Save a c# array to disk

This article is using dumpmem command to save a C# byte array to a file, while debugging the program and without writing any code to save the data.

Sample C# code 

// See https://aka.ms/new-console-template for more information
var bytes = new byte[1024];
for (int i = 0; i < bytes.Length; i++)
    bytes[i] = (byte)i;

Console.WriteLine(bytes);
Steps to dump bytes contents to disk:
  1. Start debugging the program.
  2. Place a breakpoint at a carefully select point in code, where our data is available (on Console.WriteLine(bytes)).
  3. Go to VSDebugPro menu and open Console.
dumpmem bytes.bin &bytes[0] 1024

The dumpmem utility uses the Visual Studio debugger interface to evaluate the address of &bytes[0]

The hexdump command (very similar to dumpmem) can be used to dump bytes in hex format in a text file

hexdump bytes.txt &bytes[0] 1024 256 256

bytes.txt

2096F50D2E0  00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16
2096F50D3E0  00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16
2096F50D4E0  00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16
2096F50D5E0  00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16
Usage Notes
  • C# objects are stored on the managed heap, which is managed by the .NET runtime.

  • The memory layout of an object includes its header, type information, and the values of its fields. Ex: The bytes array in the example has the following view in the memory window:

    The first 16 bytes are the header.
    bytes (0x000002096F50D2D0)
    Data starts at offset 16.
    &bytes[0] (0x000002096f50d2e0)

  • Every object in C# has a header, which is not visible to the programmer.
  • For reference types (classes), the object’s memory contains the header and instance fields, while the reference itself is a pointer to this memory.
  • Object Size Estimation: Estimating the object size can be tricky, especially for complex objects with nested structures.
  • For value types (structs), when used as fields in a class, their data is embedded directly in the containing object’s memory.
  • Memory Layout Changes: The memory layout of C# objects can change between .NET versions or even between runs of your program.