How Can I Estimate the Byte Size of C# Objects?

C# object instance byte size estimation

Question:

Determining the size of any object instance (including collections, combinations, and individual objects) is a common task when managing object size.

Solution:

While there is no official method, you can leverage reflection and undocumented .NET internals to estimate object size:

object obj = new List<int>();
RuntimeTypeHandle th = obj.GetType().TypeHandle;
int size = *(*(int**) &th + 1);
Console.WriteLine(size);

Explanation:

• RuntimeTypeHandle Provides access to the internal representation of a type.
• Through pointer operations, you can retrieve the Base Instance Size field to estimate the object size.
• For collections and complex objects, you may need to recursively estimate the size of the containing elements.

Limitations:

• This method relies on undocumented internal mechanisms and may be affected by future .NET updates.
• It may not accurately reflect object sizes for all types (such as arrays, strings, or StringBuilder).
• It provides estimates only; actual memory usage may vary.

Extension methods:

For convenience, you may consider implementing an extension method on the Object class to simplify size retrieval:

public static int GetEstimatedByteSize(this object obj)
{
    RuntimeTypeHandle th = obj.GetType().TypeHandle;
    return *(*(int**) &th + 1);
}

Please note that this extension method should be used with caution and is not guaranteed to be accurate for all types and scenarios.

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