General information
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What is Free Pascal (FPC)?
Originally named FPK-Pascal, the Free Pascal compiler is a 32 and 64 bit Turbo Pascal and Delphi compatible Pascal compiler for DOS, Linux, Win32, OS/2, FreeBSD, AmigaOS, Mac OS X, Mac OS classic and several other platforms (the number of supported targets grows all the time, although not all of them are on the same level as the main ones).
The Free Pascal compiler is available for several architectures: x86, Sparc (v8,v9), ARM, x86_64 (AMD64/Opteron), PowerPC and PowerPC64. An older version (the 1.0 series) and current development version also support m68k, the current development version also supports MIPS (in both big endian and little endian modes).
The compiler is written in Pascal and is able to compile its own sources. The source files are under GPL and included.
Short history:
- 06/1993: project start
- 10/1993: first little programs work
- 03/1995: the compiler compiles the own sources
- 03/1996: released to the internet
- 07/2000: 1.0 version
- 12/2000: 1.0.4 version
- 04/2002: 1.0.6 version
- 07/2003: 1.0.10 version
- 05/2005: 2.0.0 version
- 12/2005: 2.0.2 version
- 08/2006: 2.0.4 version
- 09/2007: 2.2.0 version
- 08/2008: 2.2.2 version
- 04/2009: 2.2.4 version
- 12/2009: 2.4.0 version
- 11/2010: 2.4.2 version
- 05/2011: 2.4.4 version
- 01/2012: 2.6.0 version
- 12/2012: 2.6.2 version
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Which versions exist, and which one should I use?
The latest official version is 2.6.2, the first fixes release in the 2.6.x series. New development is performed in 2.7.x series, which eventually gets released as 2.8.0 or 3.0.0, depending on milestones achieved.
Historic versions
FPC's version numbering changed a few times over the years. Pre 1.0 versioning moved to the Wiki 1.0 versioning article.
Modern versioning
Together with the release of 1.0 the version numbering was slightly changed, and a system in versioning resembling the Linux kernels has been introduced.
- Releases that only fix bugs in version 1.0 are numbered 1.0.x.
- Post 1.0 development (the so called snapshots) have version number 1.1.x.
- Eventually the 1.1.x versions, when stabilized were released as the 2.0.x series, preceded by betas marked as 1.9.x. Fixes on 2.0 release were numbered 2.0.x, fixes on 2.2 release 2.2.x, fixes on the 2.4 release as 2.4.x etc
- The new development after the 2.4.0 release is numbered 2.5.x and so on.
- Repackagings that affect sources are indicated with a single letter as suffix (e.g. 2.0.4a), this is usually the case for platforms that weren't part of the original release round.
- The stable branch (fixes_2_4) always has an odd last number (2.4.1, 2.4.3). Compilers with such versions are snapshots, and e.g. a snapshot with 2.4.1 can be anywhere between 2.4.0 and the moment 2.4.2 branched off (may 2010). Likewise the fixes_2_4 branch will hold version 2.4.3 till 2.4.4 is branched off (typically two months before its release). After 2.4.4 the stable branch's number is updated to 2.4.5 etc.
Normally you would want to use a release. Releases are considered stable, and easier to support (the bugs, quirks and unintended "features" are well known after a period of time, and workarounds exist).
Development snapshots (which are generated daily) reflect the current status of the compiler. Development versions probably have new features and larger bugs fixed since the last release, but might have some temporary stability drawbacks (which are usually fixed by the next day).
Development snapshots are often quite useful for certain categories of users. Ask in the maillists if it is worth the trouble in your case if you're not sure.
Snapshots of the stable branch (fixes_2_6) are meant to test release engineering. They are mainly interesting in the months before a release to extensively test the branch from which the release is created.
We advise all users to upgrade to the newest version for their target (preferably the new stable 2.6.x series).
A graphical timeline of the FPC project plus its near future would be:
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Free Pascal and GNU Pascal - a comparison
- Aim:
- Free Pascal tries to implement a Borland compatible pascal compiler on as many platforms as possible. GNU Pascal tries to implement a portable pascal compiler based on POSIX.
- Version:
- Currently, Free Pascal is at version 2.6.2 (December 2012). GNU Pascal is at version 2.1 (from 2002, which can be built with several different GCC's as backend; their Mac OS X version is an exception though, as it follows the GCC version number).
- Tracking:
- Between releases, development versions of FPC are available through daily snapshots and the source via SVN. GPC issues a set of patches to the last version a few times a year, and there are regular snapshot for OS X and Windows, made by users.
- Operating systems:
- Free Pascal runs on a large amount of platforms of OSes, e.g. DOS, Win32 (no Unix porting layer needed), Linux, FreeBSD, NetBSD, OS/2, BeOS, Classic Mac OS, Mac OS X, and AmigaOS, on, at the moment the following architectures: x86, x86_64 (AMD64), Sparc, PowerPC, PowerPC64, ARM, Motorola m68k (m68k only in version 1.0.x and the latest development versions) and MIPS (both big endian and little endian mode available in the latest development versions). GNU Pascal runs basically on any system that can run GNU C, and for which the buildprocess was verified.
