从Julia调用Fortran子例程.数组有效，但整数无效 [英] Calling Fortran subroutine from Julia. Arrays work, but integers don't

问题描述

我有一个简单的Fortran 90程序:

I have this simple Fortran 90 program:

subroutine apc_wrapper(i, j, k)
implicit none

integer*8, intent(in) :: i, j
integer*8, intent(out) :: k
double precision t

k = i + js 
end subroutine

编译为共享库

gfortran -O2 -shared -fPIC apc_wrapper.f90 -o apc_wrapper.so

现在，我想从Julia中调用此子例程，并使用所有整数参数，例如

Now, I want to call this subroutine from Julia, with all integer arguments, like this

i = 2
j = 3
k = 0

ccall( (:apc_wrapper_, "./apc_wrapper.so"), Void, (Ptr{Int64}, Ptr{Int64}, Ptr{Int64}), &i, &j, &k)

但是它不起作用. k不会更改其值，并继续求值为0.

But it won't work. k won't change its value and keep evaluating to 0.

但是，如果我这样做

 i = 2
 j = 3
 kk = [0]

 ccall( (:apc_wrapper_, "./apc_wrapper.so"), Void, (Ptr{Int64}, Ptr{Int64}, Ptr{Int64}), &i, &j, kk)

也就是说，使用数组存储输出，它可以正常工作！调用该子例程后，kk计算为

That is, use an array to store the output, it works! After calling the subroutine, kk evaluates to

 1-element Array{Int64,1}:
 5

我根本没有更改Fortran代码，它甚至都不知道它是在处理数组，只是一块内存.

And I didn't change the Fortran code at all, it didn't even know it was dealing with an array, just a block of memory.

因此，如果Fortran能够读取内存块(i和j正确显示为红色)，为什么不能写入它们?

So, if Fortran is able to read blocks of memory (i and j were properly red) why isn't able to write into them?

我对此没有任何问题.实际上，我想使用数组作为输出，但是这种行为令我感到惊讶.

I don't have any problem with this. Actually, I want to use an array as output but still, this behavior surprised me.

推荐答案

Julia是一种快节奏的开发语言，事实证明&variable语法已被弃用. 这是执行此操作的正确方法:

Well, Julia is a fast-paced developing language and it turns out that the &variable syntax is deprecated. This would be the proper way to do this:

i = 2
j = 3
k = 0
i_ref = Ref{Int64}(i)
j_ref = Ref{Int64}(j)
k_ref = Ref{Int64}(k)

ccall( (:apc_wrapper_, "./apc_wrapper.so"), Void,
(Ref{Int64}, Ref{Int64}, Ref{Int64}),
i_ref, j_ref, k_ref)

，然后k_ref.x将计算为5.

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