Re: The joy of VAX C

Lars Poulsen <lars@beagle-ears.com> wrote:

 
 
On 26/09/2024 18:01, Lars Poulsen wrote:

On 26/09/2024 13:43, Lawrence D'Oliveiro wrote:

On Thu, 26 Sep 2024 11:49:37 +0100, Pancho wrote:
 

On 9/26/24 11:10, Lawrence D'Oliveiro wrote:

 
On Thu, 26 Sep 2024 08:42:32 +0100, Pancho wrote:
 

... a bitch to work out how to call Vax C from Vax Pascal, or vice
versa.

 
Why would it be that hard? VAX C passed everything by value, while
Pascal let you specify descriptors, references, immediate value ... all
the options.

 
There ware decisions to be made, like what order do you push variables
onto the stack, when do you push the return address, how to interpret a
Pascal String in C.

 
All these things were standardized in the VAX/VMS ABI, right from the
beginning.

 
IIRC, VAX C did not completely follow the standard calling conventions,
which created some issues in mixed-language applications.

 
In retrospect, I think the problems in mixing C with other languages
came down to this:
 
For a C routine to be callable from another language, I suspect that the
C routine would have to declare each and every argument as a descriptor
structure, the use the descriptor to find the data.
And for a C routine to call a subroutine in another language, it would
have to build a descriptor structure for that argument.
 
More trouble than anyone would want if they were used to C on any other
platform. Was that the right or the wrong choice?
An extension with a keyword like "descriptor" attached to a procedure
prototype could have made that much easier to work with!
 

IBM PL/I has that now. You can declare arguments descriptor/nodescriptor
and byaddr/byvalue.

--
Pete