c# - 通过引用传递到非托管 C DLL 函数后，结构保持不变

Question

我正在用 C# 为非托管 C DLL 编写一个包装器。在 DLL 中，我有以下方法返回指针结构(结构代码接近帖子末尾):

struct zint_symbol *ZBarcode_Create()
{
    struct zint_symbol *symbol = (struct zint_symbol*)calloc(1, sizeof(struct zint_symbol));

    if (!symbol) return NULL;

    symbol->symbology = BARCODE_CODE128;
    strcpy(symbol->fgcolour, "000000");
    strcpy(symbol->bgcolour, "ffffff");
    strcpy(symbol->outfile, "out.png");
    symbol->scale = 1.0;
    symbol->option_1 = -1;
    symbol->option_3 = 928; // PDF_MAX
    symbol->show_hrt = 1; // Show human readable text
    return symbol;
}

我使用的外部方法是:

extern struct zint_symbol* ZBarcode_Create(void);
extern int ZBarcode_Encode_and_Buffer(struct zint_symbol *symbol, unsigned char *input, int length, int rotate_angle);
extern int ZBarcode_Encode_and_Print(struct zint_symbol *symbol, unsigned char *input, int length, int rotate_angle);

ZBarcode_Encode_and_Buffer 渲染图像并将位图保存在我的结构中名为 bitmap 的变量中。 ZBarcode_Encode_and_Print 渲染图像并将其保存到文件系统。成功时它们都会返回 0，失败时返回 1-8 之间的数字。每次对我来说，他们都返回 0。

我的 C# 如下所示:

[DllImport("zint.dll", EntryPoint = "ZBarcode_Create", CallingConvention = CallingConvention.Cdecl)]
public extern static IntPtr Create();

[DllImport("zint.dll", EntryPoint = "ZBarcode_Encode_and_Buffer", CallingConvention = CallingConvention.Cdecl)]
public extern static int EncodeAndBuffer(
 ref zint_symbol symbol,
 string input,
 int length,
 int rotate_angle);

[DllImport("zint.dll", EntryPoint = "ZBarcode_Encode_and_Print", CallingConvention = CallingConvention.Cdecl)]
public extern static int EncodeAndPrint(
 ref zint_symbol symbol,
 string input,
 int length,
 int rotate_angle);

public static void Render()
{
    // call DLL function to generate pointer to initialized struct
    zint_symbol s = (zint_symbol)

    // generate managed counterpart of struct
    Marshal.PtrToStructure(ZintLib.Create(), typeof(zint_symbol));

    // change some settings
    s.symbology = 71;
    s.outfile = "baro.png";
    s.text = "12345";

    String str = "12345";

    // DLL function call to generate output file using changed settings -- DOES NOT WORK --
    System.Console.WriteLine(ZintLib.EncodeAndBuffer(ref s, str, str.Length, 0));

    // DLL function call to generate output file using changed settings -- WORKS --
    System.Console.WriteLine(ZintLib.EncodeAndPrint(ref s, str, str.Length, 0));

    // notice that these variables are set in ZBarcode_Create()?
    Console.WriteLine("bgcolor=" + s.bgcolour + ", fgcolor=" + s.fgcolour + ", outfile=" + s.outfile);

    // these variables maintain the same values as when they were written to in ZBarcode_Create().
    if (s.errtxt != null)
        Console.WriteLine("Error: " + s.errtxt);
    else
        Console.WriteLine("Image size rendered: " + s.bitmap_width + " x " + s.bitmap_height);
}

s 中的所有变量保持不变，即使 DLL 应该更改其中一些变量，例如位图、bitmap_width、bitmap_height 等

我怀疑内存中有两份zint_symbol副本；我的 C# 代码具有的一个(由 ZintLib.Create() 创建)和 DLL 正在写入的另一个文件。不过，我确信该库可以正常工作。

C 结构:

struct zint_symbol {
    int symbology;
    int height;
    int whitespace_width;
    int border_width;
    int output_options;
#define ZINT_COLOUR_SIZE 10
    char fgcolour[ZINT_COLOUR_SIZE];
    char bgcolour[ZINT_COLOUR_SIZE];
    char outfile[FILENAME_MAX];
    float scale;
    int option_1;
    int option_2;
    int option_3;
    int show_hrt;
    int input_mode;
#define ZINT_TEXT_SIZE  128
    unsigned char text[ZINT_TEXT_SIZE];
    int rows;
    int width;
#define ZINT_PRIMARY_SIZE  128
    char primary[ZINT_PRIMARY_SIZE];
#define ZINT_ROWS_MAX  178
#define ZINT_COLS_MAX  178
    unsigned char encoded_data[ZINT_ROWS_MAX][ZINT_COLS_MAX];
    int row_height[ZINT_ROWS_MAX]; /* Largest symbol is 177x177 QR Code */
#define ZINT_ERR_SIZE   100
    char errtxt[ZINT_ERR_SIZE];
    char *bitmap;
    int bitmap_width;
    int bitmap_height;
    struct zint_render *rendered;
};

C# 结构:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    public struct zint_symbol
    {
        public int symbology;
        public int height;
        public int whitespace_width;
        public int border_width;
        public int output_options;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 10)]
        public String fgcolour;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 10)]
        public String bgcolour;


        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 100)]
        public string errtxt;

        public float scale;

        public int option_1;
        public int option_2;
        public int option_3;
        public int show_hrt;
        public int input_mode;
        public int rows;
        public int width;
        public int bitmap_width;
        public int bitmap_height;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
        public string text;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
        public string primary;

        [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.U1, SizeConst = 31684)]
        public byte[] encoded_data;

        [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.I4, SizeConst = 178)]
        public int[] row_height;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
        public string outfile;

        public IntPtr bitmap;
        public IntPtr rendered;
    }

我写了一个小Windows forms example (DLL 在那里，还有 available here 。库文档(第 18/61 页解释了结构变量) is available here 和整个 C 源代码可用 here (zint-2.4.3.tar.gz) 。特别感兴趣的文件是 zint.h、library .c 和 datamatrix.c。C 源代码是相同版本的 DLL。

编辑

结构布局似乎不匹配。 C 中的 sizeof(zint_symbol) != C# 中的 sizeof(zint_symbol)。

Answer 1

你这里有一个奇怪的错误:

[MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.U1, SizeConst = 25454)]
public byte[] encoded_data;

.h 文件中的内容是:

#define ZINT_ROWS_MAX 178
#define ZINT_COLS_MAX 178
    uint8_t encoded_data[ZINT_ROWS_MAX][ZINT_COLS_MAX];

以同样的方式声明它:

[MarshalAs(UnmanagedType.ByValArray, SizeConst = 178 * 178)]
public byte[] encoded_data;

还有一个错误，FILENAME_MAX 是 260:

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
public string outfile;

现在你应该得到一个正确的匹配:

static void Main(string[] args) {
    var len = Marshal.SizeOf(typeof(zint_symbol));              // 33100
    var offs = Marshal.OffsetOf(typeof(zint_symbol), "errtxt"); // 32984
}

在 C 测试程序中:

#include <stddef.h>
//...
int main()
{
    size_t len = sizeof(zint_symbol);                // 33100
    size_t offs = offsetof(zint_symbol, errtxt);     // 32984
    return 0;
}