- Bootstrapping:
- FPC requires a suitable set of binutils (AS,AR,LD) on some platforms, gmake and a commandline compiler. New architectures/OSes are crosscompiled. GPC bootstraps via a suitable version of GCC, and requires a full set of binutils, flex, bison, gmake, a POSIX shell and libtool
- Sources:
- Free Pascal is entirely written in Pascal (about 6 MB of source code), while GNU Pascal is written in C (it's an adaptation of the GNU C compiler: 2.8 MB code + 8 MB of GNU C code)
- Language:
- Free Pascal supports the Borland Pascal dialect, implements the Delphi Object Pascal language and has some Mac Pascal extensions. GNU Pascal supports ISO 7185, ISO 10206, (most of) Borland Pascal 7.0
- Extensions:
- Free Pascal implements method, function and operator overloading (later Delphi versions add these, so strictly not an extension anymore) GNU Pascal implements operator overloading.
- License:
- Both compilers come under the GNU GPL.
- Author:
- Free Pascal was started by Florian Klämpfl, Germany (florian@freepascal.org), GNU Pascal was started by Jukka Virtanen, Finland (jtv@hut.fi).
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License and copyright information
Applications created by the compiler and using the runtime library come under a modified library gnu public license (LGPL), which permit no restriction on the type of license the application has. It is therefore possible to create closed source or proprietary software using Free Pascal.
This extra exception to the LGPL is added:
As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you not obligated to do so. If you do not wish to do so, delete this exception statement from your version. Please note that you still have to comply to the LGPL, which, for example, requires you to provide the source code of the runtime library. If you want to write proprietary closed source software, please do this to comply:- Most people can satisfy the source code requirement by mentioning the rtl source code can be downloaded at the Free Pascal web site: if you did not modify the rtl this is considered adequate to satisfy the LGPL requirement of providing source code.
- If you made modifications to the runtime library, you cannot keep them for yourself, you must make them available if requested.
- Distribute the LGPL license with your product.
The compiler source code, on the other hand, comes under the GNU Public license, which means that any usage of the compiler source can only be used in software projects which have the same license.
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Getting the compiler
The latest official stable Free Pascal release is available for download from all official mirrors
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Free Pascal installation hints
- Do not install the compiler in a directory which contains spaces in its name, since some of the compiler tools do not like these
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Why do i have to supply a user name and password to get Free Pascal ?
You are trying to login in to an ftp site. You must use the login name: anonymous and as your password, you should put your e-mail address.
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Access denied error when connecting to the Free Pascal FTP site
The Free Pascal main ftp site can only accept a maximum number of simultaneous connections. If this error occurs, it is because this limit has been reached. The solution is either to wait and retry later, or better still use one of the Free Pascal mirror sites.
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I want a new version NOW
In the time between the release of new official versions, you can have a look at and test developer versions (so-called "snapshots"). Be warned though: this is work under progress, so in addition to old bugs fixed and new features added, this may also contain new bugs.
Snapshots are generated automatically each night from the current source at that moment. Sometimes this may fail due to bigger changes not yet fully implemented. If your version doesn't work, try again one or two days later.
The latest snapshot can always be downloaded from the development web page.
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Installing a snapshot
To install a snapshot, extract the zip archive into the existing program directory of the last official version of Free Pascal (after making a backup of the original of course). You can also extract it into an empty directory and then move the files to the program directory, overwriting existing files.
Make sure that you extract the ZIP archive such that the included directory structure remains intact. For example if you use PKUNZIP, use "pkunzip -d" instead of just "pkunzip" (InfoZIP unzip doesn't require any special parameters). Note that snapshots also contain a new RTL which most likely can't be used with the previous release version, so backup your old RTL as well.
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I have to write a program for homework. Can you help?
No. Please, don't send us mail about homework, we are no teachers. The Free Pascal development team tries to give good support for the Free Pascal compiler and are trying to always reply to emails. If we get emails like this, this becomes harder and harder.
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How do I make a real Windows application with windows and menu bars?
The easiest way is to download Lazarus. It won't be just a Windows application, it will also work under Linux, FreeBSD and Mac OS X. -
How do I make a game with Free Pascal? Can I make a game like Doom 3?
Yes, you can make games with Free Pascal and if you are really good you can make a game like Doom 3. Making games is difficult, you need to be an experienced programmer to make them. The web site www.pascalgamedevelopment.com is a community of people who program games in Free Pascal and Delphi.If you want a start, please start to study JEDI-SDL or PTCPas. Also you can try to study an existing game, for example The Sheep Killer is a very simple game and it should not be very hard to understand its code.
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Getting more information when an application crashes
- The easiest possibility is to recompile your program with -gl debugging option. This way unit LineInfo is automatically linked in, and the printout after a program crash then contains source line numbers in addition to addresses of the crash. To see runtime library (RTL) functions in the backtrace with their real name, you have to recompile the RTL with -gl too.
- For more comprehensive checking, compile the program with debugging information (use the -g command line option)
- Load the program in the debugger
gdb(pas)(w) --directory=<src dirs> myprog.exe
Notes:- Under UNIX systems (Linux, the BSD's), don't add the ".exe" after myprog
- "src dirs" is a list of directories containing the source code files of myprog and the units it uses seperated by semi-colons (";"). The current directory is automatically included.
- Once inside the debugger, you can (optionally) set the command line options that will be passed to your program using the command "set args <option1 option2 ...>"
- To start the program, type "run" and press enter
- After the program has crashed, the address of the instruction where the crash occurred will be shown. The debugger will try to display the source code line corresponding with this address. Note that this can be inside a procedure of the RTL, so the source may not always be available and most likely the RTL wasn't compiled with debugging information.
