C#——Marshal.StructureToPtr方法简介

晨曦之光 发布于 2012/03/09 14:14
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Marshal.StructureToPtr方法简介

                                            
                                            

1. 功能及位置

                                            
                                            
将数据从托管对象封送到非托管内存块,属于.NET Framework 类库
命名空间:System.Runtime.InteropServices
程序集:mscorlib(在 mscorlib.dll 中)
                                            
                                            

2. 语法

                                            
                                            
C#:
      [ComVisibleAttribute(true)] public static void StructureToPtr (Object structure,IntPtr ptr,bool fDeleteOld);
C++:
      [ComVisibleAttribute(true)]public: static void StructureToPtr (Object^ structure, IntPtr ptr, bool fDeleteOld);
                                            
                                            

3. 参数说明

                                            
                                            
structure:托管对象,包含要封送的数据。该对象必须是格式化类的实例。
ptr:指向非托管内存块的指针,必须在调用此方法之前分配该指针。
fDeleteOld:设置为 true 可在执行Marshal.DestroyStructure方法前对 ptr 参数调用此方法。请注意,传递 false 可导致内存泄漏。
                                            
                                            

4. 异常

                                            
                                            
异常类型:ArgumentException
条件:structrue参数是泛型类型
                                            
                                            

5. 备注

                                            
                                            
StructureToPtr将结构的内容复制到 ptr 参数指向的预分配内存块。如果 fDeleteOld 参数为 true,则使用嵌入指
针上适当的删除 API 来删除最初由 ptr 指向的缓冲区,但该缓冲区必须包含有效数据。此方法为在镜像托管类中指
定的每个引用字段执行清理工作。
                                            
假设 ptr 指向非托管内存块。此内存块的布局由相应的托管类 structure 描述。StructureToPtr将字段值从结构封
送到指针。假设 ptr 块包含引用字段,该字段指向当前包含“abc”的字符串缓冲区。假设托管端上相应的字段是包含“vwxyz”的字符串。如果不另行通知它,StructureToPtr将分配一个新的非托管缓冲区来保存“vwxyz”,并将它挂钩到 ptr 块。这将丢弃旧缓冲区“abc”使之漂移而不将其释放回非托管堆。最后,您将得到一个孤立的缓冲区,它表示在代码中存在内存泄漏。如果将 fDeleteOld 参数设置为真,则 StructureToPtr 在继续为“vwxyz”分配新缓冲区之前释放保存“abc”的缓冲区。
                                            
                                            

6. 举例

                                            
                                            
定义PERSON结构,并将该结构的一个变量拷贝到非托管内存,再将该内存中的PERSON还原为PERSON对象,观察其内容的变化。
                                            
                                            
源代码如下:
                                            
                                            
using  System;
using  System.Text;
using  System.Runtime.InteropServices;

namespace  testStructureToPtr
{
    
public static class define  //define some constant
    {        
        
public const int MAX_LENGTH_OF_IDENTICARDID = 20;   //maximum length of identicardid
        public const int MAX_LENGTH_OF_NAME = 50;           //maximum length of name
        public const int MAX_LENGTH_OF_COUNTRY = 50;        //maximum length of country
        public const int MAX_LENGTH_OF_NATION = 50;         //maximum length of nation
        public const int MAX_LENGTH_OF_BIRTHDAY = 8;        //maximum length of birthday
        public const int MAX_LENGTH_OF_ADDRESS = 200;       //maximum length of address
    }


    
public struct PERSON    //person structure
    {
        
//MarshalAs:指示如何在托管代码和非托管代码之间封送数据
        
//UnmanagedType:指定如何将参数或字段封送到非托管内存块
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = define.MAX_LENGTH_OF_IDENTICARDID)]
        
public byte[] identicardid;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst 
= define.MAX_LENGTH_OF_NAME)]
        
public byte[] name;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst 
= define.MAX_LENGTH_OF_COUNTRY)]
        
public byte[] country;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst 
= define.MAX_LENGTH_OF_NATION)]
        
public byte[] nation;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst 
= define.MAX_LENGTH_OF_BIRTHDAY)]
        
public byte[] birthday;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst 
= define.MAX_LENGTH_OF_ADDRESS)]
        
public byte[] address;
    }


    
class testProgram
    
{
        
private static byte _fillChar = ;      //the fill character

        
//convert string to byte array in Ascii with length is len        
        public static byte[] CodeBytes(string str, int len)
        
