我正在嘗試使用來自C#的非托管API,并將頭撞墻. (關(guān)于PInvoke,我是個(gè)初學(xué)者.)

頭文件的相關(guān)部分如下所示：

#define CTAPICALL       __stdcall
#ifdef __cplusplus
    extern "C" {
#endif

extern  BOOL    CTAPICALL   ctTagReadEx(HANDLE,LPCSTR,LPSTR,DWORD,CT_TAGVALUE_ITEMS*);      /* read extended data from tag          */

#ifdef __cplusplus
}
#endif

CT_TAGVALUE_ITEMS如下所示：

typedef struct
{
    DWORD                   dwLength;                           /* size, in bytes, of this structure    */
    unsigned __int64        nTimestamp;                         /*  timestamp                           */
    unsigned __int64        nValueTimestamp;                    /*  value timestamp                     */
    unsigned __int64        nQualityTimestamp;                  /*  quality timestamp                   */
    BYTE                    bQualityGeneral;                    /*  quality general                     */
    BYTE                    bQualitySubstatus;                  /*  quality substatus                   */
    BYTE                    bQualityLimit;                      /*  quality limit                       */
    BYTE                    bQualityExtendedSubstatus;          /*  quality extended substatus          */
    UINT                    nQualityDatasourceErrorCode;        /*  quality datasource error            */
    BOOLEAN                 bOverride;                          /*  quality override flag               */
    BOOLEAN                 bControlMode;                       /*  quality control mode flag           */
}   CT_TAGVALUE_ITEMS;

我的C#方法聲明：

    [DllImport("ctapi.dll", SetLastError = true)]
    public static extern bool ctTagReadEx(
        IntPtr hCTAPI,
        [MarshalAs(UnmanagedType.LPStr)] string tag,
        [MarshalAs(UnmanagedType.LPStr)] System.Text.StringBuilder value,
        int length,
        CtTagValueItems tagValueItems);

C#結(jié)構(gòu)：

[StructLayout(LayoutKind.Sequential)]
public struct CtTagValueItems
{
    public int dwLength;
    public ulong nTimestamp;
    public ulong nValueTimestamp;
    public ulong nQualityTimestamp;
    public byte bQualityGeneral
    public byte bQualitySubstatus;
    public byte bQualityLimit;
    public byte bQualityExtendedSubstatus;
    public uint nQualityDatasourceErrorCode;
    public uint bOverride;
    public uint bControlMode;
}

當(dāng)我這樣調(diào)用它時(shí)(從以x86構(gòu)建的測試程序集中),我得到一個(gè)System.AccessViolationException：嘗試讀取或?qū)懭胧鼙Ｗo(hù)的內(nèi)存：

StringBuilder valueBuilder = new StringBuilder(300);
CtTagValueItems tagValueItems = new CtTagValueItems {dwLength = Marshal.SizeOf(typeof (CtTagValueItems))};
bool ok = CTAPI.ctTagReadEx(new IntPtr(handle), "TIC_Hold_PV", valueBuilder, valueBuilder.Capacity, tagValueItems);

我一直在嘗試各種事情,例如使用LayoutKind.Explicit和/或CallingConvention = CallingConvention.Cdecl,但無濟(jì)于事.

有人可以幫忙嗎,？

解決方法:

>為什么將UINT映射為ushort.它沒有4個(gè)字節(jié)嗎？
>原生BOOLEAN類型映射為4個(gè)字節(jié),即AFAIK.
>您需要通過ref(作為類或ref)傳遞CtTagValueItems.
>檢查呼叫約定.
>檢查注釋中寫的內(nèi)容.