CODEWITHSUNDEEP
python-3.xcythonopenal-soft
SeanTolstoyevski
SeanTolstoyevski

Reputation: 149

How to write #define expressions with nested brackets in cython?

C expression:

#define EFX_REVERB_PRESET_GENERIC \
    { 1.0000f, 1.0000f, 0.3162f, 0.8913f, 1.0000f, 1.4900f, 0.8300f, 1.0000f, 0.0500f, 0.0070f, { 0.0000f, 0.0000f, 0.0000f }, 1.2589f, 0.0110f, { 0.0000f, 0.0000f, 0.0000f }, 0.2500f, 0.0000f, 0.2500f, 0.0000f, 0.9943f, 5000.0000f, 250.0000f, 0.0000f, 0x1 }

I want to define this expression in the .pxd file.

I have to pass this expression as parameters to some C functions. So I don't use it for Python.

Source: OpenAL-Soft: https://github.com/kcat/openal-soft/blob/master/include/AL/efx-presets.h#L37

Upvotes: 0

Views: 80

Answers (1)

DavidW
DavidW

Reputation: 30913

It's worth realising that not everything has a direct translation from C to Cython. In this case EFX_REVERB_PRESET_GENERIC can't really be defined using a type because it isn't a type - it's just a collection of brackets and numbers. These brackets and numbers are only valid in a small number of places:

 void other_func(WhateverTheStructIsCalled s);

 void func() {
     WhateverTheStructIsCalled s = EFX_REVERB_PRESET_GENERIC; // OK
     s = EFX_REVERB_PRESET_GENERIC; // wrong - not an initialization
     other_func(EFX_REVERB_PRESET_GENERIC); // also doesn't work
 }

Therefore it doesn't really fit into Cython's model so you can't wrap it directly.

What I'd do is write a small C wrapper yourself. You can do this with Cython's "inline C code" function:

cdef extern from *:
    """
    WhateverTheStructIsCalled get_EFX_REVERB_PRESET_GENERIC(void) {
        WhateverTheStructIsCalled s = EFX_REVERB_PRESET_GENERIC;
        return s;
    }
    """
    WhateverTheStructIsCalled get_EFX_REVERB_PRESET_GENERIC()

Then use get_EFX_REVERB_PRESET_GENERIC() to call this function and get the relevant initialized structure.

Upvotes: 3

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