如何处理红宝石ffi宝石中的红宝石阵列? [英] How do I handle ruby arrays in ruby ffi gem?

问题描述

我想使用ruby ffi gem调用一个c函数，该函数具有一个数组作为输入变量，而输出是一个数组.也就是说，c函数如下所示:

I want to use the ruby ffi gem to call a c function which has an array as an input variable and the output is an array. That is, the c function looks like:

double *my_function(double array[], int size)

我创建的红宝石绑定为:

I have created the ruby binding as:

module MyModule
  extend FFI::Library
  ffi_lib 'c'
  ffi_lib 'my_c_lib'
  attach_function :my_function, [:pointer, int], :pointer

我想用以下类似的红宝石代码拨打电话:

I will like to make a call in ruby code like:

result_array = MyModule.my_function([4, 6, 4], 3)

我该怎么办?

推荐答案

假设这是您希望在ruby脚本中使用的库，将其命名为my_c_lib.c:

Let's say that this is the library you wish to use in your ruby script, call it my_c_lib.c:

#include <stdlib.h>

double *my_function(double array[], int size)
{
  int i = 0;
  double *new_array = malloc(sizeof(double) * size);
  for (i = 0; i < size; i++) {
    new_array[i] = array[i] * 2;
  }

  return new_array;
}

您可以像这样编译它:

$ gcc -Wall -c my_c_lib.c -o my_c_lib.o
$ gcc -shared -o my_c_lib.so my_c_lib.o

现在，可以在您的红宝石代码(my_c_lib.rb)中使用它了:

Now, it's ready to use in in your ruby code (my_c_lib.rb):

require 'ffi'

module MyModule
  extend FFI::Library

  # Assuming the library files are in the same directory as this script
  ffi_lib "./my_c_lib.so"

  attach_function :my_function, [:pointer, :int], :pointer
end

array = [4, 6, 4]
size = array.size
offset = 0

# Create the pointer to the array
pointer = FFI::MemoryPointer.new :double, size

# Fill the memory location with your data
pointer.put_array_of_double offset, array

# Call the function ... it returns an FFI::Pointer
result_pointer = MyModule.my_function(pointer, size)

# Get the array and put it in `result_array` for use
result_array = result_pointer.read_array_of_double(size)

# Print it out!
p result_array

这是运行脚本的结果:

$ ruby my_c_lib.rb
[8.0, 12.0, 8.0]

有关内存管理的说明...来自文档 https://github.com/ffi /ffi/wiki/Pointers :

A note on memory management...from the docs https://github.com/ffi/ffi/wiki/Pointers:

FFI :: MemoryPointer类分配具有自动垃圾收集功能的本机内存作为甜味剂.当MemoryPointer超出范围时，将在垃圾回收过程中释放内存.

The FFI::MemoryPointer class allocates native memory with automatic garbage collection as a sweetener. When a MemoryPointer goes out of scope, the memory is freed up as part of the garbage collection process.

因此您不必直接致电pointer.free.另外，只是为了检查是否必须手动释放result_pointer，我在打印提取数组后调用了result_pointer.free并得到了此警告

So you shouldn't have to call pointer.free directly. Also, just to check whether you had to manually free result_pointer, I called result_pointer.free after printing extracting the array and got this warning

warning: calling free on non allocated pointer #<FFI::Pointer address=0x007fd32b611ec0>

所以看起来您也不必手动释放result_pointer.

So it looks like you don't have to manually free result_pointer either.

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