How Can I Determine the Size of a C# Object Instance in Bytes?

Measuring the Memory Footprint of C# Objects

Precisely determining the memory usage of a C# object instance is crucial for performance tuning and effective memory management. Although C# lacks a direct built-in function for this, we can leverage undocumented internal mechanisms.

Utilizing CLR Internal Data

MSDN Magazine's exploration of CLR internals reveals a hidden field, "Basic Instance Size," within the TypeHandle structure. This field stores the object's instance data size.

Employing RuntimeTypeHandle and Reflection

We can access this field using reflection to obtain the object's TypeHandle. The following code illustrates how to retrieve the instance size:

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

Important Caveats:

This method relies on internal CLR implementation details. Its reliability is not guaranteed across all scenarios or future .NET versions. Furthermore, field offsets and data types might vary across different platforms.

Further Points to Note:

For arrays and strings, the base instance size only reflects the size of the reference to the actual data. To calculate the total memory usage, the size of the elements within the array or string must be added.

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