{
            
if (string.IsNullOrEmpty(str))
            
{
                str 
= string.Empty;
            }

 
            
byte[] result = new byte[len];
            
byte[] strBytes = Encoding.Default.GetBytes(str);

            
//copy the array converted into result, and fill the remaining bytes with 0
            for (int i = ; i < len; i++)
                result[i] 
= ((i < strBytes.Length) ? strBytes[i] : _fillChar);
            
            
return result;
        }


        
//show the person information
        public static void ShowPerson(PERSON person)
        
{
            Console.WriteLine(
"cardid   :" + Encoding.ASCII.GetString(person.identicardid));
            Console.WriteLine(
"name     :" + Encoding.ASCII.GetString(person.name));
            Console.WriteLine(
"country  :" + Encoding.ASCII.GetString(person.country));
            Console.WriteLine(
"nation   :" + Encoding.ASCII.GetString(person.nation));
            Console.WriteLine(
"birthday :" + Encoding.ASCII.GetString(person.birthday));
            Console.WriteLine(
"address  :" + Encoding.ASCII.GetString(person.address));
        }


        
static void Main(string[] args)
        
{
            PERSON person;
            person.identicardid 
= CodeBytes("123456198001011111", define.MAX_LENGTH_OF_IDENTICARDID);
            person.name 
= CodeBytes("jackson", define.MAX_LENGTH_OF_NAME);
            person.country 
= CodeBytes("China", define.MAX_LENGTH_OF_COUNTRY);
            person.nation 
= CodeBytes("HanZu", define.MAX_LENGTH_OF_NATION);
            person.birthday 
= CodeBytes("19800101", define.MAX_LENGTH_OF_BIRTHDAY);
            person.address 
= CodeBytes("Luoshan Road, Shanghai", define.MAX_LENGTH_OF_ADDRESS);

            
int nSizeOfPerson = Marshal.SizeOf(person);
            IntPtr intPtr 
= Marshal.AllocHGlobal(nSizeOfPerson);
            
            Console.WriteLine(
"The person infomation is as follows:");
            ShowPerson(person);

            
try
            
{
                
//将数据从托管对象封送到非托管内存块,该内存块开始地址为intPtr
                Marshal.StructureToPtr(person, intPtr, true);

                
//将数据从非托管内存块封送到新分配的指定类型的托管对象anotherPerson
                PERSON anotherPerson = (PERSON)Marshal.PtrToStructure(intPtr, typeof(PERSON));

                Console.WriteLine(
"The person after copied is as follows:");
                ShowPerson(anotherPerson);
            }

            
catch (ArgumentException)
            
{
                
throw;
            }

            
finally
            
{
                Marshal.FreeHGlobal(intPtr);    
//free tha memory
            }

        }

    }

}
                                            
                                            
运行过程中的对象地址及其内容如下:
                                            
                                            
intPtr指向的内存块的内容就是程序中对person对象所赋的初值,如下图所示,共计378个字节:
                                            
                                            
                                            
                                            
对象person和another的地址及其identicardid成员的地址:
                                            
                                            
                                            
                                            
对象person的identicardid成员的内容,即程序中的值123456198001011111,最后的2个字节为0,图中显示的是20个元素的ASCII码的16进制数值:
                                            
                                            
                                            
                                            
运行结果如下:
                                            
                                            

原文链接:http://blog.csdn.net/livelylittlefish/article/details/2423764
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