- If you then type "bt" (BackTrace), the addreses in the
call stack will be shown (the addresses of the procedures which were
called before the program got to the current address). You can see
which source code lines these present using the command
info line *<address>
For example:info line *0x05bd8
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Increasing the heap size
By default Free Pascal allocates a small part of RAM for your application as heap memory. If it just allocated all it could get, people running Windows would have problems as Windows would increase the swap file size to give the program more memory on and on, until the swap file drive would be full.
You can specify the size of the heap with -Chxxxx.
However, the heap size doesn't really matter, since the Heap is able to grow: if you've used all the available heap space, the program will try to get more memory from the Operating system (OS), so the heap is limited to the maximum amount of free memory provided by the OS.
It is only handy if you know you will need at least a certain amount of memory. You can then specify this value using the -Ch parameter, so your program will allocate it at once on startup. This is slightly faster than growing the heap a number of times.
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Compiler seems to skip files in directories that -Fu points to
This sometimes happens with installation/compilation scripts if the copying command doesn't preserve dates. The object files get older than the PPU file, and the compiler tries to recompile them. A simple touch will solve it.
Also note that FPC, contrary to Turbo Pascal keeps track of includefiles. Modified includefiles or duplicate names might trigger an attempt at recompiling
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Why are the generated binaries so big?
There are several reasons and remedies for this:- You can create smartlinked applications. To turn on the generation of smartlinkable units, use the -Cx command line option when compiling your units. To turn on the linking of previously generated smarlinkable units, use the -XX (-XS in 0.99.12 and earlier) command line option when compiling a program.
- Normally, all symbol information is included in the resulting program (for easier debugging). You can remove this by using the -Xs command line option when compiling your program (it won't do anything when compiling units)
- You can use UPX to pack the .EXEs (just like e.g. pklite) for Dos (GO32v2) and Windows targets. Look here for more info.
- You can use LXLITE for packing EMX binaries, but you won't be able to run them under DOS (with extender) any more then. This issue is not relevant for native OS/2 binaries compiled for target OS2 with version 1.9.x and above, because these don't run under DOS anyway. In addition, it might not be possible to use compressed binaries on lower OS/2 versions (like 2.x) depending on chosen type of compression. LXLITE can be found e.g. on Hobbes, search for LXLITE.
- Turn on optimalisations, both for supplied packages (RTL, FV, FCL) and for your own code, this will also decrease the code size.
- Keep in mind that under Windows NT/2k/XP/Vista, compressed binaries startup relatively slow. Test under various conditions (OS, CPU speed, memory) if the behaviour is acceptable before compressing
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Configuration file problems (fpc.cfg or ppc386.cfg)
Starting from version 1.0.6 of Free Pascal, the configuration file is called fpc.cfg instead of ppc386.cfg. For backward compatibility , ppc386.cfg is still searched first and, if found, is used instead of fpc.cfg.
Since 1.0.6 is now over 5 years old, the ppc386.cfg support will be phased out. 2.2.2 will warn, and 2.4.0+ will no longer search ppc386.cfg
Versions prior to Free Pascal 1.0.6 do not recognize fpc.cfg, so if you wish to use an earlier version of the compiler using the same configuration file used with FPC version 1.0.6 (or later), the configuration file should be renamed to ppc386.cfg.
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Runtime errors
When there is abnormal termination of an application generated by Free Pascal, it is very probable that a runtime error will be generated. These errors have the form :
Runtime error 201 at $00010F86 $00010F86 main, line 7 of testr.pas $0000206DThe 201 in this case indicates the runtime error number. The definition of the different runtime error numbers is described in the Free Pascal user's manual, Appendix D. The hexadecimal numbers represent the call stack when the error occured.
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Standard units
To see the list of base units supplied with Free Pascal, and on which platform they are supported, consult the Free Pascal user's manual. There is also a short description of what each unit does in the same section of the manual.
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Debugging smartlinked code does not fully work
Debugging smart linked code might not work correctly. This is due to the fact that no type information is emitted for smartlinked code. If this would not be done, the files would become enormous.
While debugging, it is not recommended to use the smartlinking option.
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Debugging shared library (dynamic linked library) code does not fully work
Debugging shared libraries (or dynamic linked libraries) produced by the Free Pascal compiler is not officially supported.
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PPU files binary compatibility between versions
Can't compile a program using a binary only version of a unit
Sometimes, even though there is a binary version of a module (unit file and object file) available, the compiler still gives compilation errors. This can be caused either by an incompatibility in the PPU file format (which should change only between major versions of the compiler), or by a change in one of the units of the RTL which has changed in between releases.
To get more information, compile the code using the -va (show all information) compiler switch, and the unit loading phase will be displayed. You might discover that the unit being loaded requires to be recompiled because one of the unit it uses has changed.
So if you plan on distributing a module without the source code, the binaries should be compiled and made available for all versions of the compiler you wish to support, otherwise compilation errors are bound to occur.
In other words, the unit (PPU) file format does not change significantly in between minor releases of the compiler (for exemple : from 1.0.4 and 1.0.6) which means they are binary compatible, but because the interface of the units of the RTL certainly changes between versions, recompilation will be required for each version anyways.
