IntPtr.ToPointer Method

Definition

Namespace:

System

Assembly:

System.Runtime.dll

Source:

IntPtr.cs

Important

This API is not CLS-compliant.

Converts the value of this instance to a pointer to an unspecified type.

public:
 void* ToPointer();

[System.CLSCompliant(false)]
public void* ToPointer ();

[<System.CLSCompliant(false)>]
member this.ToPointer : unit -> nativeptr<unit>

Returns

Void*

A pointer to Void; that is, a pointer to memory containing data of an unspecified type.

Attributes

CLSCompliantAttribute

Examples

The following example uses managed pointers to reverse the characters in an array. After it initializes a String object and gets its length, it does the following:

• Calls the Marshal.StringToHGlobalAnsi method to copy the Unicode string to unmanaged memory as ANSI (one-byte) characters. The method returns an IntPtr object that points to the beginning of the unmanaged string.

• Calls the Marshal.AllocHGlobal method to allocate the same number of bytes as the unmanaged string occupies. The method returns an IntPtr object that points to the beginning of the unmanaged block of memory.

• Calls the ToPointer method to get an unmanaged pointer to the starting address of the string and the unmanaged block of memory, and adds one less than the length of the string to the starting address of the ANSI string. Because the unmanaged string pointer now points to the end of the string, the copy operation will copy a character from the end of the string to the start of the memory block.

• Uses a loop to copy each character from the string to the unmanaged block of memory. After each copy operation, it decrements the pointer to the address of the next location in the unmanaged ANSI string and increments the pointer to the next address in the unmanaged block.

• Calls the Marshal.PtrToStringAnsi to convert the unmanaged memory block containing the copied ANSI string to a managed Unicode String object.

• After displaying the original and reversed strings, calls the Marshal.FreeHGlobal method to free the memory allocated for the unmanaged ANSI string and the unmanaged block of memory.

using namespace System;
using namespace System::Runtime::InteropServices;

class NotTooSafeStringReverse
{
public:
    static void Main()
    {
        String^ stringA = "I seem to be turned around!";
        int copylen = stringA->Length;

        // Allocate HGlobal memory for source and destination strings
        IntPtr sptr = Marshal::StringToHGlobalAnsi(stringA);
        IntPtr dptr = Marshal::AllocHGlobal(copylen + 1);

        char *src = (char *)sptr.ToPointer();
        char *dst = (char *)dptr.ToPointer();

        if (copylen > 0)
        {
            // set the source pointer to the end of the string
            // to do a reverse copy.
            src += copylen - 1;

            while (copylen-- > 0)
            {
                *dst++ = *src--;
            }
            *dst = 0;
        }
        String^ stringB = Marshal::PtrToStringAnsi(dptr);

        Console::WriteLine("Original:\n{0}\n", stringA);
        Console::WriteLine("Reversed:\n{0}", stringB);

        // Free HGlobal memory
        Marshal::FreeHGlobal(dptr);
        Marshal::FreeHGlobal(sptr);
    }
};

int main()
{
    NotTooSafeStringReverse::Main();
}

// The progam has the following output:
//
// Original:
// I seem to be turned around!
//
// Reversed:
// !dnuora denrut eb ot mees I

using System;
using System.Runtime.InteropServices;

class NotTooSafeStringReverse
{
    static public void Main()
    {
        string stringA = "I seem to be turned around!";
        int copylen = stringA.Length;

        // Allocate HGlobal memory for source and destination strings
        IntPtr sptr = Marshal.StringToHGlobalAnsi(stringA);
        IntPtr dptr = Marshal.AllocHGlobal(copylen + 1);

        // The unsafe section where byte pointers are used.
        unsafe
        {
            byte *src = (byte *)sptr.ToPointer();
            byte *dst = (byte *)dptr.ToPointer();

            if (copylen > 0)
            {
                // set the source pointer to the end of the string
                // to do a reverse copy.
                src += copylen - 1;

                while (copylen-- > 0)
                {
                    *dst++ = *src--;
                }
                *dst = 0;
            }
        }
        string stringB = Marshal.PtrToStringAnsi(dptr);

        Console.WriteLine("Original:\n{0}\n", stringA);
        Console.WriteLine("Reversed:\n{0}", stringB);

        // Free HGlobal memory
        Marshal.FreeHGlobal(dptr);
        Marshal.FreeHGlobal(sptr);
    }
}

// The progam has the following output:
//
// Original:
// I seem to be turned around!
//
// Reversed:
// !dnuora denrut eb ot mees I

#nowarn "9"
open System.Runtime.InteropServices
open FSharp.NativeInterop

[<EntryPoint>]
let main _ =
    let stringA = "I seem to be turned around!"
    let mutable copylen = stringA.Length

    // Allocate HGlobal memory for source and destination strings
    let sptr = Marshal.StringToHGlobalAnsi stringA
    let dptr = Marshal.AllocHGlobal(copylen + 1)

    let mutable src: byte nativeptr = sptr.ToPointer() |> NativePtr.ofVoidPtr
    let mutable dst: byte nativeptr = dptr.ToPointer() |> NativePtr.ofVoidPtr

    if copylen > 0 then
        // set the source pointer to the end of the string
        // to do a reverse copy.
        src <- 
            NativePtr.toNativeInt src + nativeint (copylen - 1) 
            |> NativePtr.ofNativeInt

        while copylen > 0 do
            copylen <- copylen - 1
            NativePtr.read src |> NativePtr.write dst
            dst <- NativePtr.toNativeInt dst + 1n |> NativePtr.ofNativeInt
            src <- NativePtr.toNativeInt src - 1n |> NativePtr.ofNativeInt
        NativePtr.write dst 0uy

    let stringB = Marshal.PtrToStringAnsi dptr

    printfn $"Original:\n{stringA}\n"
    printfn $"Reversed:\n{stringB}"

    // Free HGlobal memory
    Marshal.FreeHGlobal dptr
    Marshal.FreeHGlobal sptr
    0

// The progam has the following output:
//
// Original:
// I seem to be turned around!
//
// Reversed:
// !dnuora denrut eb ot mees I