Just a simple question,having this:
fftw_complex *H_cast;
H_cast = (fftw_complex*) fftw_malloc(sizeof(fftw_complex)*M*N);
what is the difference between:
H_cast= reinterpret_cast<fftw_complex*> (H);
and
H_cast= reinterpret_cast<fftw_complex*> (&H);
Thanks so much in advance
Antonio
Answer to current question
The difference is that they do two completely different things!
Note: you do not tell us what H is, so it's impossible to answer the question with confidence. But general principles apply.
For the first case to be sensible code, H should be a pointer (typed as void* possibly?) to a fftw_complex instance. You would do this to tell the compiler that H is really a fftw_complex*, so you can then use it.
For the second case to be sensible code, H should be an instance of a class with a memory layout identical to that of class fftw_complex. I can't think of a compelling reason to put yourself in this situation, it is very unnatural. Based on this, and since you don't give us information regarding H, I think it's almost certainly a bug.
Original answer
The main difference is that in the second case you can search your source code for reinterpret_cast (and hopefully ensure that every use is clearly documented and a necessary evil).
However, if you are casting from void* to another pointer type (is this the case here?) then it's preferable to use static_cast instead (which can also be easily searched for).