stackoverflow-pointers-ref-in-golang

This project was created to answer a question about exchange pointer between python and golang.

How do

To build shared-library

$ export GOPATH=$(pwd) 
$ go build -o libtest.so -buildmode=c-shared pyrefs

Tests

To Golang-based test:

$ export GOPATH=$(pwd) 
$ go run src/pyrefs/function.go

To C-based test:

clang -o goinc.test goin.c -L. -ltest

In MacOS-10.12, to C-based test:

clang -o goinc.test goin.c -L. -L/usr/lib -ltest

To Python-based test:

python goin.py

About problem:

The developer needs call a golang function from python passing float and int type params and returning an slice, but occour an unkwnow error.

Source: https://stackoverflow.com/questions/51845092/how-to-return-an-array-from-golang-to-python-using-ctypes/51912417

The solution:

The developer used the code follow to set restype to lib:

lib.Function.restype = ndpointer(dtype = c_double, shape = (N,))

In this case restype is a pointer type (by Numpy doc):

def ndpointer(dtype=None, ndim=None, shape=None, flags=None)

[others texts]

Returns

klass : ndpointer type object

A type object, which is an _ndtpr instance containing dtype, ndim, shape and flags information.

The appropriated type in Golang to treat it is unsafe.Pointer.

However yet has a problem: slice pointer like result. This violate rule 2 of Rules for passing pointers between Go and C:

C code may not keep a copy of a Go pointer after the call returns.

The solution is to convert unsafe.Pointer to uintptr.

More details about solution: https://stackoverflow.com/questions/51845092/how-to-return-an-array-from-golang-to-python-using-ctypes/51912417#51912417