C#从CPP调用参数数目未知的CPP函数

我在CPP中有一个具有以下原型的函数：

char* complexFunction(char* arg1, ...);

我使用DLLImport属性从C#导入它。 问题是: 如何在C#（DLLImport属性下）中定义原型？ 如何将参数传递到此函数？

---

谢谢

这就是所谓的可变函数。关于P/Invoke对它们的支持的信息非常少，下面是我发现的

我找不到直接

DllImport

一个参数数量可变的函数的方法。我必须

DllImport

将参数的所有变体作为不同的重载

让我们举个例子。它在

winuser.h

中具有以下原型：

int WINAPIV wsprintf(      
    LPTSTR lpOut,
    LPCTSTR lpFmt,
    ...);

它可以从C#开始使用，如下所示：

using System;
using System.Text;
using System.Runtime.InteropServices;

class C {

  // first overload - varargs list is single int
  [DllImport("user32.dll", CallingConvention=CallingConvention.Cdecl)]
  static extern int wsprintf(
    [Out] StringBuilder buffer,
    string format,
    int arg);

  // second overload - varargs list is (int, string)
  [DllImport("user32.dll", CallingConvention=CallingConvention.Cdecl)]
  static extern int wsprintf(
    [Out] StringBuilder buffer,
    string format,
    int arg1,
    string arg2);

  public static void Main() {
    StringBuilder buffer = new StringBuilder();
    int result = wsprintf(buffer, "%d + %s", 42, "eggs!");
    Console.WriteLine("result: {0}\n{1}", result, buffer);
  }
}

using System;
using System.Text;
using System.Runtime.InteropServices;

class C {

  [DllImport("your.dll",
             CallingConvention=CallingConvention.Cdecl,
             CharSet=CharSet.Ansi)]
  static extern IntPtr complexFunction(
    string format,
    int arg1, int arg2);

  [DllImport("your.dll", CallingConvention=CallingConvention.Cdecl)]
  static extern void free(IntPtr p);

  public static void Main() {
    IntPtr pResult = complexFunction("%d > %s", 2, 1);
    string sResult = Marshal.PtrToStringAnsi(pResult);
    free(pResult);
    Console.WriteLine("result: {0}", sResult);
  }
}

现在来解决您的

complexFunction

char* complexFunction(char* arg1, ...);

它的varargs列表应该以相同的方式处理：通过提供所有有用的重载。但还有另一个复杂因素——返回类型。我假设

complexFunction

分配并返回

char

的数组。在这种情况下，调用方很可能负责数组的释放。为了实现这一点，您还应该导入释放例程，我们将其称为

voidfree（void*）

假设所有这些都是假设的，使用

complexFunction

的C#代码将如下所示：

using System;
using System.Text;
using System.Runtime.InteropServices;

class C {

  // first overload - varargs list is single int
  [DllImport("user32.dll", CallingConvention=CallingConvention.Cdecl)]
  static extern int wsprintf(
    [Out] StringBuilder buffer,
    string format,
    int arg);

  // second overload - varargs list is (int, string)
  [DllImport("user32.dll", CallingConvention=CallingConvention.Cdecl)]
  static extern int wsprintf(
    [Out] StringBuilder buffer,
    string format,
    int arg1,
    string arg2);

  public static void Main() {
    StringBuilder buffer = new StringBuilder();
    int result = wsprintf(buffer, "%d + %s", 42, "eggs!");
    Console.WriteLine("result: {0}\n{1}", result, buffer);
  }
}

using System;
using System.Text;
using System.Runtime.InteropServices;

class C {

  [DllImport("your.dll",
             CallingConvention=CallingConvention.Cdecl,
             CharSet=CharSet.Ansi)]
  static extern IntPtr complexFunction(
    string format,
    int arg1, int arg2);

  [DllImport("your.dll", CallingConvention=CallingConvention.Cdecl)]
  static extern void free(IntPtr p);

  public static void Main() {
    IntPtr pResult = complexFunction("%d > %s", 2, 1);
    string sResult = Marshal.PtrToStringAnsi(pResult);
    free(pResult);
    Console.WriteLine("result: {0}", sResult);
  }
}