Access violation reading location 0x00000000 when calling managed code from unmanaged code

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Hi, I have developed a c# dll that makes http reqest using System.Net namespace. If I call the dll methods from an c# programm everything workes fine but i need to use this dll from native c++ code. For this i used COM interop service. All goes fine until is called GetResponseAsync() function. At this poin the program crashes and return Access violation reading location 0x00000000.

C#

  public async Task PostRequest(string URL, string jsonRequestStr, string accessToken)
  {
          HttpWebRequest httpPostRequest = (HttpWebRequest)WebRequest.Create(URL);
          httpPostRequest.Method = "POST";
          if (accessToken != "")
          {
              httpPostRequest.Headers.Add(string.Format("Authorization: Bearer {0}", accessToken));
          }

          byte[] requestBuffer = Encoding.UTF8.GetBytes(jsonRequestStr);
          httpPostRequest.ContentLength = requestBuffer.Length;
          httpPostRequest.ContentType = "application/json";

          using (var requestStream = new StreamWriter(httpPostRequest.GetRequestStream()))
          {
              await requestStream.WriteAsync(jsonRequestStr);
          }

          WebResponse tokenResponse = httpPostRequest.GetResponse();
          using (StreamReader reader = new StreamReader(tokenResponse.GetResponseStream()))
          {
              string responseText = await reader.ReadToEndAsync();

              if (responseText != "")
              {
                  this.jResponseDecoded = JObject.Parse(responseText);
              }

          }
}

What I have tried:

I have tried to make Http request with HttpClient but also crashed.

Posted 3-Mar-21 21:56pm

Member 14649480

Updated 3-Mar-21 22:37pm

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OriginalGriff · Answer 1 · 2021-03-03T22:37:00

Firstly,you aren't calling GetResponseAsync in that code.
Secondly, half the other stuff we have no idea what exactly they are: JObject, what is returned by your GetResponse call.
Thirdly, why are you preparing a byte array version of your string, and then not using it? You send the Unicode String instead, which may be part of your problem - it's not necessarily the same size as the buffer you told it you were using.

And we can't find out any of that stuff!
So, it's going to be up to you.
Fortunately, you have a tool available to you which will help you find out what is going on: the debugger. If you don't know how to use it then a quick Google for "Visual Studio debugger" should give you the info you need.

Put a breakpoint on the first line in the function, and run your code through the debugger. Then look at your code, and at your data and work out what should happen manually. Then single step each line checking that what you expected to happen is exactly what did. When it isn't, that's when you have a problem, and you can back-track (or run it again and look more closely) to find out why.

Sorry, but we can't do that for you - time for you to learn a new (and very, very useful) skill: debugging!