Open System Services Porting Guide (G06.29+, H06.06+, J06.03+)

not expect these opposite-environment functions to perform exactly as they would within
same-environment processes or on same-environment objects.
The syntax of the calling sequence can be different for opposite-environment functions. The semantics
is usually also different: for example, Guardian fopen() expects a Guardian filename, and OSS
fopen() expects an OSS pathname. These environment-specific functions are fopen(),
fclose(), freopen(), rename(), remove(), tmpfile(), and tmpnam(). These functions
have an explicit per-environment name: for example, fopen_oss() and fopen_guardian().
By calling the OSS variant of the function (for example, fopen_oss()) explicitly from a Guardian
program, the correct version of the function is called for the action to be taken.
You can write a module that can fit into either a Guardian or OSS program. The fread(),
fwrite(), printf(), and perror() functions will work regardless of the underlying file
environment. A stream must still be opened using the appropriate-environment version of fopen(),
however.
Although ISO/ANSI C allows the user not to use header files, any Guardian program that contains
any type of interoperable code must use the header files provided with the system to get appropriate
function prototypes and defines.
Object Type Being Manipulated
Both process and file objects exist in the Guardian and OSS environments. The functions tend to
operate on objects of their own type. All Guardian functions can manipulate Guardian objects in
a Guardian program. Some OSS functions can manipulate Guardian objects in a Guardian
program. All OSS functions that can be used in a Guardian program can manipulate OSS objects.
A general rule is that operations on an object of environment type X obey the rules of environment
X, regardless of the API in use. Thus, operations on OSS files obey POSIX.1 security rules, whether
manipulated by Guardian or OSS functions.
A Guardian process using Guardian functions can operate on Guardian objects without restriction,
but cross-object use is subject to conditions. These conditions are documented in the appropriate
reference pages. An OSS function called from a Guardian process can operate on a Guardian
object, but this use is not recommended. In such cases, the operation is governed by the restrictions
of the API (for example, can you name the given object using the expected syntax?) and by the
attributes of the Guardian process (for example, do you have enough security to do this request?).
Language or C Environment Type
The language in which the Guardian program is written and whether the program is CRE-compliant
affect what can operate or interoperate in the Guardian environment. Modules of C code can be
mixed with modules written in other languages, typically TAL. Programs with a C main() function
are CRE-compliant. Normally, the Guardian and OSS C functions exist inside programs that are
defined to be CRE-compliant. CRE provides the framework for such things as file I/O, errno, the
data heap, and so on. By default, all C programs are CRE-compliant.
All OSS functions are provided only in C language (prototype) form, and can only be called directly
from C code. However, routines in Guardian programs can be in other languages, such as TAL,
which is not always CRE-compliant. However, it is possible to call OSS functions from a Guardian
program consisting of modules written in C and in TAL. Refer to the C/C++ Programmer’s Guide
and the Open System Services Programmer’s Guide for more details on mixed-language
programming. Refer to the TAL Programmer’s Guide for details on writing CRE-compliant TAL code.
API Interoperability
API interoperability tables, listing all of the functions and macros in the Guardian C run-time library
and in the OSS C run-time library, give the programmer an overview of which functions can be
called from which module and from which process. See the Open System Services Programmer’s
Guide for complete details. See also “File Interoperability” (page 77).
148 Migrating Guardian Applications to the OSS Environment