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POPython is passing 32bit pointer address to C functions
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16635259
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16635399
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4
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2013-05-19T13:39:39.763
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2017-09-11T08:26:11.250
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2013-05-19T18:52:05.860
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217470
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217470
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1
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8
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3112
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I would like to call my C functions within a shared library from Python scripts. Problem arrises when passing pointers, the 64bit addresses seem to be truncated to 32bit addresses within the called function. Both Python and my library are 64bit. The example codes below demonstrate the problem. The Python script prints the address of the data being passed to the C function. Then, the address received is printed from within the called C function. Additionally, the C function proves that it is 64bit by printing the size and address of locally creating memory. If the pointer is used in any other way, the result is a segfault. CMakeLists.txt <pre><code>cmake_minimum_required (VERSION 2.6) add_library(plate MODULE plate.c) </code></pre> plate.c <pre><code>#include <stdio.h> #include <stdlib.h> void plate(float *in, float *out, int cnt) { void *ptr = malloc(1024); fprintf(stderr, "passed address: %p\n", in); fprintf(stderr, "local pointer size: %lu\n local pointer address: %p\n", sizeof(void *), ptr); free(ptr); } </code></pre> test_plate.py <pre><code>import numpy import scipy import ctypes N = 3 x = numpy.ones(N, dtype=numpy.float32) y = numpy.ones(N, dtype=numpy.float32) plate = ctypes.cdll.LoadLibrary('libplate.so') print 'passing address: %0x' % x.ctypes.data plate.plate(x.ctypes.data, y.ctypes.data, ctypes.c_int(N)) </code></pre> Output from python-2.7 <blockquote> In [1]: run ../test_plate.py passing address: 7f9a09b02320 passed address: 0x9b02320 local pointer size: 8 local pointer address: 0x7f9a0949a400 </blockquote>
Tags
<python><c><macos><cmake><ctypes>
Title
Python is passing 32bit pointer address to C functions
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