writing code for IPC servers

Jonathan S. Shapiro shap at eros-os.org
Thu Mar 31 22:08:49 CEST 2005

On Thu, 2005-03-31 at 10:20 +0100, Tiago Jorge wrote:
> When i come to build the stubs it with g++, it gives me error in the 
> lines that fill the exception in the call, more precisely here:
> l4_umword_t _exception = ((dice_CORBA_exception_type){ _s: { .major = 
> _dice_corba_env->major, .repos_id = _dice_corba_env->repos_id }})._raw;
> it says:
> /home/tiago/l4/pkg/ipc_example/server/src/hiworld-server.cc:17: error: parse
>    error before `.' token
> how can i adapt this line to C++ or... where is the "error".

This is a DICE bug -- or rather, an unintended C++ incompatibility.

The C99 standard introduced this syntax for "struct initialization by
name". It has not been accepted into the C++ language (yet), and I
sincerely hope that it will never be. The C99 specification of this
behavior is extremely complex and filled with ambiguity. It fails, for
example, to specify the order of initialization, and it is legal using
the by name initializers to initialize a field twice -- once in the old
style and a second time using the new syntax. The results are both
unchecked and unspecified.

Because this area of the C99 standard is exceedingly complicated, I
would strongly urge the DICE team to avoid use of this feature. There is
nothing conceptually wrong with it, but current compilers cannot be
relied on to implement this feature correctly in complex cases. Using
this feature is therefore inadvisable *even* if C is the only intended
target langauge.

Avoiding it would incidentally avoid a gratuitous C++ incompatibility,
and would help ensure that all initializers are completely specified by
making it impossible to omit fields accidentally from the initialization

Jonathan Shapiro

More information about the l4-hackers mailing list