System::WideString::SetLength changes theSystem::WideString::WideString’s length to newLength, truncating if necessary. 

System::WideString::SetLength reallocates the underlying array of characters that stores the value of theSystem::WideString::WideString. Existing characters in the string are preserved, but the content of newly allocated space is undefined. If there is not enough memory available to reallocate theSystem::WideString::WideString, an EOutOfMemory exception is thrown. Following a call to System::WideString::SetLength, theSystem::WideString::WideString is guaranteed to reference a unique string — that is a string with a reference count of one. 

System::WideString::Length