ma <mabdelka...@gmail.com> wrote:
>If I have this struct in C:
>
>struct spam {
> int ham;
> char foo;
>};
>
>
>if I have this declaration:
>struct spam s_;
>
>If I wanted to pass a reference to a function of s_'s foo character, I
>can do something like this:
>
>somefunc(&s_.foo)
>
>How do I do the same thing in ctypes?
>ctypes.addressof(s_) + ctypes.sizeof(spam.foo)*(1)
See ctypes.create_string_buffer().
To unpack the struct elements received from the C function, use
struct.unpack().
Here some example:
def rssiam_volt_Q(self):
'''Output Voltage Query
'''
query_buffer = ctypes.create_string_buffer(8)
self.rssiam_32_dll.rssiam_volt_Q.argtypes = [ctypes.c_long,
ctypes.c_char_p]
result = self.rssiam_32_dll.rssiam_volt_Q(self.session,
query_buffer)
if result != VI_SUCCESS:
raise IOError, 'rssiam_volt_Q: result = %d' % result
return(struct.unpack('d', query_buffer.raw)[0])
In this case, it is a 64 bits float (= double) value that is returned by
reference (query_buffer).
Attention, struct.unpack() returns a tuple, even when there is only a
single element to extract from the buffer.
Regards,
Günther
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