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Will you support ISO Extended Pascal?
FPC's primary goal is to be a Turbo Pascal and Delphi-compatible compiler, and it also supports a subset of the Mac-Pascal dialect. All of these are incompatible to some extent with the ISO Standard and Extended Pascal languages. While in theory it would be possible to add a separate ISO Standard or Extended Pascal mode, until now no people interested in such functionality have stepped up to work on such features.GNU-Pascal is however a modern compiler that can compile ISO Extended Pascal. If you have any need for the ISO Extended Pascal dialect, we recommend you to take a look at this compiler.
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What about .NET?
Occasionally, users ask about a FPC that supports .NET, or our plans in that direction.Mainly the users are either interested because of .NET's portability aspects (Mono is quoted over and over again), or because it is supposed to be the next big thing in Windows programming, and they think windows programming won't be possible in the future.
While the FPC core developpers are somewhat interested out of academic curiousity (mainly because it could be a pilot for a generalized backend creating bytecode) there are however several problems with .NET in combination with FPC:
- Pascal is a language that uses pointers, and existing codebases can only be unmanaged. Unmanaged code is not portable under .NET, so that already kills most possible benefits. This also means that existing FPC and Delphi code won't run on .NET. There are more such little language problems.
- FPC's libraries don't base on .NET classes and datamodels (and can't be changed to do so without effectively rewriting them), moreover the libraries could only be unmanaged too, or they would be incompatible
- There is nothing practical known yet about how portable an average .NET program will be. Little experiments with hello world level code mean nothing, that kind of code works with nearly any language. A good test would be to see existing non trivial codebases run unmodified under mono, that were not designed with mono in mind. Just like we try to do for Delphi
- The fact that on Windows 80% of the .NET code seems to be ASP.NET doesn't help either. This makes porting existing code less useful (since ASP.NET is tied to IIS), and new codebases of portable code can be set in nearly every language
- Operating System dependant code wouldn't work anymore, since the win32 interface is unmanaged.
So effectively this means that for FPC to benefit from .NET you would have to significantly adapt the language (thus compiler) and libraries, and be incompatible with the existing native sourcecode. This is not adding support for .NET in FPC, but reimplementing FPC on .NET from near scratch without backwards compatibility. Moreover that also means that existing apps would have to be rewritten for .NET, since it would take more than a simple recompile with a FPC/.NET compiler.
While unmanaged code has some uses (allows to integrate with managed code inside windows easier), this still needs a codegenerator backend to be written, interfaces and libraries defined, for little practical use. This means a lot of work and since .NET take up is not really high, this might not be worth it, since an unmanaged FPC/.NET would only be minimally used.
However if a FPC user does the bulk of the work (e.g. a bytecode codegenerator, and maybe some base libraries) and if the work is suitable for inclusion in FPC (a very big if), we will of course include it.
Since support for generating JVM bytecode has been added to the compiler, such a project may be more realistic now than it has been in the past. Many of the caveats mentioned above still hold though: language compatibility is not 100% and most standard units will have to be reimplemented.
Pascal language related information
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Considerations in porting to other processors
Because the compiler now supports processors other than the Intel, it is important to take a few precautions so that your code will execute correctly on all processors.
- Limit your use of asm statements unless it is time critical code
- Try not to rely on the endian of the specific machines when doing
arithmetic operations. Furthermore, reading and writing of binary data
to/from files will probably require byte swaps across different endian
machines (swap is your friend in this case). This is even more
important if you write binary data to files. Freepascal defines
ENDIAN_LITTLEorENDIAN_BIGto indicate the target endian. - Try limiting your local variables in subroutines to 32K, as this is the limit of some processors, use dynamic allocation instead.
- Try limiting the size of parameters passed to subroutines to 32K, as this is the limit of some processors, use const or var parameters instead.
- The CPU32 or CPU64 (defined by FPC starting from version 1.9.3) are defined indicating if the target is a 32-bit or 64-bit cpu; This can help you separate 32-bit and 64-bit specific code.
- Use the ptruint type (defined by FPC starting from version 1.9.3) when declaring an ordinal that will store a pointer, since pointers can be either 32-bit or 64-bit depending on the processor and operating system.
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Considerations in porting code to other operating systems
Because the compiler supports several different operating systems, is important to take a few precautions so that your code will execute correctly on all systems.
- File sharing is implemented differently on different operating systems, so opening already opened files may fail on some operating systems (such as Windows). The only correct way to make sure to have the same file sharing behavior is to use the I/O routines furnished in sysutils.
- Clean up at the end of your program, i.e. close all files on exit, and release all allocated heap memory, as some operating systems don't like it when some things are left allocated or opened.
- Some operating systems limit the local stack space which can be allocated, therefore it is important to limit subroutine nesting, and the amount of local variables. Limiting total stack space usage at a given moment to at most 256 KBytes while make porting easier.
- Do not hard code paths to files, try to use relative paths instead
- Use the following constants (defined in the system unit)
to get information on files, line endings, and to build paths:
- LineEnding : Indicates the characters which end a text line
- LFNSupport : Indicates if long filenames are supported (more then 8.3 characters)
- DirectorySeparator : The character or characters which separate path components
- DriveSeparator : The character which separate the drive specification from the rest of the path
- PathSeparator : The character which separates directories in the search path environment
- FileNameCaseSensitive : Boolean indicating if the filenames for this system are case-sensitive or not
- AllFilesMask : String containing a wildcard expression for all files
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Compiling Delphi code using Free Pascal
The compiler supports the Delphi classes. Make sure you use the -S2 or -Sd switches (see the manuals for the meaning of these switches). For a list of Delphi incompatibilities also check the manual.
