Stewart wrote:
You seem to be making a distinction between the communication/transfer layer's endianness and that of the destination. That is not the distinction I make nor, I think, that Tomas is making. For me, there are two endiannesses that matter: the application's and the external, communication/transfer layer's. If the app must manipulate or inspect the data, then its endianness is, of necessity, host order. The means to transfer the data elsewhere dictates whether and to which endianness the application's order must be changed. The apps consuming that data after it leaves the first application are of no concern. (Though one might choose the external format to avoid any swapping where possible.)
Once the data reaches another application, presumably the destination in your wording, that application must deal with the communication layer's endianness and decide whether to adjust it. That swapping is wholly independent of the swapping done by the first app.
What Tomas noted is that the application's order should not change with the external endianness unless the app does nothing with the data but transfer it. In that case, the app won't use the endian library at all. OTOH, if the app does inspect of manipulate the data, then the endianness will be swapped upon importation into the app and, possibly, again on the exportation. The swapping happens at the boundaries of the application. Within the application, such data should always be in host order.
I agree with you that the over-the-wire or physical medium format is fixed and the apps must adjust. I do agree that the host must convert the data into the native format to operate on it. I do not agree that the entire message should be swapped-in-place unless performance is critical.
Your code could be as efficient as using Tomas' swap(), but not swap_in_place(), I think. Measurements are good.
Good prediction! The type-based code is more efficient than Tomas' swap() but less efficient than swap_in_place. Both approaches are equally efficient for the same-endian case. terry