hi here's the monthly :-) revised faq
Russ russwhit@mind.net ++++++++++++++++++++++++++++++++++++++++++++++++
GNU Pascal Frequently-Asked Questions List, Edition 0.7, May 2000 by Russ Whitaker russwhit@mind.net
based on GNU Pascal Frequently-Asked Questions List, Edition 0.4, for GPC version 2.0, November 1996 by J.J. van der Heijden j.j.vanderheijden@student.utwente.nl
For up-to-date information, ask the GPC mailing list (see below).
Index ***** 1.0 GNU Pascal - what, where and why 2.0 Installation 3.0 After the installation 4.0 Pascal on the DJGPP platform 5.0 (reserved) 6.0 Getting Help 7.0 Miscellaneous
1.0 GNU Pascal ***************
1.1 What and why? =================
The purpose of the GNU Pascal project is to produce a Pascal compiler (called GNU Pascal or GPC) which
* combines the clarity of Pascal with powerful tools suitable for real-life programming,
* supports both the Pascal standard and the Extended Pascal standard as defined by ISO, ANSI and IEEE (ISO 7185:1990, ISO/IEC 10206:1991, ANSI/IEEE 770X3.160-1989),
* supports other Pascal standards (UCSD Pascal, Borland Pascal, Pascal-SC) in so far as this serves the goal of clarity and usability,
* may be distributed under GNU license conditions,
* can generate code and run on any computer for which the GNU C compiler can generate code and run on.
Pascal was originally designed for teaching. GNU Pascal provides a smooth way to proceed to challenging programming tasks without learning a completely different language.
1.2 What is the current version? ================================
The latest release as of this writing is GPC-19991030. GPC requires GCC as a back-end. Patches for GCC 2.8.1 thru GCC 2.95.2 are provided but it is recommended that you use at least GCC 2.95.
1.3 Is it compatible with Turbo Pascal (R) ? ============================================
GPC is *not* a drop-in replacement for Borland's Turbo Pascal (R). Almost all BP language features are supported. Notable exceptions are the string format (as discussed below), or the 'Mem' and 'Port' pseudo arrays, though replacement functions for the latter on x86 platforms exist in the 'Ports' unit.
Also, almost all of BP's run time library is supported in GPC (built-in or in units with the same names as their BP counterparts).
Some notes:
- A BP compatible Graph unit exists but is distributed separately due to its license.
- The OOP stuff (Turbo Vision etc.) is not yet completed, but work on several projects is underway.
- Some exotic routines need an explicit `uses System' statement, or equivalently a `--uses=system' command line option. See the System unit for details.
- A few unportable routines in the Dos unit are only supported under DJGPP if `__BP_UNPORTABLE_ROUTINES__' is defined (i.e., when com- piling with `-D__BP_UNPORTABLE_ROUTINES__').
---Frank
1.4 Which platforms are supported by GNU Pascal? ================================================
GPC uses the GCC backend, so it should run on any system that is supported by GNU CC. This includes a large variety of Unix systems, MS-DOS, OS/2 and Win32. A full list of platforms supported by GCC can be found in the file `INSTALL' of the GCC distribution. Not all of these have actually been tested, but it is known to run on these platforms:
ix86-linux (Linux 2.x, ELF) i486-linuxaout i486-linuxoldld i386-freebsd1.2.0 AIX 4.2.1 AIX 4.3 DJGPP V2 (msdos) EMX 0.9B (OS/2, msdos) cygwin32 beta20 and higher (Windows95, Windows NT) Mingw32 (Windows95/98, Windows NT) mips-sgi-irix5.3 sun-sparc-sunos4.1.4 sparc-sun-solaris2.x sun-sparc-solaris 2.5.1 sun-sparc-solaris 2.6 sun-sparc-solaris 7 alpha-unknown-linux alphaev56-dec-osf4.0d
Ok people - send us your success stories, with canonical machine
name! <<<
2.0 Installation *****************
2.1 Why shouldn't I just grab and install a binary? ===================================================
On many platforms a binary is a quick and easy way to go. With Linux, however, you may have a problem. Many of the installation details are left up to the implementor and if that isn't enough updating a seemingly unrelated piece of software can cause compatibility problems. Witness this exchange from the mailing list:
>>I'm not an expert on this, but I remember that I installed on my Linux >>(RedHat 6.1) two RPM packages: >> >> gpc-19990118-1.i386.rpm >> gpc-extras-19990118-1.i386.rpm > I have install all but it doesn't run anyway! > My Linux is mandrake 7.0, it is maybe the problem?...