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Building a unit
It works like in Turbo Pascal. The first keyword in the file must be UNIT (not case sensitive). The compiler will generate two files: XXX.PPU and XXX.O. The PPU file contains the interface information for the compiler and the O-file the machine code (an object file, whose precise structure depends on the assembler you used). To use this unit in another unit or program, you must include its name in the USES clause of your program.
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Compiling the system unit
To recompile the system unit, it is recommended to have GNU make installed. typing 'make' in the rtl source directory will then recompile all RTL units including the system unit. You may choose to descend into the directory of your OS (e.g. rtl/go32v2) and do a 'make' there.
It is possible to do all this manually, but you need more detailed knowledge of the RTL tree structure for that.
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How does procedure overloading work?
Here is a procedure overloading example:
procedure a(i : integer); begin end; procedure a(s : string); begin end; begin a('asdfdasf'); a(1234); end.You must be careful. If one of your overloaded functions is in the interface part of your unit, then all overloaded functions must be in the interface part. If you leave one out, the compiler will complain with a 'This overloaded function can't be local' message. Overloaded functions must differ in their parameters, it's not enough if their return types are different.
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Calling C functions
It is possible to call functions coded in C, which were compiled with the GNU C compiler (GCC). For calling the C function strcmp declare the following:
function strcmp(s1 : pchar;s2 : pchar) : integer;cdecl;external;
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Integrated Assembler syntax
The default assembler syntax (AT&T style) is different from the one in Borland Pascal (Intel style).
However, as of version 0.99.0, the compiler supports Intel style assembly syntax. See the documentation for more info on how to use different assembler styles.
Since version 1.9.2, the compiler also uses the register calling convention, which means the compiler can assemble assembler routines in Delphi source code without modification.
Since version 1.9.8, the register calling convention is default for Delphi mode.
A description of the AT&T syntax can be found in the GNU Assembler documentation.
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Unit system not found errors
System (syslinux - not the bootloader, sysos2 or syswin32, depending on platform) is Pascal's base unit which is implicitely used in all programs. This unit defines several standard procedures and structures, and must be found to be able to compile any pascal program by FPC.
The location of the system.ppu and syslinux.o files are determined by the -Fu switch which can be specified commandline, but is usually in the ppc386.cfg or fpc.cfg configuration file.
If the compiler can't find this unit there are three possible causes:
- The ppc386.cfg or fpc.cfg isn't in the same path as the compiler executable (go32v2, win32 and OS/2) or can't be found as "/etc/fpc.cfg" or ".fpc.cfg" in your homedirectory (Linux).
- The fpc.cfg or ppc386.cfg doesn't contain the -Fu line, or a wrong one. See the build faq (PDF), especially the chapters about the fpc.cfg and the directory structure.
- The files ARE found but the wrong version or platform. Correct ppc386.cfg or fpc.cfg to point to the right versions or reinstall the right versions (this can happen if you try to use a snapshot compiler while the -Fu statement in the used fpc.cfg still points to the RTL that came with the official release compiler).
A handy trick can be executing "ppc386 programname -vt", this shows where the compiler is currently looking for the system unit's files. You might want to pipe this through more (Dos, OS/2, Windows) or less (Linux), since it can generate more than one screen information:
Dos, OS/2, Windows: ppc386 programname -vt |more
unix, linux: ppc386 programname -vt |less
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There is a new extension that will be really useful. Will you include it?
Occasionally somebody asks for a new extension on the maillist, and the discussions that follow have a recurring pattern. An extension is quite a big deal for the FPC team, and there are some criteria that are used to select if an extension is "worth" the trouble. The most important pre-selection criteria are:- Compatibility must not be compromised in any way. Existing codebases on at least the Pascal level must keep running. This is often more difficult than most people think.
- The extension must have real value. Anything that is only a shorter notation does not apply, unless it is out of compatibility with an existing Pascal/Delphi codebase. Practically it means it must make something possible that can't be done otherwise or be a compatibility item
- The change must fit in with the scope of the project, implementing a Pascal compiler which can have a RAD and generic DB system. This excludes features like inline SQL, and large garbage collected objectframeworks.
- Explanation of the feature
- Why it is needed, what does it make possible?
- How you would implement it?
- Lots of examples of typical use, and tests for possible problem cases
Besides these pre-selection rules and documentation, the other important question is who is going to do the work. Keep in mind that the FPC devels are volunteers with to-do lists that are booked till the next decade. You can't simply expect they'll drop everything from their hands and implement the feature because you need it urgently, or think it is nice. If you are not willing to implement it yourself, and submit patches, chances are slim. Remarks as "this will attract a lot of users because" are considered with a lot of scepsis, since that applies to any new development.
Runtime library related information
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Using the graph unit with Free Pascal
Since version 1.0, we have a completely platform independent way of selecting resolutions and bitdepths. You are strongly encouraged to use it, because other ways will probably fail on one or other platform. See the documentation of the graph unit for more information.
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Why do I get wrong colours when using the graph unit?
