From an old topic: https://forum.tuts4you.com/topic/42934-c-dnlib-how-do-i-change-const-string/?tab=comments#comment-208456

Source Code Stub file:

namespace DlibStub
{
    using System;

    public static class ConstTester
    {
        public const string MYCONST = "1111";
        public const string DNTEST = "2222";

        public static void GetResult()
        { 
            Console.WriteLine($"Result: {MYCONST}");
            Console.WriteLine($"Result: {DNTEST}");
        }
    }
}

IL Code:

field: System.String DlibStub.ConstTester::DNTEST
field: System.String DlibStub.ConstTester::MYCONST
Instruction: IL_0000: ldstr "Dnlib Tester"
Instruction: IL_0000: ldstr "Result: 1111"
Instruction: IL_0005: call System.Void System.Console::set_Title(System.String)
Instruction: IL_0005: call System.Void System.Console::WriteLine(System.String)
Instruction: IL_000A: call System.Void DlibStub.ConstTester::GetResult()
Instruction: IL_000A: ldstr "Result: 2222"
Instruction: IL_000F: call System.String System.Console::ReadLine()
Instruction: IL_000F: call System.Void System.Console::WriteLine(System.String)
Instruction: IL_0014: pop
Instruction: IL_0014: ret
Instruction: IL_0015: ret

Code to replace text:

public static void Inizialize(string fileModule)
{
  using var module = ModuleDefMD.Load(fileModule);
  using var text = File.AppendText("LogDnlib.txt"); // For write to txt
  foreach (TypeDef type in module.GetTypes())
  {
     foreach (FieldDef field in type.Fields)
     {
       text.WriteLine($"Field: {field}");
       text.WriteLine($"FieldName: {field.Name}");
       text.WriteLine($"Field: {field}");

       if (field.HasConstant && field.ElementType.Equals(ElementType.String))
       {
          if (field.Name.String.Contains("MYCONST")) // Find a text named MYCONST
          {
              field.Constant.Value = "test1";
          }
          if (field.Name.String.Contains("DNTEST")) // Find a text named DNTEST
          {
               field.Constant.Value = "test2";
          }
       }            
      }
    }
   module.Write("Patched.exe");
 }

Result (ScreenShots): 

How fix?

 

Edited June 29, 20214 yr by r3xq1

Hey, When you compile the program the Compiler it self replace those "Constants" to their value on method body because its Constant values  so you can't really do that on dnlib.

Edited June 30, 20214 yr by CursedLand

[Update]

I tried replacing both Fields and Ldstr and it worked.

 

foreach (MethodDef method in type.Methods)
{
   if (method.HasBody == false) continue;
   if (method.Body.HasInstructions)
   {
      for (int i = 0; i < method.Body.Instructions.Count; i++)
      {
         if (method.Body.Instructions[i].OpCode == OpCodes.Ldstr && method.Body.Instructions[i].Operand.ToString().Contains("1111"))
         {
             method.Body.Instructions[i].Operand = "test1"; 
         }
         if (method.Body.Instructions[i].OpCode == OpCodes.Ldstr && method.Body.Instructions[i].Operand.ToString().Contains("2222"))
         {
             method.Body.Instructions[i].Operand = "test2";
         } 
         method.Body.SimplifyBranches();
         method.Body.OptimizeMacros();
      }
   }
}