Mandrake is NOT compatible with RedHat despite claims - you need less manual tweaks then in case with SuSE or Debian but ONLY RedHat is compatible with RedHat (even in this case only if you are lucky enough - see below). ESPECIALLY for GPC: Mandrake traditionally using very "advanced" (read: barely working) versions of gcc and gpc relies HEAVILY on gcc.
If you DO NOT have RPM for EXACTLY your distribution then better (=easier) to recompile GPC from sources. And when I'm saying EXACTLY I mean exactly: RPM for RedHat 5.0 WILL NOT work in RedHat 5.2, RPM for RedHat 6.0 WILL NOT work in RedHat 6.2, etc. In some cases even "RedHat x.y" can be incompatible with "RedHat x.y with updates" :-(( Usually it can be easily tracked down and fixed by knowledgeable person (almost any package for any distribution can be forced to work in almost any other distribution) but just "rpm -Uvh" quite often will not work. When you are compiling program from sources autoconf usually can find and compensate most differences automagically but rpm/dpkg/apt is NOT sophisticated enough. That's why we recommend to start from sources when binaries do not work for you.
2.2 How do I get and install GPC on my computer? ================================================
1. The easiest way is is from a distribution - if you can find it. All the dependency files should be there, also. The downside is if the GPC release date is prior to Oct. 1999 you should plan on doing an update.
2. The recommended way is to build it yourself from the source listings. If you have everything you need to compile a kernel except the kernel source then all you need is the GPC source and a GCC source. The down- side is if you have a slow computer the build could take several hours.
You can get the GPC source from
ftp://agnes.dida.physik.uni-essen.de/
You can get the GCC source from
3. You may not want to install a new distribution just to get GPC and the build project on a 386 can take several hours as well as some 50M of hard drive space. Then try one of the several pre-compiled binaries available. The downside is you need one that is compatible with your computer and C library.
GNU Pascal Compiler binaries for Sun Solaris 7 (Sparc/x86) operating environment in native Solaris packages form are available at:
Sparc: ftp://mizar.uwb.edu.pl/pub/misc/solaris7/sparc http://math.uwb.edu.pl/download/solaris7/sparc
x86: ftp://mizar.uwb.edu.pl/pub/misc/solaris7/x86 http://math.uwb.edu.pl/download/solaris7/x86
For installation instructions read Readme.txt file on that site.
GPC 19991030 was compiled based on GCC 2.95.
Binaries for Solaris 8 (Sparc and Intel) are now available on: http://math.uwb.edu.pl/download/solaris8/ ftp://mizar.uwb.edu.pl/pub/misc/solaris8/
-- Mariusz Zynel
Also, on Feb 9th, 2000 the following binaries were found in a FTP directory at agnes.dida.physik.uni-essen.de:
Directory: /gnu-pascal/alpha/binary/
gpc-19990607-djgpp.zip
Directory: /gnu-pascal/beta/binary/
gpc-19990118-1.i386-pc-linux-gnu.rpm gpc-19990118-egcs-1.1.1.i386-linux-glibc2.tar.gz gpc-19990118-egcs-1.1.1.i386-pc-mingw32.zip gpc-19990118-egcs-1.1.1.i586-pc-linux-gnulibc1.tar.gz gpc-19990118.alpha-unknown-linux-gnu.tar.gz gpc-19990118.alphaev56-dec-osf4.0d.tar.gz gpc-19990118.i386-pc-djgppv201.zip gpc-19990118.i386-pc-emx0.9d.zip gpc-19990118.i386-pc-mingw32.zip gpc-19990118.i586-pc-linux-gnulibc1.tar.gz gpc-19990118.mips-sgi-irix6.2.tar.gz gpc-19990118.sparc-sun-solaris2.6.tar.gz gpc-19990430-i386-pc-djgppv202.zip gpc-extras-19990118-1.i386-pc-linux-gnu.rpm
2.3 How do I build a GPC compiler? ==================================
CAUTION: There have been extensive changes in GCC from 2.8 to 2.95. The old GPC build instructions, for GCC-2.8 and earlier, will not work on GCC-2.95 and up.