If you use detect as graphdriver, you will end up with the highest supported bitdepth. Since the graph unit currently only supports up to 16 bits per pixel modes and since this bitdepth is supported by all graphics cards made in at least the last 5 years, you will most likely get a 16 bit mode.
The main problem is that in 16 (and 15, 24, 32, ...) bit modes, the colors aren't set anymore using an index in a palette (the palettized way is called "indexed color"). In these modes, the color number itself determines what color you get on screen and you can't change this color. The color is encoded as follows (for most graphics cards on PC's at least):
- 15 bit color: lower 5 bits are blue intensity, next come 5 bits of green and then 5 bits of red. The highest bit of the word is ignored.
- 16 bit color: lower 5 bits are blue intensite, next come *6* bits of green and then 5 bits of red.
This means that either you have to rewrite your program so it can work with this so-called "direct color" scheme, or that you have to use D8BIT as graphdriver and DetectMode as graphmode. This will ensure that you end up with a 256 (indexed) color mode. If there are no 256 color modes supported, then graphresult will contain the value GrNotDetected after you called InitGraph and you can retry with graphdriver D4BIT. Make sure you use the constant names (D8BIT, D4BIT, ...) and not their actual numeric values, because those values can change with the next release! That is the very reason why such symbolic constants exist.
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File sharing and file locks
The standard runtime library file I/O routines open files in the default sharing mode of the operating system (system, objects units). Because of this, you might get problems if the file is opened more than once either by another process or the same process.
Generally the behaviors for the different operating systems are as follows :
- UNIX systems : There is no verification at all.
- Windows : An access denied error will be reported.
- Amiga : An access denied error will be reported.
- DOS / OS/2 : If the file is opened more than once by the same process, no errors will occur, otherwise an access denied error will be reported.
There are two ways to solve this problem:
- Use specific operating system calls (such as file locking on UNIX and Amiga systems) to get the correct behavior.
- Use the sysutils unit or the Free Component Library TFileStream File I/O routines, which try to simulate, as much as possible, file sharing mechanisms.
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File denied errors when opening files with reset
Trying to open files using
reseton non-text files might cause a Runtime Error 5 (Access denied).All files opened using the above system unit routine use the current
filemodevalue to determine how the file is opened. By default,filemodeis set to 2 (Read/Write access).So, a call to
reseton non-text files does not indicate that the file will be opened read-only. So, trying to open a file usingresetwith the defaults will fail on read-only files.filemodeshould be set to 0 (Real-only access) before callingresetto solve this problem. A sample solution is shown below.const { possible values for filemode } READ_ONLY = 0; WRITE_ONLY = 1; READ_WRITE = 2; var oldfilemode : byte; f: file; begin assign(f,'myfile.txt'); oldfilemode := filemode; { reset will open read-only } filemode := READ_ONLY; reset(f,1); { restore file mode value } filemode := oldfilemode; // ... close(f); end.For more information, consult the Free Pascal reference manual
DOS related information
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Releasing software generated by the DOS compiler
- If your program uses floating point code (which is very probable), make sure to read "Applications created with Free Pascal crash on 80386 systems" regarding special issues which might occur. Math coprocessor emulation software is then required (wmemu387.dxe should be redistributed with your software)
- The target system must have a DPMI server. To avoid problems, the file cwsdpmi.exe should always be redistributed with your application
- The target system must have DOS 3.3 or later
- The default heap size is 2 Megabytes. Automatic growing of the heap is supported
- The default stack size is 256 Kbytes. See also "Changing the default stack size"
- The stack checking option is available on this platform.
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Debugging
The GNU debugger v4.16 and later have been tested, and generally work as they should. Because the GNU debugger is C oriented, some pascal types might not be represented as they should. It is suggested to use the text mode IDE instead of GDB, which is available for the DOS target.
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Dynamic Libraries
Creation or use of shared libraries (also called dynamic link libraries) is not supported under this platform.
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Profiling
Profiling with gprof is supported for this platform.
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Running Free Pascal without a math coprocessor?
On the Intel version the emulator is automatically loaded by the compiler if you add the following commands to your autoexec.bat:
SET 387=N SET EMU387=C:\PP\BIN\GO32V2\WEMU387.DXE(don't forget to replace the C:\PP with the directory where you installed FPC) -
Applications created with Free Pascal crash on 80386 systems
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Trying to run an application which does floating point operations on a 386 system without a math co-processor will crash unless the emu387 unit is used, as this unit loads the math co-processor emulator (called wmemu387.dxe). You can add the unit as follows:
program myprog; uses emu387, ...When the application is released, the software package should also include the wmemu387.dxe redistributable file to avoid problems. .
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Some 80386 systems have a hardware bug which corrupt the accumulator register EAX if it is used in a MOV instruction just after a POPAL instruction. Prior to version 1.0.5, the compiler and runtime library could generate such code sequences. This is now fixed and should no longer cause problems
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The mouse cursor is not visible in graphics screens
A lot of DOS mouse drivers don't support mouse cursors in VESA modes properly. Logitech is said to have a decent mouse driver, which can be found here
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Accessing I/O ports
With versions before 0.99.10: if you're under DOS you can use the outport* and inport* procedures of the go32 unit.
Since version 0.99.8, the Port array is supported like in TP, as long as you use the ports unit in your program (not available under Win32).
