[R-pkg-devel] [Re] warning: type of ‘zhpevx_’ does not match original declaration [-Wlto-type-mismatch]

[Ivan Krylov]

Dear Pierre L.,

I think that the zhpevxC wrapper, as written, may result in undefined
behaviour:

>    const char *JOBZ = jobz[0];

>    delete[] JOBZ;

>    delete[] Cap;

This could work okay, depending on how the rest of the package is
written, but in general, it is considered a bad idea for linear algebra
routines to deallocate memory they didn't allocate. ("Pointer
ownership is usually retained by the calling code.")

May I suggest once again the idea of writing a Fortran 2003 wrapper
zhpevxC instead of C++? Subroutines defined using iso_c_binding are
guaranteed to follow the C calling convention, and, this being Fortran,
call zhpevx(...) is guaranteed to match the Fortran calling convention,
bringing you the best of both worlds:

https://stat.ethz.ch/pipermail/r-package-devel/2020q3/005710.html

No need to allocate or deallocate memory or provide different
definitions depending on the availability of FC_LEN_T, just make sure
that both prototypes mean the same thing. By the way,
std::complex<double> is guaranteed to match the memory layout of C type
double _Complex and Fortran type complex(kind = c_double_complex) by
the respective standards.

-- 
Best regards,
Ivan