If you have a typical ix86 box the routine is fairly simple. Any other computer you should carefully read the documentation in gcc*/install.
Assuming you have:
1. A working C compiler. 2. The usual tools: ar, awk, bash, bison, ld, make, patch, sed 3. The GPC and GCC tar.gz source in directory /usr/local/src
Then here's a cookbook recipe:
1. Unpack the two sources: tar -xvzf gcc-2.95.2.tar.gz tar -xvzf gpc-19991030.tar.gz
2. Since GCC recommends building gcc in a separate directory, lets make one: we'll call it gcc-build. mkdir gcc-build
3. Now we need to move GPC into GCC: mv gpc/p gcc-2.95.2/gcc
NOTE: Don't try using a symlink instead. This is known not to work. You have to actually move the directory.
4. Next is a patch to GCC: cd gcc-2.95.2/gcc patch -s -p1 < p/diffs/gcc-2.95.2.diff
However, since the configure script will apply the patch automatically when necessary, you can usually skip this step.
5. Now GCC is ready to build several languages, including Pascal. If you want to know what languages (besides C), grep language= */config-lang.in will give you a list.
6. Next step is to do a configure: cd ../../gcc-build ../gcc-2.95.2/configure --enable-languages=pascal
This will configure the compiler for installation under /usr/local. If you want to install it in another place, e.g. /usr or in your home directory, you can specify this with the '--prefix' option: ../gcc-2.85.2/configure --enable-languages=pascal --prefix=/home/me/usr (note: one line - it's two here because of length)
If configure complains that it couldn't figure out what your computer is, for a Linux system and a pentium or pentium II you should add --host=i586-linux-gnu to the configure line. You can find values for other hosts in either the GCC documentation or chapter 3 of Richard Stallman's book, "Using and Porting GNU CC".
The following text assumes default configuration: under /usr/local.
With --enable-languages=pascal you get both GCC and GPC. The GCC won't interfere with your default compiler because it is installed in a different place. Without the --enable-languages option you get ALL the languages GCC can build.
7. Now let's build it: make bootstrap-lean
Bootstrap-lean is recommended instead of bootstrap because it removes files that are no longer needed. That "make bootstrap-lean" will take some time. If you want to know how much, you could date > /time1 ; make bootstrap-lean ; date > /time2
On my 400mhz i586 with 128m ram, no swap, it took 24 min 34 sec.
8. If all went well you can now install it: make install
You have to do this last step as root (Unless configured for installation in your home directory), while the other steps can be done under a normal user ID.
That's it. Here's where various parts of GPC are installed:
/usr/local/bin/gpc The GPC executable /usr/local/info/gpc.info* Info documentation /usr/local/man/man1/gpc.1 Man page (contains only an extract from the Info documentation) /usr/local/doc/gpc/* Some texts about GPC, including this FAQ /usr/local/doc/gpc/demos/* Some interesting demos
GPC's units are installed in a directory whose name you can find with gpc --print-file-name=units after installation. If this doesn't give the correct directory (or
just says 'units'), your installation is not quite right yet.
If you run into installation problems the following might help: gpc --print-search-dirs
3.0 After the Installation **************************
3.1 What to do first? =====================
Stop right now and go read the file BUGS in directory
/usr/local/doc/gpc
While you're at it, you should take a look at the other files in that directory:
README General Information about GPC AUTHORS List of GPC authors NEWS Changes since the last beta version COPYING GNU General Public License COPYING.LIB GNU Library Public License
Another good article on submitting bug reports can be found at
either: http://www.chiark.greenend.org.uk/~sgtatham/bugs.html or: http://freshmeat.net/news/2000/02/26/951627540.html
3.2 What additional libraries should I have? ============================================
You will need certain additional libraries when you compile some of the units. These can be found in the directory
ftp://agnes.dida.physik.uni-essen.de/gnu-pascal/libs
What follows is the contents of the README file found there:
In this directory, you can find the libraries used by some of GPC's units. Currently, there are the following libraries:
- gmp:
Arithmetic for integers, rationals and real numbers with arbitrary size and precision. Used by the GMP unit.
- rx:
Regular expression matching and substitution. Used by the RegEx unit.
