z/OS XL C/C++

With the XL C/C++ compiler feature of z/OS, you can produce high-performing z/OS-based XL C/C++ programs to provide optimized business software solutions. The z/OS XL C/C++ compiler is part of the family of IBM XL C/C++ compilers that adhere to international standards to allow for easier portability of applications to z/OS from both IBM and non-IBM platforms.

IBM z/OS XL C/C++ provides the following features, common to both XL C and XL C/C++ compilers:

- z/OS UNIX System Services (z/OS UNIX) support, including the use of the z/OS UNIX Hierarchical File System (HFS) and/or the z/OS Distributed File Service zSeries File System (zFS) for storage of compiler source and output. The z/OS UNIX Shell and Utilities feature provides the c89, c99, and cxx commands for invoking the z/OS XL C/C++ compilers, the Language Environment Prelinker, and the system binder.

- Coded character set (code page) support, the compiler can process C and C++ syntax characters (such as square brackets) regardless of which Latin-1 EBCDIC coded character set is used to create the source file.

- DSECT Conversion Utility for converting descriptive data produced by the High Level Assembler licensed program into C/C++ data structures, for XL C/C++ programs that interface with assembler programs.

- DLL support for generating Dynamic Link Libraries (DLLs) similar to the way Windows® DLLs are generated. DLLs allow a function call or a variable reference in one load module to use a definition located in another load module at run time. DLL support is also available in the z/OS UNIX environment.

- Full program reentrancy for C/C++ programs.

- Interlanguage calls between C and C++ programs, and between C or C++ programs and assembler, COBOL, PL/I or Fortran programs.

- Language Environment preinitialized interface support for greater efficiencies when invoking a C or C++ program repeatedly from a PL/I or assembler program.

- Longname support so external names can be mixed case and up to 1024 characters long.

- Optimization of C and C++ code, using the OPT compiler option, in which the compiler changes unoptimized or inefficient code sequences. This includes such things as:

• Inlining, or replacing of certain function calls with the actual code of the function being performed

• Value numbering, which involves local constant propagation, local expression elimination, and folding several instructions into a single instruction

• Straightening, which rearranges program code to minimize branch logic, and combines physically separate blocks of code

• Common (or duplicate) expression elimination

• Code motion, or performing calculations outside a loop (if the variables in a loop are not altered within that loop) and using the results within that loop

• Strength reduction, in which less efficient instructions are replaced with more efficient ones

• Constant propagation, where the compiler combines constants used in an expression and generates new ones

• Instruction scheduling, where the compiler reorders instructions to minimize program execution time

• Dead store elimination, where the compiler eliminates stores when the value stored is never referred to again

• Dead code elimination, where the compiler eliminates code for calculations that is not required

- The compiler also performs both intraprocedural and interprocedural analysis. Intraprocedural analysis is a mechanism for performing optimization on each function in a compile unit, using only the information available for that function and compilation unit. Interprocedural analysis is a mechanism for performing optimization across source file boundaries. You can invoke interprocedural analysis by using a compiler option. It performs optimizations that are not otherwise available with the XL C/C++ compiler.

- C/C++ support for the z/OS UNIX environment, allowing application developers to use C or C++ to build z/OS UNIX applications.

- National Language Support to allow dynamic switching between English and Japanese messages.

In addition to the features common to z/OS XL C and XL C++, the z/OS XL C compiler provides you with the following capabilities:

- The ability to write portable code that supports the following standards:

• ISO/IEC 9899:1999

• ANSI/ISO 9899:1990[1992] (formerly ANSI X3.159-1989 C)

• X/Open Specification Programming Language Issue 3, Common Usage C FIPS-160

• FIPS-160

- System programming capabilities, which allow you to use z/OS XL C in place of assembler

• the __asm keyword allows the programmer to specify assembly instructions in C code

• the METAL compiler option allows the developer to use the MVS(TM) system linkage conventions

• the PROLOG and EPILOG compiler options and the #pragma prolog() and #pragma epilog() preprocessor directives allow the programmer to specify custom HLASM prolog and epilog code, to implement custom function linkage conventions if required

- Additional optimization capabilities through the INLINE compile-time option

- Extensions of the standard definitions of the C language to provide programmers with support for the z/OS environment, such as fixed-point (packed) decimal data support

In addition to the features common to z/OS XL C and XL C++, the z/OS XL C++ compiler supports the International Standard for the C++ Programming Language (ISO/IEC 14882:1998) specification. Also, it further conforms to the Programming languages - C++ (ISO/IEC 14882:2003(E)) standard, which incorporates the latest Technical Corrigendum 1.

When used with z/OS UNIX System Services and z/OS Language Environment, the z/OS XL C/C++ compilers provide support for the following standards at the system level:

• A subset of ISO/IEC 9899:1999

• ISO/IEC 9945-1:1990 (POSIX-1)/IEEE POSIX 1003.1-1990

• A subset of IEEE POSIX 1003.1a, Draft 6, July 1991

• IEEE Portable Operating System Interface (POSIX) Part 2, P1003.2

• A subset of IEEE POSIX 1003.4a, Draft 6, February 1992 (the IEEE POSIX committee has renumbered POSIX.4a to POSIX.1c)

• X/Open CAE Specification, System Interfaces and Headers, Issue 4 Version 2

• A subset of IEEE 754-1985 (R1990) IEEE Standard for Binary Floating-Point Arithmetic (ANSI), as applicable to the S/390® environment.

• X/Open CAE Specification, Network Services, Issue 4

Displayable BookManager and PDF (softcopy) versions of most publications are available on CD with the z/OS Software Products Collection (SK3T-4270).

For a fee, you can order additional copies of the softcopy collection from the IBM Publications Center at:
http://www.ibm.com/shop/publications/order

For other publication ordering options, see:
http://www.ibm.com/servers/eserver/zseries/zos/bkserv/order_books.html