Find out dependencies of all DLLs?

I have a collection of DLLs(say 20). How do I find out all the DLLs on which one specific DLL (say DLL A) is depending upon?

If you mean programmatically, use Assembly.GetReferencedAssemblies.

You can use that recursively to find all the assemblies you need. (So you find the dependencies of X, then the dependencies of the dependencies, etc.)

Since the question is tagged "C#", I would assume you are talking about managed dlls (assemblies). In that case, dependencywalker is not useful. If you want to do that with a program, good ones are dotPeek by JetBrians and Reflector by RedGate. Or you can even use the object inspector in Visual Studio.

However, it can be a long process and cumbersome too. I would write a short C# program/F# script that uses Assembly.GetReferencedAssemblies, as Jon mentioned.

If instead you want to examine native DLLs dependencies with a program (C# code), you have to walk the examine the PE file (the MS dll and exe file format) and its IAT (import address table). Not easy, but not impossible...

I would start here on MSDN and here to understand PE sections, and use a managed library to read it (there are many, including some from the Mono project (I'm thinking of Cecil, it should work with native binaries too); in the past I have used this one from the good John Gough.

You can use dependency walker http://www.dependencywalker.com to figure this out. Take note on the difference between x32 and x64 though.

> Dependency Walker is a free utility that scans any 32-bit or 64-bit > Windows module (exe, dll, ocx, sys, etc.) and builds a hierarchical > tree diagram of all dependent modules.

All answer credit goes to previous authors for the usage of Assembly.GetReferencedAssemblies. This is just a write-and-forget C# console app that works solely for .NET assemblies. return 0 on assemblies you were able to check, and when successful, outputs them to STDOUT. Everything else will return 1 and print some kind of error output. You can grab the gist here.

using System;
using System.Reflection;
using System.IO;
namespace DotNetInspectorGadget
{
    class DotNetInspectorGadget 
    {
        static int Main(string[] args) 
        {
          if(args.GetLength(0) < 1)
          {
            Console.WriteLine("Add a single parameter that is your" +
            " path to the file you want inspected.");
            return 1;
          }
          try {
                var assemblies = Assembly.LoadFile(@args[0]).GetReferencedAssemblies();
                
                if (assemblies.GetLength(0) > 0)
                {
                  foreach (var assembly in assemblies)
                  {
                    Console.WriteLine(assembly);
                  }
                  return 0;
                }
          }
          catch(Exception e) {
            Console.WriteLine("An exception occurred: {0}", e.Message);
            return 1;
          } finally{}
          
            return 1;
        }
    }
}

Usage:

call %cd%\dotnet_inspector_gadget.exe C:\Windows\Microsoft.NET\assembly\GAC_64\Microsoft.ConfigCI.Commands\v4.0_10.0.0.0__31bf3856ad364e35\Microsoft.ConfigCI.Commands.dll

Output:

> mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 > System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 > System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 > System.Management.Automation, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35 > System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 > System.Security, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a > System.Management, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a

For .NET assemblies, a terrific tool to view the assemblies an assembly is dependent on is AsmSpy.

If you want the DLL's (the files) then, Assembly.GetReferencedAssemblies will also return the .Net Framework assemblies.

Here is a simple code snippet that will get the dll's it can find in the current directory (and also include some other related files):

private readonly string[] _extensions = { ".dll", ".exe", ".pdb", ".dll.config", ".exe.config" };

private string[] GetDependentFiles(Assembly assembly)
{
    AssemblyName[] asm = assembly.GetReferencedAssemblies();
    List<string> paths = new List<string>(asm.Length);
    for (int t = asm.Length - 1; t >= 0; t--)
    {
        for (int e = _extensions.Length - 1; e >= 0; e--)
        {
            string path = Path.GetFullPath(asm[t].Name + _extensions[e]);
            if (File.Exists(path)) paths.Add(path);
        }
    }

    return paths.ToArray();
}

You can call it like so: MessageBox.Show(string.Join("\r\n", GetDependentFiles(Assembly.GetEntryAssembly())));