I/O port access is possible under Linux, but that requires root privileges. Check the manuals for the IOPerm, ReadPort and WritePort procedures. (Unit Linux)
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Accessing DOS memory / Doing graphics programming
You can do like in Turbo Pascal, via absolute or mem[]. For larger memory blocks use the dosmemput/dosmemget routines in the Go32 unit.
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Changing the default stack size
Under the DOS (GO32V2) target, the default stack size to 256 bKbytes. This can be modified with a special DJGPP utility called stubedit. It is to note that the stack may also be changed with some compiler switches, this stack size, if greater then the default stack size will be used instead, otherwise the default stack size is used.
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Using OS/2 generated applications under DOS
OS/2 applications (including the compiler) created with version 1.0.x and before should work correctly under vanilla DOS, since they are based on EMX (versions prior to 1.0.5 had big problems with EMX under DOS, this is now fixed). It is important to note that the compiled applications require the EMX runtime files (emx.exe) to execute properly. It may be necessary to distribute these files with the generated application.
Binaries created for target OS2 with version 1.9.x and above cannot run under DOS any more, because they directly use OS/2 API functions not available when running under extender - you need to compile for a newly added EMX target which provides this capability of running on both platforms.
Windows related information
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Releasing software generated by the windows compiler
There is no special requirements for releasing software for the windows platform, it will work directly out of the box. The following are default for the Windows platform:
- The default heap size is 256 Kbytes. Automatic growing of the heap is supported. It is to note that Windows 95, Windows 98 and Windows Me limit the heap to 256 Mbytes (this is a limitation of those Operating systems, not of Free Pascal, consult MSDN article Q198959 for more information).
- Stack size is unlimited
- The stack checking option is not available on this platform.
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Debugging
The GNU debugger v4.16 and later have been tested, and generally work as they should. Because the GNU debugger is C oriented, some pascal types might not be represented as they should. It is suggested to use the text mode IDE instead of GDB, which is available for windows targets.
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Dynamic libraries
Creation and use of shared libraries (also called dynamic link libraries) is fully supported by the compiler. Refer to the Programmer's Reference Manual for more information on shared library creation and use.
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Profiling
Profiling is supported using gprof, starting with version 1.0.7. It requires mingw to be installed, and that fpc.cfg point to the correct library paths.
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Graph and problems with keyboard, mouse and "dummy dos windows"
Problem:
- If you use the Graph unit under Win32, you can't use the API mouse unit for mouse support or use the win32 Crt unit to get keyboard data. The reason for this is that the window popped up is a GUI window, and not a console one.
- Use units WinMouse and WinCrt instead.
Problem:
- When you follow the above advice, and you run your purely Graph based win32 program from the RUN menu in windows, a dummy dos window is opened.
- Set the application type to GUI:
{$apptype GUI}and put this line before your programs InitGraph statement:ShowWindow(GetActiveWindow,0);This will hide the dos window window.
Some of the demos (like fpctris) use these techniques
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Cygwin binary directory in your path sometimes causes strange problems
The mingw make tool seems to look for a "sh.exe", which it finds when the cygwin binary directory is in the path. The way directories are searched changes, and the build process dies.
Solution: don't put cygwin in your global path for now, only add it when needed. Efforts are made to work around this.
Possible untested workaround: add mingw sh.exe to a directory before the cygwin binary directory in the path
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Using the DOS compiler under Windows 95
There is a problem with the DOS (GO32V2) compiler and Windows 95 on computers with less than 16 Megabytes of RAM. First set in the properties of the DOS box the DPMI memory size to max value. Now try to start a demo program in the DOS box, e.g. HELLO (starting may take some time). If this works you will be able to get the compiler to work by recompiling it with a smaller heap size, perhaps 2 or 4 MB (option -Chxxxx).
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Using OS/2 generated applications under Windows
Normally OS/2 applications (including the compiler) created with version 1.0.x and before should work under Windows, since they are based on EMX - see note about running OS/2 applications under DOS for more detailed information. You need the RSX extender (rsx.exe) to do this. There have been problems reported while trying to run EMX applications under NT / 2000 / XP systems though. This seems to be a problem with EMX (RSX) itself. It is not recommended to use Free Pascal OS/2 compiled programs under NT / 2000 and XP, as it might produce unexpected results.
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Using DOS generated applications under windows
Several problems have been found running DOS software under certain versions of Windows (NT / 2000 / XP). These seem to be problems with the DOS emulation layers (emulated DPMI services or the Go32 extender). These problems may not occur with all software generated by FPC. Either applications should be tested on these systems before being released, or Windows versions should be generated instead.
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The mouse cursor does not respond in the Windows IDE
In windowed mode, the mouse cursor might not respond to mouse moves and clicks. Just change the properties of the console, and remove the quick edit mode option. This should solve the mouse response problems.
UNIX related information
This section also applies to most unix variants, such as linux, freebsd and netbsd.
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Releasing software generated by the unix compilers
- The default heap size is 256 Kbytes for the intel version, and 128 Kb for the m68k versions. Automatic growing of the heap is supported.
- There is no stack space usage limit.
- Under Solaris and QNX, stack checking is simulated.
- Minimal operating system versions :
- Linux : Kernel v2.4.x or later.
- FreeBSD : version 5.x or later. (4.x can be made to work with minor work)
- NetBSD : version 1.5 or later.
