c# - 在 C# 中有效使用指向任意内存位置的原始指针

Question

在下面的代码中，我构建了一个指向位于任意内存位置的结构的指针:

[StructLayout(LayoutKind.Explicit)]
public struct S
{
    [FieldOffset(0)] int f0;
    [FieldOffset(4)] int f4;

    public static void Main() {
        unsafe {
            S* rawPtr = (S*)0x1234;
            rawPtr->f0 = 42;
        }
    }
}

如果我将 f4 的类型更改为 object 而不是 int，我会收到错误 Compiler Error CS0208: Cannot take the address of, get the size of, or declare a pointer to a managed type ('type') .

struct S 上允许在 CIL(而不仅仅是 C#)级别在该类型上构建指针的约束是什么？

This page on MSDN说 sbyte, byte, short, ushort, int, uint , long, ulong, char, float, double,允许使用 decimal、bool、枚举和指针，以及“仅包含非托管类型字段的用户定义结构类型”，但未指定非托管类型类型是。

Answer 1

我无法在网上找到易于导航的 ECMA-335 版本，但是 ECMA-334 paragraph 27.2说:

An unmanaged-type is any type that isn’t a reference-type, a type-parameter, or a generic struct-type and contains no fields whose type is not an unmanaged-type. In other words, an unmanaged-type is one of the following:

• sbyte, byte, short, ushort, int, uint, long, ulong, char, float, double, decimal, or bool.

• Any enum-type.

• Any pointer-type.

• Any non-generic user-defined struct-type that contains fields of unmanaged-types only.

[Note: Constructed types and type-parameters are never unmanaged-types. end note]

结构的打包模式似乎与这种区别无关。