Summary
Macro
Returns return-value if NS_FAILED(nsresult) evaluates to true, and shows a warning on stderr in that case.
Syntax
NS_ENSURE_SUCCESS(nsresult, return-value);
Usage
nsresult mozMyClass::MozStringMucking()
{
  nsresult rv = NS_CStringCopy(mDestString, mSrcString);
  NS_ENSURE_SUCCESS(rv, rv);
  // this is the same as doing:
  nsresult rv = NS_CStringCopy(mDestString, mSrcString);
  if (NS_FAILED(rv))
    return rv;
  return NS_OK;
}