System.Environment.ExpandEnvironmentVariablesCore C# (CSharp) Method

        private static string ExpandEnvironmentVariablesCore(string name)
        {
            int currentSize = 100;
            StringBuilder result = StringBuilderCache.Acquire(currentSize); // A somewhat reasonable default size

            result.Length = 0;
            int size = Interop.Kernel32.ExpandEnvironmentStringsW(name, result, currentSize);
            if (size == 0)
            {
                StringBuilderCache.Release(result);
                Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
            }

            while (size > currentSize)
            {
                currentSize = size;
                result.Capacity = currentSize;
                result.Length = 0;

                size = Interop.Kernel32.ExpandEnvironmentStringsW(name, result, currentSize);
                if (size == 0)
                {
                    StringBuilderCache.Release(result);
                    Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
                }
            }

            return StringBuilderCache.GetStringAndRelease(result);
        }