- ncurses, PDCurses:
Screen handling. Used by the CRT unit. Depending on your system, you have the following choices:
Unix: You can compile terminal applications with ncurses and applications that run in an X11 window with PDCurses (though terminal applications can, of course, also run in an xterm under X11). ncurses is used by default. If you want to use PDCurses (a.k.a. XCurses), give the option `-DX11' when compiling CRT.
Dos with DJGPP and MS-Windows with mingw: Only PDCurses is available and will be used by default.
MS-Windows with Cygwin: PDCurses and ncurses are available. PDCurses is used by default. If you want to use ncurses, give the option `-DUSE_NCURSES' when compiling CRT.
Other systems: Please see the `README's and installation instructions of PDCurses and ncurses to find out which one(s) can be built on your system. See the conditionals at the end of crt.inc and crtc.h (and change them if necessary) on which library is used by default.
The source code of the libraries is available in this directory. Most libraries come with one or several patches which should be applied before compiling them.
Binaries for some platforms are available in the `binary/<platform>' subdirectories. If you compile the libraries for other platforms, be invited to make the binaries available to us for distribution on this FTP site.
There are also the following files:
- terminfo-linux.tar.gz This is a patch to enable ncurses programs to make use of the ability of Linux 2.2 and newer kernels to produce a block cursor when needed. The present patch can be installed without recompiling anything, just by copying some files into place. More details can be found in the `README' file included in this archive. The patch will not do any harm on older kernels. Please note that *not* only on Linux machines it is useful to install the patch. Installing them on any other machine will allow users who telnet in from a Linux console to profit from the block cursor capability. Besides, some Unix systems have installed older Linux terminfo entries or none at all, so it's a good thing, anyway, to give them a current version. The patch is included in the terminfo database of ncurses 5.0, so if you install ncurses 5.0 (source or binary), you don't need to get the patch separately. But you can install it on a system with an older ncurses version if you don't feel like upgrading ncurses altogether.
- tsort-2.9i.zip A little utility (extracted from util-linux-2.9i, but not Linux specific), needed for the configuration of the rx library. You need it only if you compile rx yourself (and if it's not already present on your system), not when using a rx binary.
In addition to the above libraries there is a unit which you can use to interface Svgalib. You can read a mini-FAQ about it at
http://ages.dida.physik.uni-essen.de/~nicola
complete with links to download the unit via http or ftp. If you want to download the unit directly, get svgalib-gpc-20000216.tar.gz from
ftp://agnes.dida.physik.uni-essen.de/home/nicola
3.3 Which components do I need to compile Pascal source code? ==============================================================
A complete Pascal compiler system should at least have:
1. The actual compiler, GPC. While there are some binaries available you can build GPC yourself. You need a working C compiler, some tools: bash, ar, patch, make, the GCC source, and the GPC source.
2. An editor, assembler, linker, librarian and friends.
3. A C library. If you have a working C compiler you already have this.
4. A debugger, if you want to debug your programs.
For most people, the GNU binutils and GNU debugger (gdb) are a good choice, although some may prefer to use vendor specific tools.
3.4 How do I debug my Pascal programs? =======================================
To debug your programs, (a) GNU Pascal must be able to generate executables with debug info for your platform, and (b) you must have a debugger which understands this.
* If `gpc -g -o hello hello.p' says: `gpc: -g not supported for this platform', then GPC is unable to generate debug info. Usually, installing GAS instead of your system's assembler can overcome this. When you configure the GCC used for GPC, specify `-with-gnu-as', and possibly `-with-gnu-ld' and/or `-with-stabs'. More information can be found in `INSTALL' file in the GNU CC source directory.
* Your system's debugger may not understand the debug info generated by GNU tools. In this case, installing GDB may help.
The bottom line: if you can debug GCC compiled programs, you should be able to do this with GPC too.
The GNU debugger (GDB) currently does not have a "Pascal" mode, so it is unable to display certain Pascal structures etc. When debugging, please note that the Initial Letter In Each Identifier Is In Upper Case And The Rest Are In Lower Case. If you want to display variable `foo' in the debugger, type `show Foo' or `display Foo' instead.
3.5 Can you recommend an IDE? ==============================
Users of Borland Pascal may wonder if there's a replacement for the IDE (Integrated Development Environment). Here's a few suggestions:
* (X)Emacs. Some people think it's the answer to the question of Life, the Universe and Everything, others decide it's uGNUsable. Available from your friendly GNU mirror and most distributions.
