Call function by pointer in C#

Call function by pointer in C#

I trying to call a function of an other process by pointer in C# but
unfortunately i don't find the answer for it.
In C++ i can do this:
#define DefinedMemoryAddress 0x123456
struct someStruct
{
int someInt;
float someFloat;
}
int main()
{
someStruct createdStruct = ...;
( (void (_stdcall*)(someStruct*)) DefinedMemoryAddress)( createdStruct );
}
Somebody can help me with a C# version of it?