如何编组一个可变大小的结构数组？C#和C++互操作帮助

Question

我有以下C++结构

struct InnerStruct
{
   int A;
   int B;
};

struct OuterStruct
{
   int numberStructs;
   InnerStruct* innerStructs;
};

还有一个C++函数

OuterStruct getStructs();

我如何将其编组为C#？C#定义的位置

struct OuterStruct {
   InnerStruct[] innerStructs;
};

Answer 1

您必须手动执行此操作,因为无法告诉P/Invoke层要从C++返回值编组多少数据.

struct OuterStruct {
   int numberStructs;
   IntPtr innerStructs;
};

OuterStruct s = getStructs(); // using DllImport
var structSize = Marshal.SizeOf(typeof(InnerStruct));
var innerStructs = new List<InnerStruct>();
var ptr = s.innerStructs;

for (int i = 0; i < s.numberStructs; i++)
{
    innerStructs.Add((InnerStruct)Marshal.PtrToStructure(ptr, 
        typeof(InnerStruct));
    ptr = ptr + structSize;
}

请注意,如果innerStructs要从C#代码中释放内存,则必须CoTaskMemAlloc在C++代码中使用标准分配器- 然后您可以调用Marshal.CoTaskMemFreefree innerStructs.