* XWPE is an imitation of the Borland IDE, so users of Borland Pascal may find it a good alternative.
* RHIDE. DJGPP users should definitely try RHIDE. The latest (beta) release is compatible with GNU Pascal and allows stepping, tracing and watching like Borland's IDE. It can be downloaded from:
http://www.tu-chemnitz.de/~sho/rho/rhide/rhide.html
* PENG. It's not free software, but it was written with GPC. It's very similar to Borland's IDE, but with many extensions:
3.6 Debugger? ==============
Although GDB is an excellent debugger, it's user interface is not very attractive. Refer to the comp.windows.x FAQ: "Where can I get an X-based debugger?" at:
http://www.cis.ohio-state.edu/hypertext/faq/usenet/x-faq/part6/faq-doc-2.htm l
Some useful frontends include: XXGDB, tGDB and XWPE. see:
http://www.ee.ryerson.ca:8080/~elf/xapps/Q-IV.html
Very nice, but resource consuming is the Motif based DDD:
http://sol.ibr.cs.tu-bs.de/softech/ddd/
4.0 GNU Pascal on the DJGPP (MS-DOS) platform *********************************************
This chapter discusses some potential problems with GNU Pascal on MS-DOS, using DJGPP.
What is DJGPP? ==============
The following paragraph is from the site www.delorie.com/djgpp:
DJGPP is a complete 32-bit C/C++ development system for Intel 80386 (and higher) PCs running DOS. It includes ports of many GNU development utilities. The development tools require a 80386 or newer computer to run, as do the programs they produce. In most cases, the programs it produces can be sold commercially without license or royalties.
If you need more information ============================
GPC/DJGPP is a DJGPP V2 application, and most of the DJGPP documentation applies for GPC too. A great source of information is the DJGPP FAQ:
http://www.delorie.com/djgpp/v2faq/230b.zip
Another place to look for DJGPP documentation is the DJGPP Knowledge Base, at this URL:
http://www.delorie.com/djgpp/doc/kb/
What do I download? ===================
As discussed in section 2.2, other than GPC itself, you need an assembler, linker and friends, a C library and possibly a debugger. The site www.delorie.com/djgpp recommended the following files and they will help you find a mirror:
v2/djdev203.zip (C library) v2gnu/bnu2951b.zip (assembler, ....) v2gnu/gcc2952b.zip (gcc) v2gnu/gdb418b.zip (debugger) v2gnu/mak379b.zip (make) v2gnu/txi40b.zip (texi)
This list is 10,553,416 bytes not counting GPC. You can use a binary version of GPC from agnes.
How do I install the compiler? ==============================
If you don't have djgpp installed on your harddisk, create a directory for GNU pascal (`c:\gpc'), and unzip the archives. Make sure you preserve the directory structure (use `pkunzip -d'). Now, add the directory where `gpc.exe' lives (`c:\gpc\bin') to your path and set the DJGPP environment variable to point to your `djgpp.env' file:
set DJGPP=c:\gpc\djgpp.env
Then, add this to your `djgpp.env' file:
--------------------------------------------------------- [gpcpp] C_INCLUDE_PATH=%/>;C_INCLUDE_PATH%%DJDIR%/lang/pascal; %DJDIR%/include;%DJDIR%/contrib/grx20/include ( note: one line; but split here to fit page )
[gpc] COMPILER_PATH=%/>;COMPILER_PATH%%DJDIR%/bin LIBRARY_PATH=%/>;LIBRARY_PATH%%DJDIR%/lib;%DJDIR%/contrib/grx20/lib ---------------------------------------------------------
The binary distribution should come with a `djgpp.env' which is already modified, so you may not have to do this.
The GPC online documentation is in GNU info format; you need the Info reader (`txi390b.zip') to read it, or use the built-in Info reader of the RHIDE or PENG IDE. To add the GPC documentation to the info directory file, edit the `c:\gpc\info\dir' file, and locate this section:
--------------------------------------------------------- * GCC: (gcc.inf). The GNU C, C++, and Objective-C Compiler
* GDB: (gdb.inf). The GNU Debugger (gdb and gdb-dpmi).
