, C) typedef R _Complex C
# else
# define FFTW_DEFINE_COMPLEX(R, C) typedef R C[2]
# endif
#endif

#define FFTW_CONCAT(prefix, name) prefix ## name
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