Throwing exceptions from a constructor in .NET

Question

Are there any memory leaks when I throw an exception from a constructor like the following?

class Victim
{
    public string var1 = "asldslkjdlsakjdlksajdlksadlksajdlj";

    public Victim()
    {
        //throw new Exception("oops!");
    }
}

Will the failing objects be collected by the garbage collector?

Answer 1

In general this is safe from the perspective of not leaking memory. But throwing exceptions from a constructor is dangerous if you allocate unmanaged resources in the type. Take the following example

public class Foo : IDisposable { 
  private IntPtr m_ptr;
  public Foo() {
    m_ptr = Marshal.AllocHGlobal(42);
    throw new Exception();
  }
  // Most of Idisposable implementation ommitted for brevity
  public void Dispose() {
    Marshal.FreeHGlobal(m_ptr);
  }
}

This class will leak memory every time you try to create even if you use a using block. For instance, this leaks memory.

using ( var f = new Foo() ) {
  // Won't execute and Foo.Dispose is not called
} 

Answer 2

Throwing exceptions from a constructor should be fine if you have created no unmanaged resources. However, if you do create unmanaged resources in the constructor, the whole body of that constructor, including throws, should be wrapped in a try/catch. To steal JaredPar's great example:

public class Foo : IDisposable { 
  private IntPtr m_ptr;
  public Foo() {
    try
    {
        m_ptr = Marshal.AllocHGlobal(42);
        throw new Exception();
    }
    catch
    {
        Dispose();
        throw;
    }
  }
  // Most of Idisposable implementation ommitted for brevity
  public void Dispose() {
    Marshal.FreeHGlobal(m_ptr);
  }
}

The following would now work:

using ( var f = new Foo() ) {
  // Won't execute, but Foo still cleans itself up
}