ssize_t is from POSIX and not from the C standard

[jimsch]

The serialization code is using ssize_t rather than size_t so that it can mark errors with a negative value. The problem with this is that ssize_t is not part of standard C and therefore is not supported by all compilers.

Should we change this or should we just have non-supporting compilers re-define ssize_t appropriately?

Note that the Microsoft compiler is one of the ones which does not support this type.

[hildjj]

I would recommend defining ssize_t when needed.