Marshal
Learn managed/unmanaged conversion with the Marshal class.
The Marshal class
The System.Runtime.InteropServices.Marshal class performs manual conversion between managed and unmanaged types. For example Marshal.StringToHGlobalAnsi(str) copies a string into native memory; Marshal.FreeHGlobal(ptr) releases it.
This manual marshaling is used for special types that DllImport does not convert automatically. Because you manage memory by hand, calling FreeHGlobal is critical; otherwise a memory leak occurs.
Blittable types
Blittable types have the same memory layout on the managed and unmanaged side; no marshal copy is needed (e.g. int, byte, IntPtr).
Non-blittable types (string, bool, char) require conversion. So when working with native APIs, preferring blittable types improves performance and reduces conversion cost.
Exercise Copy a string with Marshal
In Main copy a string into native memory with IntPtr ptr = Marshal.StringToHGlobalAnsi("Hello");. Print Console.WriteLine("Copied");. Finally release it with Marshal.FreeHGlobal(ptr);.
Show example solution
IntPtr ptr = Marshal.StringToHGlobalAnsi("Hello"); Console.WriteLine("Copied"); Marshal.FreeHGlobal(ptr);
Example solution:
using System;
using System.Runtime.InteropServices;
class Program
{
static void Main()
{
IntPtr ptr = Marshal.StringToHGlobalAnsi("Hello");
Console.WriteLine("Copied");
Marshal.FreeHGlobal(ptr);
}
}Test yourself
-
Copy a string into native memory
IntPtr ptr = Marshal.____("merhaba");Show answer
IntPtr ptr = Marshal.StringToHGlobalAnsi("merhaba"); -
Which is not a blittable type?
- int
- string
- byte
- IntPtr
Show answer
string — Correct. string is not blittable; it needs marshaling.
-
Match the Marshal methods
- Marshal.StringToHGlobalAnsi
- String → native memory
- Marshal.FreeHGlobal
- Free native memory
- Marshal.ReadInt32
- Read int from native address
- Marshal.Copy
- Array copy