调用c ++ dll函数从c#返回char*.不能使用DllImport()

Question

我有一个带有2个函数的c ++ dll

const char* getVersionText1(void);
void        getVersionText2(const char** res);

两个函数都返回一个描述产品版本的字符串.第一个函数将它作为const char*返回(这意味着它在内部分配和处理它),第二个函数获取一个指向char*的指针,并将其设置为指向描述版本的char*.

我想从C#调用这些函数并显示文本.我不能使用[dllimport ...]样式,因为调用函数的顺序很重要.我首先调用构造函数而不是getVersion,最后是析构函数.所以必须先将dll加载到内存中.

您能否发布几行代码打印两种功能的文本.我是C#的新手,很抱歉如果你发现我的代码有问题我试过了

static class NativeMethods{
    [DllImport("kernel32.dll")]
    public static extern IntPtr LoadLibrary(string dllToLoad);
    [DllImport("kernel32.dll")]
    public static extern IntPtr GetProcAddress(IntPtr hModule, string procedureName);
    [DllImport("kernel32.dll")]
    public static extern bool FreeLibrary(IntPtr hModule);
}
class Program{
    // Define function pointers to entires in DLL
    [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate IntPtr getVersionText1();
    [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate void getVersionText2(IntPtr );
    static void Main(string[] args){
        // Pointers to functions of DLL.
        getVersionText1 f1;
        getVersionText2 f2;
        IntPtr pDll = NativeMethods.LoadLibrary("p:\\my.dll");
        IntPtr pAddressOfFunctionToCall;
        pAddressOfFunctionToCall = NativeMethods.GetProcAddress(pDll, "getVersionText1 ");
        f1 = (getVersionText1)Marshal.GetDelegateForFunctionPointer(pAddressOfFunctionToCall, typeof(getVersionText1));
        pAddressOfFunctionToCall = NativeMethods.GetProcAddress(pDll, "getVersionText2 ");
        f2 = (getVersionText2)Marshal.GetDelegateForFunctionPointer(pAddressOfFunctionToCall, typeof(getVersionText2));

        // Here I don't know what to do. It doesn't work ????
        IntPtr verText = f1();
        String s = Marshal.PtrToStringAuto(verText);
        Console.WriteLine(s);   // Doesnt work
        // And how to use the second function. How do I sent a pointer to char* ???
    }
}

Answer 1

如果C++库函数返回时char*,C#代码将它视为IntPtr和Marshal.PtrToStringAnsi()将其转换成C# string.

IntPtr verText = f1();
string s = Marshal.PtrToStringAnsi(verText);
Console.WriteLine(s);

Answer 2

这是一种打电话的方式.可能有更短的替代品自动执行utf8 /字符串转换.

[DllImport("mydll.dll")]
public static extern IntPtr getVersionText1(void);
public string getVersionTextConst()
{
    IntPtr ptr = getVersionText1();
    // assume returned string is utf-8 encoded
    return PtrToStringUtf8(ptr);
}

[DllImport("mydll.dll")]
public static extern void getVersionText2(out IntPtr res);
public string getVersionTextConst()
{
    IntPtr ptr;
    getVersionText2(ptr);
    // assume returned string is utf-8 encoded
    String str = PtrToStringUtf8(ptr);
    // call native DLL function to free ptr
    // if no function exists, pinvoke C runtime's free()
    return str;
}

private static string PtrToStringUtf8(IntPtr ptr) // aPtr is nul-terminated
{
    if (ptr == IntPtr.Zero)
        return "";
    int len = 0;
    while (System.Runtime.InteropServices.Marshal.ReadByte(ptr, len) != 0)
        len++;
    if (len == 0)
        return "";
    byte[] array = new byte[len];
    System.Runtime.InteropServices.Marshal.Copy(ptr, array, 0, len);
    return System.Text.Encoding.UTF8.GetString(array);
}