P/Invoke

1.P/Invoke是什么？有何作用？

2.简单的使用P/Invoke的demo

1.P/Invoke是什么？有何作用？

P/Invoke使得C#程序调用非托管的成为可能，例如可以使用P/Invoke来调用win32 api。

2.简单的使用P/Invoke的demo

2.1 使用P/Invoke直接调用win32 api

public class Program
    {
        /// <summary>
        /// import kernel32.dll
        /// </summary>
        /// <param name="source"></param>
        /// <param name="dest"></param>
        /// <returns></returns>
        [DllImport("kernel32.dll", EntryPoint = "MoveFile",
            ExactSpelling = false,
            CharSet = CharSet.Unicode,
            SetLastError = true)]
        static extern bool MoveFile(string source, string dest);

        static void Main(string[] args)
        {
            // Call P/Invoke
            string source = @"d:\test.txt";
            string dest = @"d:\test.txt.bak";
            if (UsingPInvoke.Program.MoveFile(source, dest) == true)
            {
                Console.WriteLine("Move File Ok!");
            }
            else
            {
                Console.WriteLine("Move File Error!");
            }
        }

}

2.2 C#中的指针

public class UsingPointers
    {
        const uint GenericRead = 0x80000000;
        const uint OpenExisting = 3;
        const uint UseDefault = 0;
        int fileHandle;
        [DllImport("kernel32.dll",
            SetLastError = true)]
        static extern unsafe int CreateFile(
            string filename,
            uint desiredAccess,
            uint shareMode,
            uint attributes,
            uint createDisposition,
            uint flagsAndAttributes,
            uint templateFile
        );
        [DllImport("kernel32.dll",
            SetLastError = true)]
        static extern unsafe bool ReadFile(
            int hFile,
            void* lpBuffer,
            int bBytesToRead,
            int* nBytesRead,
            int overlapped
        );
        public UsingPointers(string filename)
        {
            this.fileHandle = CreateFile(
                filename,
                GenericRead,
                UseDefault,
                UseDefault,
                OpenExisting,
                UseDefault,
                UseDefault
            );
        }
        public unsafe int Read(byte[] buffer, int index, int count)
        {
            int byteRead = 0;
            // 将byte[]转换成byte*
            fixed(byte* bytePointer = buffer)
            {
                // 调用win32函数
                ReadFile(
                    fileHandle,
                    bytePointer + index,
                    count,
                    &byteRead,
                    0
                    );
            }
            return byteRead;
        }
    }

注意编译时，需要更改项目属性：