---------------------------------------------------------
To add GPC, change it to look like this:
--------------------------------------------------------- * GCC: (gcc.inf). The GNU C, C++, and Objective-C Compiler
* GPC: (gpc.inf). The GNU Pascal Compiler
* GDB: (gdb.inf). The GNU Debugger (gdb and gdb-dpmi).
---------------------------------------------------------
Specific information for low-memory conditions and more can be found in the DJGPP FAQ and documentation.
I cannot read the Info documentation! =====================================
To read the Info documentation, you need the `info' program from `txi390b.zip' or an IDE like RHIDE or PENG.
GPC says: no DPMI =================
You don't have a DPMI server installed, and DJGPP v2 requires it to run. You can either use one of the commercial DPMI servers (e.g., run `gpc' in a DOS box under Windows) or download and install CWSDPMI (`csdpmi3b.zip') which is a free DPMI server written for DJGPP.
I have troubles with assembly code ==================================
The GNU Assembler (`as.exe'), or `gas', called by GCC accepts "AT&T" syntax which is different from "Intel" syntax. Differences are discussed in section 17.1 of the DJGPP FAQ.
A guide is available which was written by Brennan Mr. Wacko Underwood brennan@mack.rt66.com and describes how to use inline assembly programming with DJGPP, at this URL:
http://www.rt66.com/~brennan/djgpp/djgpp_asm.html
There's also a GPC assembler tutorial at
ftp://agnes.dida.physik.uni-essen.de/gnu-pascal/contrib/gpcasm.zip
Section 17.3 of the DJGPP FAQ discusses some methods to convert "Intel" syntax to "AT&T".
Tell me how to do DPMI, BIOS and other DOS related things. ==========================================================
DPMI, BIOS and other functions are no different than other system functions. Refer to section 3.1 how to access your system's C-library. This small example shows how to use DPMI, copying some structures and function prototypes of `<dpmi.h>':
--------------------------------------------------------- program DPMITest;
{$X+}
{ `Byte' is `unsigned char' in C, `ShortInt' is `short' in C, `MedCard' is `unsigned long' in C, `Word' is `unsigned' in C, etc. (all these types are built-in). }
type TDpmiVersionRet = record major : Byte; minor : Byte; flags : ShortInt; cpu : Byte; master_pic : Byte; slave_pic : Byte; end;
type TDpmiFreeMemInfo = record largest_available_free_block_in_bytes : MedCard; maximum_unlocked_page_allocation_in_pages : MedCard; maximum_locked_page_allocation_in_pages : MedCard; linear_address_space_size_in_pages : MedCard; total_number_of_unlocked_pages : MedCard; total_number_of_free_pages : MedCard; total_number_of_physical_pages : MedCard; free_linear_address_space_in_pages : MedCard; size_of_paging_file_partition_in_pages : MedCard; reserved1 : MedCard; reserved2 : MedCard; reserved3 : MedCard; end;
function DpmiGetVersion (var ret: TDpmiVersionRet): integer; asmname '__dpmi_get_version'; function DpmiGetFreeMemoryInformation (var info: TDpmiFreeMemInfo): integer; asmname '__dpmi_get_free_memory_information';
var version: TDpmiVersionRet; meminfo: TDpmiFreeMemInfo;
begin if DpmiGetVersion ( version ) = 0 then begin writeln('CPU type : ', version.cpu, '86'); writeln('DPMI major : ', version.major); writeln('DPMI minor : ', version.minor); end else writeln ( 'Error in DpmiGetVersion' ); if DpmiGetFreeMemoryInformation ( meminfo ) = 0 then writeln ( 'Free DPMI memory : ', meminfo.total_number_of_free_pages, ' pages.') else writeln ( 'Error in DpmiGetMemoryInformation' ); end. ---------------------------------------------------------
I'm accessing an `array[1..4000000] of byte' and I got an exception. ====================================================================
Per default, the maximum stack size of a djgpp application is 256K. If you need more, you have to adjust it with the stubedit program, i.e.:
stubedit your_app.exe minstack=5000K
Still, it might be a good idea to use pointers for this kind of structures, and allocate the memory at runtime.
