IL stsfld Instruction

What is the stsfld instruction in the .NET Framework intermediate language? This instruction stores the value on top of the evaluation stack into a static field, as we demonstrate through this example program.

This .NET IL example shows the stsfld instruction. It provides the source C# program.

Example

So, let's get started with this example C# program. We assign the static field _a in the Program type to the value 3. In the intermediate language, we load a constant value 3 (ldc.i4.3) onto the top of the evaluation stack. Then, we have a stsfld with the argument being the address of the field _a. So the top value (3) is stored into the location pointed to by _a.

Program that has stsfld instruction [C#]

using System;

class Program
{
    static int _a;
    static void Main()
    {
	Program._a = 3;
	if (Program._a == 4)
	{
	    Console.WriteLine(true);
	}
    }
}

IL

.method private hidebysig static void  Main() cil managed
{
  .entrypoint
  // Code size       21 (0x15)
  .maxstack  8
  IL_0000:  ldc.i4.3
  IL_0001:  stsfld     int32 Program::_a
  IL_0006:  ldsfld     int32 Program::_a
  IL_000b:  ldc.i4.4
  IL_000c:  bne.un.s   IL_0014
  IL_000e:  ldc.i4.1
  IL_000f:  call       void [mscorlib]System.Console::WriteLine(bool)
  IL_0014:  ret
} // end of method Program::Main

Notes

What interesting things can we learn about static versus instance fields this way? I have found that static fields are somewhat faster to use than instance fields; for performance, then, you can try to use mostly static fields. Also, avoiding stsfld instructions is probably the best tip: if you can do most computations in local variables, you can get even better performance. Stsfld is, unfortunately, a bit of a slowdown.

Summary

We looked at the stsfld instruction in the intermediate language. This instruction is used for static fields in the C# language and Shared fields in the VB.NET language. It is common and therefore useful to know something about. Micro-optimizations are not usually useful though.