What does Array.Clear actually do under the covers?

Question

I'm looking for a answer to what the Array.Clear(...) method does under the covers in C#.

I've looked at the IL, but that isn't really yielding any clues, since it simply calls the System.Array::Clear(...) method in mscorlib, which then calls an unmanaged portion of the CLR that I can't observe.

The reason why I am asking this, is that I am occasionally getting an SEHException thrown by my call to Array.Clear, and I can't seem to figure out why it is happening.

Unfortunately, Microsoft seems to be a little tight-lipped about what it might mean when the exception is thrown...

From: http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.sehexception(v=VS.100).aspx

Any SEH exception that is not automatically mapped to a specific exception is mapped to the SEHException class by default. For more information, search on "unmanaged exceptions" and "Structured Exception Handling" in the MSDN Library.

Answer 1

You can see that kind of code in the SSCLI20 source code. Which looks like this with all the noise removed:

FCIMPL3(void, SystemNative::ArrayClear, ArrayBase* pArrayUNSAFE, INT32 iIndex, INT32 iLength)
{
    BASEARRAYREF pArray = (BASEARRAYREF)pArrayUNSAFE;
    // error checks
    //.. 
    char* array = (char*)pArray->GetDataPtr();
    int size = pArray->GetMethodTable()->GetComponentSize();
    ZeroMemory(array + (iIndex - lb) * size, iLength * size);
}

In other words, it simply blasts 0 bytes into the elements. The only way to get an SEHException is through a processor fault. GC heap corruption. Review any pinvoke or COM interop code.