C#调用WIN32API系列一列举可用COM端口

 C#通过调用WIN32API可以实现非常强大的功能，本文将着重讲述如何通过调用WIN32API实现列举

所有COM端口。
 首先我们看看EnumPorts函数的定义
BOOL EnumPorts(
  LPTSTR pName,       // server name
  DWORD Level,        // information level
  LPBYTE pPorts,      // port information buffer
  DWORD cbBuf,        // size of port information buffer
  LPDWORD pcbNeeded,  // bytes received or required
  LPDWORD pcReturned  // number of ports received
);
 这个api返回信息放在pPorts所指的缓冲区中，是一个
  struct PORT_INFO_1
  {
   string pName;
  }
的结构数组。根据Level参数不同，这个结构数组有些不同。
C#要调用API首先要引入动态库，EnumPorts在winspool.drv这个动态库中。引入语句如下
[DllImport("winspool.drv", CharSet=CharSet.Auto)]
然后是定义PORT_INFO_1结构
  struct PORT_INFO_1
  {
   [MarshalAs(UnmanagedType.LPTStr)]
   public string pName;
  }
 好了，全部的源代码如下：
using System;
using System.Collections;
using System.Runtime.InteropServices;
using System.Diagnostics;
namespace rooksoft.Demo {
 public class EnumPortDemo {
  [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
   struct PORT_INFO_1
  {
   [MarshalAs(UnmanagedType.LPTStr)]
   public string pName;
  }
       
  [DllImport("winspool.drv", CharSet=CharSet.Auto)]
  static extern bool EnumPorts(string pName, int level, IntPtr bufptr,
   int cbBuf, out int pcbNeeded, out int pcReturned);

  public EnumPortDemo()
  {
  }
  public void ListPorts()//out ArrayList portslist
  {
   int pcReturned = 0;
   int pcbNeeded = 0;
   IntPtr outb = IntPtr.Zero;
     
   EnumPorts(null, 1, outb, 0, out pcbNeeded, out pcReturned);
   outb = Marshal.AllocHGlobal(pcbNeeded+1);
   EnumPorts(null, 1, outb, pcbNeeded, out pcbNeeded, out pcReturned);
   PORT_INFO_1[] portsArray = new PORT_INFO_1[pcReturned];

   IntPtr current = outb;
   for (int i=0; i<pcReturned; i++)
   {
    portsArray[i] = (PORT_INFO_1)

Marshal.PtrToStructure(current,
     typeof(PORT_INFO_1));
    current=(IntPtr)

((int)current+Marshal.SizeOf(typeof(PORT_INFO_1)));
    Console.WriteLine(portsArray[i].pName);
   }
   Marshal.FreeHGlobal(outb);
   //return manyArr;
  }
  public static void Main() {
   EnumPortDemo demo = new EnumPortDemo();
   demo.ListPorts();
  }

 }
}
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