5.0 (reserved) ***************
6.0 STRINGS ***********
What's this confusion about strings? ====================================
Turbo Pascal strings have a length byte in front. Since a byte has the range 0 .. 255, this limits a string to 255 characters. However, the Pascal string schema, as defined in section 6.4.3.3.3 of the ISO-10206: 1990 Extended Pascal standard, is a schema record:
type String (Capacity : Integer) = record Length : 0 .. Capacity; String : packed array [1 .. Capacity + 1] of Char end;
The `+ 1' is a GPC extension to make it feasible to automatically add the #0 terminator when passing or assigning them to CStrings. Thus at the expense of a little added complexity ( must declare capacity, don't use GetMem, and the additional space requirement ) you can now have very long strings.
The following Q&A is also about strings: ========================================
Q: Should the different variants in a variant record overlay in the same memory? Previous Pascals I have used have guaranteed this, and I've got low-level code that relies on this. The variants are not the same length, and they are intended not to be.
A: No, this is intentional so that the discriminants are not overwritten, and they can be properly initialized in the first place. Consider:
record case Boolean of False: (s1 : String (42)); True: (s2 : String (99)); end;
If the strings would overlay, in particular their discriminants would occupy the same place in memory. How should it be initialized? Either way, it would be wrong for at least one of the variants...
So, after a discussion in comp.lang.pascal.ansi-iso where this topic came up concerning file variables (which also require some automatic initialization and finalization), we decided to do this in GPC for all types with automatic initialization and finalization (currently files and schemata, in the future this might also be Delphi compatible classes and user-defined initialized and finalized types), since the standard does not guarantee variants to overlay, anyway...
There are two ways in GPC to get guaranteed overlaying (both non-standard, of course, since the standard does not assume anything about internal representations; both BP compatible), `absolute' declarations and variable type casts. E.g., in order to overlay a byte array to a variable v:
var b: array [1 .. SizeOf (v)] of Byte absolute v;
or
type t = array [1 .. SizeOf (v)] of Byte;
then `t (v)' can be used as a byte array overlayed to v.
Q: In standard Pascal you expect s[1] to align with the first character position of s and thus one character to the left is the length of s. Thus s[0] is the length of s. True?
A: This holds for UCSD/BP strings (which GPC does not yet implement, but that's planned). The only strings Standard Pascal knows are arrays of char without any length value.
Q: Two different kinds of strings with the same name - string - does make a bit of confusion. Perhaps the oldstyle strings could be renamed "short string" ?
A: When we implement the short strings, we'll have to do such a distinction. Our current planning goes like this:
string (n): string schema (EP compatible)
string [n]: short string (UCSD/BP compatible, where n must be <= 255)
string: dependent on flags, by default undiscriminated schema, but in BP mode (or with a special switch) short string of capacity 255 (UCSD/BP compatible). ---- Frank
Q: So when will these short strings be available?
A: It's been planned for over a year. The delay has been caused by more pressing problems.
What about C strings? =====================
A C string (`char *') is an array of char, terminated with a `NULL' char.
C library functions require C, not Pascal style string arguments. However, Pascal style strings are automatically converted to C style strings when passed to a routine that expects C style strings. This works only if the routine reads from the string, not if it modifies it.
E.g., this is how you access the `system()' call in your C library (which is not necessary any more, since `Execute' is already built-in):
--------------------------------------------------------- program SysCall;
function system(name : CString): integer; C;
var result : integer;
begin result := system ('ls -l'); writeln('system() call returned : ', result); end. ---------------------------------------------------------
There may be other ways to do the same thing; you could use a type `PChar' instead of `CString' and replace all references to `CString' with `PChar'. `PChar' is predefined now (though we recommend `CString' because it makes it clearer that we're talking about some kind of string rather than a single character), and a lot of library routines in Pascal for many applications (in the GPC unit and some other units) have been written (see above)...
type PChar = ^char;
Do *NOT* pass a "C" style string as a var-argument if the C prototype says `const char *' or you will get a coredump.
6.0 Getting Help ****************
If you have never submitted a bug report before there's a good HOWTO article on Freshmeat. The URL is
http://freshmeat.net/news/2000/02/26/951627540.html
Please read the documentation (info files, readme's and the file `BUGS') that come with GPC, plus other docs that might help (the DJGPP FAQ if you use DJGPP, etc.) before you send email to the maintainers or mailing list.
