使用 SWIG 作为参数传递给 C 库的错误值 [英] Wrong values passed as parameter to C library using SWIG

问题描述

遵循我的三个 以前 posts，我现在可以将一个托管的结构数组传递给我的包装方法.以下是文件的摘录:

Following my three previous posts, I can now pass a managed array of struct to my wrapped method. Here is an extract from the files:

// packer.i
typedef struct {
  int width; // input
  int height; // input
  frame_t view; // output
  frame_t dest; // output
} image_t;

CSHARP_ARRAYS(image_t, image_t)
%apply image_t INOUT[] { image_t *images }

int pack(image_t *images, int nb_images, parameters_t params);

生成具有此签名的函数:

Which generates a function with this signature:

// packer_cs.cs
public static int pack(image_t[] images, int nb_images, parameters_t arg2)

我这样称呼:

// Program.cs
var files = Directory.GetFiles("./images");
var images = new image_t[files.Length];
for (var f = 0; f < files.Length; f++)
{
    using (var imgInfo = Image.FromFile(files[f]))
    {
        var imgStruct = new image_t()
                        {
                            width = imgInfo.Width,
                            height = imgInfo.Height,
                            dest = new frame_t(),
                            view = new frame_t()
                        };
        images[f] = imgStruct;
    }
}
var result = packer_cs.pack(images, images.Length, new parameters_t());

一切都很好，但是当我运行 pack() 方法时，我遇到了受保护的内存访问问题 (System.AccessViolationException).幸运的是，我可以访问 C 库的源代码，并且一旦启用非托管代码调试，Visual Studio 就会自动打开它进行调试和单步调试.

All is well and done, but when I run the pack() method, I have a protected memory access problem (System.AccessViolationException). Thankfully I have access to the source code of the C library, and Visual Studio automagically opens it for debugging and stepping through as soon as I enable unmanaged code debugging.

因此，如果我在 pack() 函数的开头添加断点，并使用手表检查 images[x]，我可以看到宽度和高度值与提供的内容无关(有时甚至是 0 或负数).这是怎么回事 ?如果我在 C# 端检查我的托管数组，则会正确存储和检索这些值.为什么 C 没有得到正确的值?其他参数(nb_images 和 params)没有任何问题.

So, if I add a breakpoint at the start of the pack() function, and I use a watch to check images[x], I can see that the width and height values have nothing to do with what is provided (sometimes it's even 0 or negative). What's going on ? If I inspect my managed array on the C# side, the values are correctly stored and retrieved. Why doesn't C get the right values ? The other parameters (nb_images and params) don't have any problem.

谢谢！

推荐答案

执行以下操作:

1. 检查 images[f].width 和 height 是否具有您期望的值
2. 如果是，则检查 SWIG 生成的代码以验证这些字段是否已正确复制.
3. 如果通过查看代码无法发现任何问题，则应中断 packer_cs.pack 并使用调试器查看将 C# 数组复制到 C++ 数组的包装器代码，看看有什么问题.

1. Check that images[f].width and height have the values you expect
2. If yes, then check the SWIG-generated code to verify that those fields are properly copied.
3. If you can't spot any problem by looking at the code, you should break on packer_cs.pack and use the debugger to look at the wrapper code that copies the C# array to the C++ array, see what is wrong.

可能是类型映射中的某些内容不正确.一旦您知道那是什么，您就可以将 SWIG 源(csharp_array.i 文件)中的类型映射代码复制到 .i 中的新类型映射，并根据需要进行修复.

It is probably something in the typemaps that is incorrect. Once you know what that is, you can copy the typemaps code from SWIG source (the csharp_array.i file) to a new typemap in your .i and fix as required.

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