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Q46773: Using C Run-Time Library Functions in .DLLs

Article: Q46773
Product(s): See article
Version(s): 5.10
Operating System(s): OS/2
Keyword(s): ENDUSER | SR# G890705-21975 | mspl13_c
Last Modified: 25-JUL-1989

Question:

In a .DLL, what C standard library functions are usable?

Also, one reference mentions special re-entrant libraries for use in
.DLLs. Is that correct, and if so, how do you get at them? Is there
some place where this information is documented?

Response:

There's been a lot of confusion about the proper way to write .DLLs
because what was legal and what's not legal has changed at least once
during the lifetime of the OS/2 SDK.

In the past, there were restrictions on which library functions you
could use and how you could use them. These restrictions have been
removed because we've created several specially-modified libraries
that can be used freely in .DLLs. All library functions can be called.
Any serialization needed is handled by the library.

The proper way to create .DLLs is outlined in the file MTDYNA.DOC,
which is included with the C 5.10 compiler. There are also examples
included with the compiler that you can compile and modify. If you are
developing for OS/2 1.10, instead of OS/2 1.00, with the OS/2 1.10
Software Development Kit or Tool Kit, use the OS/2 1.10 library
OS2.LIB in place of the OS/2 1.00 library DOSCALLS.LIB. Also make sure
to include the OS/2 1.10 include files before, or instead of, the C
5.10 regular and multi-thread include files with the same names, such
as OS2.H and BSE.H. These C 5.10 OS/2 API-related include files are
for OS/2 1.00.

Note: There are two very important details about writing your .DEF
file that MTDYNA.DOC doesn't mention:

1. You MUST use a DATA MULTIPLE NONSHARED statement for any .DLL that
   uses the C run-time library because each process that uses the .DLL
   needs its .DLL to have a separate data area. Otherwise, multiple
   instances of the .DLL will corrupt each other's C run-time library
   static data.

2. You also MUST use LIBRARY INITINSTANCE in any .DLL that calls the
   C run-time library because each instance of the .DLL must have its
   run-time library data area initialized separately.

Aside from these two details and the new OS/2 1.10 library and header
files, MTDYNA.DOC is an excellent guide for writing .DLLs.

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