Migrate snippets to samples repo (#897)

Author: nxtn

snippets/standard/interop/pinvoke/enumwindows.cs

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+using System;
+using System.Runtime.InteropServices;
+
+namespace ConsoleApplication1
+{
+    public static class Program
+    {
+        // Define a delegate that corresponds to the unmanaged function.
+        private delegate bool EnumWC(IntPtr hwnd, IntPtr lParam);
+
+        // Import user32.dll (containing the function we need) and define
+        // the method corresponding to the native function.
+        [DllImport("user32.dll")]
+        private static extern int EnumWindows(EnumWC lpEnumFunc, IntPtr lParam);
+
+        // Define the implementation of the delegate; here, we simply output the window handle.
+        private static bool OutputWindow(IntPtr hwnd, IntPtr lParam)
+        {
+            Console.WriteLine(hwnd.ToInt64());
+            return true;
+        }
+
+        public static void Main(string[] args)
+        {
+            // Invoke the method; note the delegate as a first parameter.
+            EnumWindows(OutputWindow, IntPtr.Zero);
+        }
+    }
+}

snippets/standard/interop/pinvoke/ftw-linux.cs

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+using System;
+using System.Runtime.InteropServices;
+
+namespace PInvokeSamples
+{
+    public static class Program
+    {
+        // Define a delegate that has the same signature as the native function.
+        private delegate int DirClbk(string fName, StatClass stat, int typeFlag);
+
+        // Import the libc and define the method to represent the native function.
+        [DllImport("libc.so.6")]
+        private static extern int ftw(string dirpath, DirClbk cl, int descriptors);
+
+        // Implement the above DirClbk delegate;
+        // this one just prints out the filename that is passed to it.
+        private static int DisplayEntry(string fName, StatClass stat, int typeFlag)
+        {
+            Console.WriteLine(fName);
+            return 0;
+        }
+
+        public static void Main(string[] args)
+        {
+            // Call the native function.
+            // Note the second parameter which represents the delegate (callback).
+            ftw(".", DisplayEntry, 10);
+        }
+    }
+
+    // The native callback takes a pointer to a struct. The below class
+    // represents that struct in managed code. You can find more information
+    // about this in the section on marshalling below.
+    [StructLayout(LayoutKind.Sequential)]
+    public class StatClass
+    {
+        public uint DeviceID;
+        public uint InodeNumber;
+        public uint Mode;
+        public uint HardLinks;
+        public uint UserID;
+        public uint GroupID;
+        public uint SpecialDeviceID;
+        public ulong Size;
+        public ulong BlockSize;
+        public uint Blocks;
+        public long TimeLastAccess;
+        public long TimeLastModification;
+        public long TimeLastStatusChange;
+    }
+}

snippets/standard/interop/pinvoke/ftw-macos.cs

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+using System;
+using System.Runtime.InteropServices;
+
+namespace PInvokeSamples
+{
+    public static class Program
+    {
+        // Define a delegate that has the same signature as the native function.
+        private delegate int DirClbk(string fName, StatClass stat, int typeFlag);
+
+        // Import the libc and define the method to represent the native function.
+        [DllImport("libSystem.dylib")]
+        private static extern int ftw(string dirpath, DirClbk cl, int descriptors);
+
+        // Implement the above DirClbk delegate;
+        // this one just prints out the filename that is passed to it.
+        private static int DisplayEntry(string fName, StatClass stat, int typeFlag)
+        {
+            Console.WriteLine(fName);
+            return 0;
+        }
+
+        public static void Main(string[] args)
+        {
+            // Call the native function.
+            // Note the second parameter which represents the delegate (callback).
+            ftw(".", DisplayEntry, 10);
+        }
+    }
+
+    // The native callback takes a pointer to a struct. The below class
+    // represents that struct in managed code.
+    [StructLayout(LayoutKind.Sequential)]
+    public class StatClass
+    {
+        public uint DeviceID;
+        public uint InodeNumber;
+        public uint Mode;
+        public uint HardLinks;
+        public uint UserID;
+        public uint GroupID;
+        public uint SpecialDeviceID;
+        public ulong Size;
+        public ulong BlockSize;
+        public uint Blocks;
+        public long TimeLastAccess;
+        public long TimeLastModification;
+        public long TimeLastStatusChange;
+    }
+}

snippets/standard/interop/pinvoke/getpid-linux.cs

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+using System;
+using System.Runtime.InteropServices;
+
+namespace PInvokeSamples
+{
+    public static class Program
+    {
+        // Import the libc shared library and define the method
+        // corresponding to the native function.
+        [DllImport("libc.so.6")]
+        private static extern int getpid();
+
+        public static void Main(string[] args)
+        {
+            // Invoke the function and get the process ID.
+            int pid = getpid();
+            Console.WriteLine(pid);
+        }
+    }
+}

snippets/standard/interop/pinvoke/getpid-macos.cs

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+using System;
+using System.Runtime.InteropServices;
+
+namespace PInvokeSamples
+{
+    public static class Program
+    {
+        // Import the libSystem shared library and define the method
+        // corresponding to the native function.
+        [DllImport("libSystem.dylib")]
+        private static extern int getpid();
+
+        public static void Main(string[] args)
+        {
+            // Invoke the function and get the process ID.
+            int pid = getpid();
+            Console.WriteLine(pid);
+        }
+    }
+}

snippets/standard/interop/pinvoke/messagebox.cs

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+using System;
+using System.Runtime.InteropServices;
+
+public class Program
+{
+    // Import user32.dll (containing the function we need) and define
+    // the method corresponding to the native function.
+    [DllImport("user32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
+    private static extern int MessageBox(IntPtr hWnd, string lpText, string lpCaption, uint uType);
+
+    public static void Main(string[] args)
+    {
+        // Invoke the function as a regular managed method.
+        MessageBox(IntPtr.Zero, "Command-line message box", "Attention!", 0);
+    }
+}