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Chapter 16: Software Development
This is a short overview of some common programming languages. Our aim here is to give you a general idea of what tools are available, and how they can be used. The list is ordered from low to high level, and indicates common uses:
not used at Fermilab
system services, user interface, general utilities
FORmula TRANslation (physics calculations)
object oriented general programming
interpreter, general purpose
object-oriented and/or general purpose interpreted scripting language
interpreter, GUI interfaces
Traditionally, assembler has been needed for a couple of reasons:
Assembler programming is not generally necessary or desirable on the RISC based UNIX systems presently in use. RISC system performance is so heavily dependent on pipelining and various caches that it is extremely difficult, if not impossible, for an individual to write more efficient assembler code than is generated by the higher level language compilers. The C language provides all the hardware access and system service capabilities traditionally provided by Assembler.
As noted above, C has filled the programming niche traditionally occupied by Assembly language. In addition to its normal use as a high-level programming language, C can act as a universally portable Assembler.
Because the C language was created, has evolved, and has become standardized hand-in-hand with the UNIX operating system, it is the language of choice for applications involving system services and user interfaces. Using C is discussed in several of the following sections.
Now that an ANSI C standard exists and is widely implemented, portability of C code is much improved. ANSI C compilers are the default on most Fermilab systems. Likewise, adoption and availability of POSIX standards for operating system services has greatly improved program portability.
An excellent reference book for C programming is The C Programming Language by Kernighan and Ritchie published by Prentice-Hall.
FORTRAN remains the most effective language for mathematical calculations. This is due partly to decades of research which has produced highly efficient optimizing compilers, and partly to the millions of lines of tested, portable code already in use.
C++ adds object oriented programming constructs to the C language. At the risk of oversimplifying, it seems that C++ is substantially harder to learn and to use for writing new programs, but the resulting programs are much better structured, more maintainable, and more shareable than traditional C or FORTRAN programs.
An additional advantage of C++ is the availability of class[75] libraries. A Standard Template Library will come with most compilers soon. This library will contain many useful low level classes for such things as strings and streams I/O. Also, some vendors include other commercial class libraries as added value to their compilers. In addition to the vendor-supplied versions, C++ is available as a part of Gnu C. This has increased its popularity.
The C++ language standard is (still!) in the process of adoption by the ANSI and ISO standards committees. Since the C++ standard has not been finalized (although it changed significantly in December 1996), there are at this time (November 1997) cross-platform porting issues. None of our major vendors (SGI, IBM, GNU) are yet providing a draft-standard-compliant compiling and runtime toolkit. The safest bet for generating portable C++ code is to avoid using newer features such as exceptions and templates, which may be implemented differently (or not at all) by the various C++ compiler vendors, at least until the vendors catch up with the standard. As an alternative, use the g++ command to run the Gnu integrated C/C++ compiler on all platforms. Using the g++ command instead of gcc gives you appropriate C++ linking.
For documentation, you may refer to:
CC (upper case), gcc and g++ command man pages
perl is installed at Fermilab as part of the shells product. The man page for perl gives a good brief description:
There is an excellent text published by O'Reilly & Associates, Inc. on perl.
Python is an interpreted, interactive, object-oriented programming language often compared to Tcl, Perl, Scheme and Java. Python combines remarkable power with very clear syntax. It has modules, classes, exceptions, very high level dynamic data types, and dynamic typing. There are interfaces to many system calls and libraries, as well as to various windowing systems (e.g., X11, Motif, Tk, Mac, MFC, STDWIN). New built-in modules are easily written in C or C++. Python is also usable as an extension language for applications that require a programmable interface.
An on-line document for Python is available in the CD documentation database.
Tk is an X11 toolkit that provides the Motif look and feel, and is easy to use for building graphical interfaces largely because it is built on an interpreted language. It can be used with a variety of languages including Tcl (Tk used to be solely implemented using Tcl), Perl, and Python.
The best reference for Tk is the book Tcl and the Tk Toolkit[76], by John K. Ousterhout, published by Addison-Wesley. The README file under the tk directory in $TK_DIR (created during setup) points to a draft of this book. Also see the man pages for information on these languages.
Other tools exist that are commonly used as languages in the appropriate context. These include, for example, the various UNIX shells (as discussed in section 4.4), and awk, sed, yacc, and lex, for which O'Reilly & Associates, Inc. provides excellent texts.
There are many other languages which are not widely supported or are not in general use at Fermilab. These include Pascal, Modula-2, Lisp, Forth, Bliss, and others. We do not discuss them in this document.