Help! The compiler crashed! ===========================
If the compiler crashes, you have discovered a bug. A reliable compiler never crashes. To help the maintainers fix this bug, it is important that you send us a problem report.
I think I found a bug - now what? =================================
Bugs are best reported to the GPC mailinglist gpc@gnu.de. That way, they always reach the maintainers. Try to give as much information as possible, plus a short code snippet that triggers the compiler bug. If you're on Unix, you can find out where the compiler crashed if you enable coredumps, then load the compiler (`gpc1') plus the core file in the debugger (`gdb /your_path_here/gpc1 core'), then type `backtrace' to get a stacktrace. Include this stacktrace in your bug report.
Which newsgroup(s) are suited for GPC related problems? =======================================================
There are several Pascal related newsgroups, but none is dedicated just to GNU Pascal. This one may be useful:
comp.lang.pascal.misc Pascal in general and ungrouped Pascals.
Pascal syntax related questions may be appropriate in:
comp.lang.pascal.ansi-iso Pascal according to ANSI and ISO standards.
The next newsgroup is a haven for beginners, answering questions that would apply to almost any pascal. However, if you have a GPC-specific question don't post there - use the GPC mailing list. And if in doubt use the GPC mailing list.
comp.lang.pascal.borland Borland Pascal questions.
Also, the mailing list archives are a good place to look. The URL is
http://www.gnu.de/archive/wilma.cgi/gpc
and
http://www.gnu.de/archive/wilma.cgi/gpc-announce
respectively. Now the pages also come in gpc signature colors. :-)
Note: Currently, the search option is working fine. If you find it broken, please email me at anja@drewitz.de. Please don't mail a copy to the GPC list because I let procmail move all mails with To: gpc... and Cc: gpc... to a separate folder and would not see your mail for a long time. --- Anja
How to post to the mailing list ===============================
You can send a message to the GPC mailing list by sending email to the list address gpc@gnu.de as if it were a person.
How to become a subscriber to the mailing list ==============================================
You can join the mailing list by sending a message to gpc-request@gnu.de (NOT gpc@gnu.de !) with your request to be added to the list of the form: subscribe your@mail.address
How to unsubscribe from the mailing list ========================================
To leave the mailing list, send a message to gpc-request@gnu.de of the form: unsubscribe your@mail.address
What other mailing lists may be of interest to me? ==================================================
There is a (low-traffic) announce list, gpc-announce@gnu.de, to stay up-to-date. To subscribe to the list, write an email with "subscribe gpc-announce" in the body to majordomo@gnu.de. (The subject will be ignored.)
7.0 Miscellaneous *****************
I want to contribute; where do I start? =======================================
If you want to contribute, please write to the mailing list.
Where is the GNU Pascal FTP site? WWW? ======================================
The master FTP site for GNU Pascal is `agnes.dida.physik.uni-essen.de'. GNU Pascal related files can be found in:
http://agnes.dida.physik.uni-essen.de/~gnu-pascal ftp://agnes.dida.physik.uni-essen.de/gnu-pascal
A not quite up-to-date mirror is:
ftp://sunsite.doc.ic.ac.uk/gnu/MORE_GNU/gnu-pascal/
The latest developer releases can be downloaded from:
ftp://agnes.dida.physik.uni-essen.de/gnu-pascal/
GPC To-Do list, latest features, fixed bugs:
http://agnes.dida.physik.uni-essen.de/~gnu-pascal/todo.html
Also, we have a homepage on the web:
http://home.pages.de/~GNU-Pascal/
---Frank Heckenbach, frank@g-n-u.de, http://fjf.gnu.de/
For now, this same page appears at
http://agnes.dida.physik.uni-essen.de/~gnu-pascal/
About this FAQ. ===============
Original Maintainer: J.J. van der Heijden j.j.vanderheijden@student.utwente.nl
Current Maintainer: Russ Whitaker russwhit@mind.net
This is the second incarnation of the GNU Pascal FAQ list. Comments about, suggestions for, or corrections to this FAQ list are welcome.
Please make sure to include in your mail the version number of the document to which your comments apply (you can find the version at the beginning of this FAQ list).
Many people have contributed to this FAQ, only some of them are acknowledged above. Much of the info in, and inspiration for this FAQ list was taken from the gpc mailing list traffic, so you may have (unbeknownst to you) contributed to this list.