Q44477: Use /ND Instead of #pragma data_seg

Article: Q44477
Product(s): See article
Version(s): 5.10   | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 26-MAY-1989

Support for the data_seg pragma may be eliminated from future versions
of the Microsoft C Optimizing Compiler. Microsoft strongly recommends
that you use the /ND option at compile time instead of embedding the
data_seg pragma in your source code.

When you use /ND to change the name of the default data segment for a
given module, your program can no longer assume that the address
contained in the stack segment register (SS) is the same as the
address in the data segment (DS). You must also compile with /Au or
use the _loadds keyword. A _loadds function loads its own data segment
upon entry.

All modules whose data segments have the same name have these segments
combined into a single segment at link time, including all data that
would otherwise be allocated in the _DATA segment, i.e., all
subsequent initialized static and global data.

See the "Microsoft C 5.1 Optimizing Compiler User's Guide," Section
6.7, "Naming Modules and Segments," Pages 157-159, for more detail.

The data_seg pragma specifies the name of the data segment that
subsequent _loadds functions should use and also causes the named
segment to contain all data that would otherwise be allocated in the
_DATA segment.

Note that the use of pragma data_seg by itself does not cause
subsequent functions to load DS. You must also compile with /Au or use
the _loadds keyword.

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