How would one access object properties in CIL (MSIL)?

Question

I'm an absolute beginner, you see. Say I have a string object on the stack and want to get the number of characters in it - its .Length property. How would I get the int32 number hidden inside?

Many thanks in advance!

Answer 1

There's really no such thing as properties in IL. There are only fields and methods. The C# property construct is translated to get_PropertyName and set_PropertyName methods by the compiler, so you have to call these methods to access the property.

Sample (debug) IL for code

var s = "hello world";
var i = s.Length;

IL

  .locals init ([0] string s,
           [1] int32 i)
  IL_0000:  nop
  IL_0001:  ldstr      "hello world"
  IL_0006:  stloc.0
  IL_0007:  ldloc.0
  IL_0008:  callvirt   instance int32 [mscorlib]System.String::get_Length()
  IL_000d:  stloc.1

As you can see the Length property is accessed via the call to get_Length.

Answer 2

I cheated ... I took the following C# code and took a look at it in ildasm/Reflector

static void Main(string[] args)
{
    string h = "hello world";
    int i = h.Length;
}

is equivalent to

.method private hidebysig static void Main(string[] args) cil managed
{
    .entrypoint
    .maxstack 1
    .locals init (
        [0] string h,
        [1] int32 i)
    L_0000: nop 
    L_0001: ldstr "hello world"
    L_0006: stloc.0 
    L_0007: ldloc.0 
    L_0008: callvirt instance int32 [mscorlib]System.String::get_Length()
    L_000d: stloc.1 
    L_000e: ret 
}