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

Memory Models
A TNS C program can use the small-memory model or the large-memory model, depending on the
amount of data storage required. The large-memory model is recommended and is the default
setting. All examples in this subsection illustrate the large-memory model unless otherwise noted.
A TAL program can use any of these memory combinations, depending on the application’s needs:
• The user data segment
• The user data segment and the automatic extended data segment
• The user data segment and one or more explicit extended data segments
• The user data segment, the automatic extended data segment, and one or more explicit
extended data segments
This table describes some aspects of memory usage by C and TAL programs. The far right column
refers to the upper 32K-word area of the user data segment.
Upper 32K-Word AreaData StorageAddressingMemory ModelLanguage
Reserved32K words16-bitSmallTNS C
Reserved127.5 MB32-bitLargeTNS C
Reserved only if you use
the CRE
64K words (without the
CRE), plus 127.5 MB in
16-bit or 32-bitN.A.TAL
each extended data
segment that is allocated
Any TAL module that uses the upper 32K-word area of the user data segment cannot run within a
TNS C object file that contains the main routine.
Data Model
The size of the C data type int is 16 bits in the 16-bit data model and 32 bits in the 32-bit data
model. (The 32-bit data model is also called the wide-data model.) If you specify the 32-bit data
model, the C data type int is 32 bits and the TAL data type INT corresponds to the C data type
short.
Any interface to a TAL routine must be specified in such a way that there is no possibility for a
data-length mismatch. Therefore, in your C program, use short for a 16-bit integer and long
for a 32-bit integer and avoid the use of int. Using short in your C program enables you to
use the same declarations regardless of the data model your program uses. The type short is
always a 16-bit integer in the C compiler.
Calling TNS C Routines From TAL Modules
A TAL module must include an EXTERNAL procedure declaration for each TNS C routine to be
called. This TAL code shows the EXTERNAL procedure declaration for C_FUNC and a routine that
calls C_FUNC. ARRAY is declared with .EXT, because C_FUNC uses the large-memory model:
TAL Code C Code
INT status := 0; short C_FUNC(char *str)
STRING .EXT array[0:4]; {
*str = 'A';
INT PROC c_func (a) str[2] = 'C';
LANGUAGE C; return 1;
STRING .EXT a; }
EXTERNAL;
PROC example MAIN;
BEGIN
Interfacing to TAL 103