On 9/2/17, eryk sun <eryk...@gmail.com> wrote:
> On Fri, Sep 1, 2017 at 3:23 AM, Peter Otten <__pete...@web.de> wrote:
>>
>> I think you have to specify the types yourself:
>>
>>>>> import ctypes
>>>>> libm = ctypes.cdll.LoadLibrary("libm.so")
>>>>> libm.sqrt(42)
>> 0
>>>>> libm.sqrt.argtypes = [ctypes.c_double]
>>>>> libm.sqrt.restype = ctypes.c_double
>>>>> libm.sqrt(42)
>> 6.48074069840786
>
> On POSIX systems, use ctypes.util.find_library('m'), which, for
> example, resolves to "libm.so.6" in Ubuntu Linux 16.04. On the same
> system, "libm.so" is an ld script that's used by the compile-time
> linker.
>
> $ cat /usr/lib/x86_64-linux-gnu/libm.so
> /* GNU ld script
> */
> OUTPUT_FORMAT(elf64-x86-64)
> GROUP ( /lib/x86_64-linux-gnu/libm.so.6
> AS_NEEDED (
> /usr/lib/x86_64-linux-gnu/libmvec_nonshared.a
> /lib/x86_64-linux-gnu/libmvec.so.1 ) )
>
> The runtime linker doesn't know how to handle this script.
>
> >>> ctypes.CDLL('libm.so')
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> File "/usr/lib/python3.5/ctypes/__init__.py",
> line 347, in __init__
> self._handle = _dlopen(self._name, mode)
> OSError: /usr/lib/x86_64-linux-gnu/libm.so: invalid ELF header
Peter and Eryk thanks very much! :)
BTW julia on ubuntu 16.04 could do it ->
julia> result = ccall((:sqrt, "libm"), Cdouble, (Cdouble,), 1.3)
1.140175425099138
but I am afraid that it probably uses some llvm's magic so it could
not help to solve this problem in ctypes...
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