C/C++ Programmer's Guide (G06.27+, H06.08+, J06.03+)

Sharing TAL Data With TNS C Using BLOCK Declarations
As of the D20 release, TAL modules can share global data with TNS C modules by declaring each
shared variable in its own BLOCK declaration and giving both the variable and the BLOCK the
same name. The TNS C modules must also declare each shared variable; the layout of the variable
must match in both the TAL and C modules.
In this example, a TAL module declares a variable within a BLOCK declaration, and the TNS C
module declares the equivalent variable:
TAL Code C Code
NAME TAL_module;
BLOCK fred;
INT .EXT fred; int FRED; /*all uppercase*/
END BLOCK;
Because this method requires that the layout of the corresponding TAL and C declarations match,
it is recommended that you share data by using pointers where possible.
Variables and Parameters
This subsection gives guidelines for declaring compatible TAL and C variables and parameters.
These guidelines supplement those given in Sharing TAL Data With TNS C Using BLOCK
Declarations (page 109). The topics are discussed are:
• STRING and char variables
• Arrays
• Structures
• Multidimensional arrays
• Arrays of structures
• Redefinitions and unions
• Pointers
• Enumeration variables
• Bit-field manipulation
• UNSIGNED variables and packed bit fields
• TAL routines as parameters to C
• C routines as parameters to TAL
When you declare formal reference parameters, remember to use indirection:
• If the caller is a small-memory-model TNS C routine, use standard indirection (.) for the TAL
formal parameter.
• If the caller is a large-memory-model TNS C routine, use extended indirection (.EXT) for the
TAL formal parameter.
Interfacing to TAL 109