C#调用API示例

摘自MSDN，这是一段C#调用Windows系统API函数的示例代码。
在自定义的FileReader类中，导入了CreateFile, ReadFile, CloseHandle三个API函数，并新建了Open，Read，Close方法来应用它们。
在编译时需用unsafe选项，因为用到了C#中所谓的指针。
FileReader类在窗体程序、控制台程序、Web程序中皆可使用，不过这只是一个示例，个人可自由发挥，使用其他API，来实现某些“高级”功能。

// readfile.cs
// compile with: /unsafe
// arguments: readfile.cs

// Use the program to read and display a text file.
using System;
using System.Runtime.InteropServices;
using System.Text;

class FileReader
{
const uint GENERIC_READ = 0x80000000;
const uint OPEN_EXISTING = 3;
IntPtr handle;

[DllImport("kernel32", SetLastError=true)]
static extern unsafe IntPtr CreateFile(
string FileName, // file name
uint DesiredAccess, // access mode
uint ShareMode, // share mode
uint SecurityAttributes, // Security Attributes
uint CreationDisposition, // how to create
uint FlagsAndAttributes, // file attributes
int hTemplateFile // handle to template file
);

[DllImport("kernel32", SetLastError=true)]
static extern unsafe bool ReadFile(
IntPtr hFile, // handle to file
void* pBuffer, // data buffer
int NumberOfBytesToRead, // number of bytes to read
int* pNumberOfBytesRead, // number of bytes read
int Overlapped // overlapped buffer
);

[DllImport("kernel32", SetLastError=true)]
static extern unsafe bool CloseHandle(
IntPtr hObject // handle to object
);

public bool Open(string FileName)
{
// open the existing file for reading
handle = CreateFile(
FileName,
GENERIC_READ,
0,
0,
OPEN_EXISTING,
0,
0);

if (handle != IntPtr.Zero)
return true;
else
return false;
}

public unsafe int Read(byte[] buffer, int index, int count)
{
int n = 0;
fixed (byte* p = buffer)
{
if (!ReadFile(handle, p + index, count, &n, 0))
return 0;
}
return n;
}

public bool Close()
{
// close file handle
return CloseHandle(handle);
}
}

class Test
{
public static int Main(string[] args)
{
if (args.Length != 1)
{
Console.WriteLine("Usage : ReadFile <FileName>");
return 1;
}

if (! System.IO.File.Exists(args[0]))
{
Console.WriteLine("File " + args[0] + " not found.");
return 1;
}

byte[] buffer = new byte[128];
FileReader fr = new FileReader();

if (fr.Open(args[0]))
{

// Assume that an ASCII file is being read
ASCIIEncoding Encoding = new ASCIIEncoding();

int bytesRead;
do
{
bytesRead = fr.Read(buffer, 0, buffer.Length);
//string content = Encoding.GetString(buffer,0,bytesRead);
string content = System.Text.Encoding.Default.GetString(buffer, 0, bytesRead);
Console.Write("{0}", content);
}
while ( bytesRead > 0);

fr.Close();
return 0;
}
else
{
Console.WriteLine("Failed to open requested file");
return 1;
}
}
}