通过引用传递结构导致AccessViolationException

问题描述

限时删除！！

还有另一个我的P/调用问题！我有这个C函数:

Yet another one of my P/Invoke questions! I have this C function:

int _ei_x_new(ei_x_buff* x);

本质上，它将初始化一个新的缓冲区结构.在C#中，我有这个:

Essentially, it initializes a new buffer struct. In C#, I have this:

[DllImport(EIDLL, EntryPoint = "_ei_x_new")]
public static extern int ei_x_new(out ei_x_buff x);

ei_x_buff非常简单:

typedef struct ei_x_buff_TAG {
    char* buff;
    int buffsz;
    int index;
} ei_x_buff;

[StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct ei_x_buff {
    [MarshalAsAttribute(UnmanagedType.LPStr)]
    public string buff;
    public int buffsz;
    public int index;
}

但是当我这样做时:

ei_x_buff buffer;
Ei.ei_x_new(out buffer);

我收到一个 AccessViolationException :

我需要分配一些内存吗?这是一段简单的代码，我看不到任何明显的问题.

Do I need to alloc some memory or something? It's such a simple piece of code that I can't see any glaring problems with it.

_ei_x_new的本地代码:

// In my wrapper library
DLL_EXPORT int _ei_x_new(ei_x_buff* x) {
    return ei_x_new(x);
}

// In external library being wrapped
int ei_x_extra = 100;

int ei_x_new(ei_x_buff* x)
{
    x->buff = malloc(ei_x_extra);
    x->buffsz = ei_x_extra;
    x->index = 0;
    return x->buff != NULL ? 0 : -1;
}

推荐答案

事物的结合

• 要在双向(进出本机函数)中整理数据，请在PInvoke签名中使用not ref
• 您能否发布本机签名，因为它们可能是定义问题.特别是buff成员

编辑

只是为了消除一种可能性，请将buff成员切换为没有属性的IntPtr类型.如果这不会导致崩溃，则可能是字符串类型存在编组问题.

Just to eliminate one possibility, switch the buff member to be typed IntPtr with no attributes. If that doesn't cause a crash then it's likely a marshalling issue with the string type.

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