GAWK: Effective AWK Programming

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284 GAWK: Effective AWK ProgrammingAppendix C Implementation NotesThis appendix contains information mainly of interest to implementors and maintainers ofgawk. Everything in it applies specifically to gawk and not to other implementations.C.1 Downward Compatibility and DebuggingSee Section A.5 [Extensions in gawk Not in POSIX awk], page 260, for a summary of theGNU extensions to the awk language and program. All of these features can be turned offby invoking gawk with the ‘--traditional’ option or with the ‘--posix’ option.If gawk is compiled for debugging with ‘-DDEBUG’, then there is one more option availableon the command line:-W parsedebug--parsedebugPrints out the parse stack information as the program is being parsed.This option is intended only for serious gawk developers and not for the casual user.It probably has not even been compiled into your version of gawk, since it slows downexecution.C.2 Making Additions to gawkIf you find that you want to enhance gawk in a significant fashion, you are perfectly free todo so. That is the point of having free software; the source code is available and you arefree to change it as you want (see [GNU General Public License], page 316).This section discusses the ways you might want to change gawk as well as any considerationsyou should bear in mind.C.2.1 Adding New FeaturesYou are free to add any new features you like to gawk. However, if you want your changesto be incorporated into the gawk distribution, there are several steps that you need to takein order to make it possible for me to include your changes:1. Before building the new feature into gawk itself, consider writing it as an extensionmodule (see Section C.3 [Adding New Built-in Functions to gawk], page 287). If that’snot possible, continue with the rest of the steps in this list.2. Get the latest version. It is much easier for me to integrate changes if they are relativeto the most recent distributed version of gawk. If your version of gawk is very old, I maynot be able to integrate them at all. (See Section B.1.1 [Getting the gawk Distribution],page 265, for information on getting the latest version of gawk.)3. Follow the GNU Coding Standards. This document describes how GNU software shouldbe written. If you haven’t read it, please do so, preferably before starting to modifygawk. (The GNU Coding Standards are available from the GNU Project’s ftp site, atftp://ftp.gnu.org/gnu/GNUinfo/standards.text. An HTML version, suitable forreading with a WWW browser, is available at http://www.gnu.org/prep/standards_toc.html. Texinfo, Info, and DVI versions are also available.)
Appendix C: Implementation Notes 2854. Use the gawk coding style. The C code for gawk follows the instructions in the GNUCoding Standards, with minor exceptions. The code is formatted using the traditional“K&R” style, particularly as regards to the placement of braces and the use of TABs.In brief, the coding rules for gawk are as follows:• Use ANSI/ISO style (prototype) function headers when defining functions.• Put the name of the function at the beginning of its own line.• Put the return type of the function, even if it is int, on the line above the linewith the name and arguments of the function.• Put spaces around parentheses used in control structures (if, while, for, do,switch, and return).• Do not put spaces in front of parentheses used in function calls.• Put spaces around all C operators and after commas in function calls.• Do not use the comma operator to produce multiple side effects, except in forloop initialization and increment parts, and in macro bodies.• Use real TABs for indenting, not spaces.• Use the “K&R” brace layout style.• Use comparisons against NULL and ’\0’ in the conditions of if, while, and forstatements, as well as in the cases of switch statements, instead of just the plainpointer or character value.• Use the TRUE, FALSE and NULL symbolic constants and the character constant ’\0’where appropriate, instead of 1 and 0.• Use the ISALPHA, ISDIGIT, etc. macros, instead of the traditional lowercase versions;these macros are better behaved for non-ASCII character sets.• Provide one-line descriptive comments for each function.• Do not use ‘#elif’. Many older Unix C compilers cannot handle it.• Do not use the alloca function for allocating memory off the stack. Its use causesmore portability trouble than is worth the minor benefit of not having to free thestorage. Instead, use malloc and free.NOTE: If I have to reformat your code to follow the coding style used ingawk, I may not bother to integrate your changes at all.5. Be prepared to sign the appropriate paperwork. In order for the FSF to distributeyour changes, you must either place those changes in the public domain and submita signed statement to that effect, or assign the copyright in your changes to the FSF.Both of these actions are easy to do and many people have done so already. If youhave questions, please contact me (see Section B.5 [Reporting Problems and Bugs],page 280), or gnu@gnu.org.6. Update the documentation. Along with your new code, please supply new sectionsand/or chapters for this book. If at all possible, please use real Texinfo, instead of justsupplying unformatted ASCII text (although even that is better than no documentationat all). Conventions to be followed in GAWK: Effective AWK Programming areprovided after the ‘@bye’ at the end of the Texinfo source file. If possible, please updatethe man page as well.You will also have to sign paperwork for your documentation changes.
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