- Solaris : version 5.7 of SunOS or later (should work with earlier versions, but untested).
- Qnx : version 6.1.0 or later (should work with earlier versions, but untested).
- Mac OS X : version 10.3.9 or later
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Debugging
The GNU debugger v4.16 and later have been tested, and generally work as they should. Because the GNU debugger is C oriented, some pascal types might not be represented as they should. For FreeBSD a recent GDB (v5) SVN snapshot is recommended for Pascal support and ease of building
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Dynamic libraries
These operating systems do support shared libraries (also called dynamic link libraries), Free Pascal currently does not emit position independant code (PIC), as required for the creation of shared libraries.
Therefore, even though the linux compiler target permits creating shared libraries, the usage of that shared library may result in undefined behavior, especially if accessing global variables in the library. Creation of shared libraries is not recommended with the current version of the compiler.
Importing code from shared libraries does work as expected though, since it does not require usage of position independant code.
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Profiling
Profiling is supported using gprof under linux, FreeBSD and NetBSD, the latter two only since 1.0.8. On other other unix-like operating systems, profiling is currently not supported.
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Libc is missing on platforms other than Linux/i386
Libc is a Kylix compatibility unit. Because it contains many i386 specific code and features structures from legacy kernels, it has not been made available on other platforms.
To access Unix functionality, please use units like baseunix and unix.
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Why can't the linker find "vga"?
This error typically looks like this:
Free Pascal Compiler version 2.2.x [xxxx/yy/zz] for i386 Copyright (c) 1993-2008 by Florian Klaempfl Target OS: Linux for i386 Compiling test.pp Assembling test Linking test /usr/bin/ld: cannot find -lvga test.pp(6,4) Warning: Error while linking Closing script ppas.sh 5 Lines compiled, 0.2 secThis error is not an error in the installation of FPC or FPC itself, but a missing Svgalib library in your unix install. Please install the required library using your favourite package manager tool
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Compiler indicates missing as and ld
Normally unix systems have the assembler (as) and linker (ld) pre-installed and already in the search path. That is the reason why these tools are not supplied with the compiler.
If the compiler cannot find these tools, either they are not in your search path, or they are not installed. You should either add the path where the tools are located to your search path, and / or you should install these tools.
It is to note that the Solaris version of FPC contains these tools.
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An error occurred while linking, or "did you forget -T?"
There is a bug in GNU LD 2.19 and 2.19.1 that causes it to crash when processing FPC-generated linker scripts. This bug has been fixed in the mean time.
At the same time, LD has been modified to emit a warning of the form
/usr/bin/ld: warning: link.res contains output sections; did you forget -T?This warning is benign, and FPC intentionally does not pass -T to LD. The reason is that if -T is used, LD's internal linker script is ignored and only FPC's linker script is used. Such linker scripts also contain paths to libraries however, and if we would ignore the internal linker script then LD would no longer find libraries in distribution-specific directories.
OS/2 related information
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Releasing software generated by the OS/2 compiler
The OS/2 compiler version 1.0.x and before is based on EMX, therefore it should work both on OS/2 and on vanilla DOS systems. In version 1.9.x and above this functionality is preserved in newly added target EMX, whereas binaries for target OS2 can only run under real OS/2. The following notes apply to OS2 target in 1.0.x and EMX in 1.9.x and above:
- All applications generated for the OS/2 (EMX) target require the EMX 0.9d (or later) runtime files to run. These files should be redistributed with your software. All the files which should be redistributed are included in emxrt.zip
- Under OS/2, LIBPATH should be modified to add the EMX DLL paths. Otherwise, programs will not run and will abort with an error 'Cannot find EMX.dll'.
- The default heap size is 256 Kbytes. Automatic growing of the heap is supported.
- Stack can grow up to 256 Kbytes by default. This can be changed by the user or developper using the emxstack or emxbind utilities.
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Debugging
The GNU debugger v4.16 (EMX port) has been tested (including its PM add-on, pmgdb.exe) and generally works as it should. Because the GNU debugger is C oriented, some pascal types might not be represented correctly.
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Dynamic libraries
Even though this operating system permits the creation and usage of shared libraries (also called dynamic link libraries), the compiler currently only permits importing routines from dynamic libraries (creation of dynamic libraries is unsupported).
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Profiling
Profiling is currently not supported for this platform.
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Using DOS generated applications under OS/2
It has been reported that some DOS (GO32V2) applications (including the DOS compiler itself) generated by the compiler fail on some OS/2 installations. This is due to problems in the OS/2 DPMI server.
You should use native OS/2 applications under OS/2 (including the native OS/2 compiler) or try installing a new OS/2 fixpack to see if it solves the problem.
INSTALL.EXE of version 1.0.6 or below fails with an unknown error (-1) under OS/2
or
INSTALL.EXE of version 1.0.6 or above complains about missing TZ variable under OS/2
You are most probably using an older version of OS/2 (like OS/2 Warp 3.0) and don't have TZ variable in your environment. The easiest solution is to add "SET TZ=..." (e.g. "SET TZ=CET-1CEST,3,-1,0,7200,10,-1,0,10800,3600" for most of western and central Europe) line to your CONFIG.SYS, and restart OS/2. The proper setting for you can be found e.g. using the TZCALC tool from TIME868 package.
OS/2 compiler not working after upgrading to 1.9.6 or newer
An updated version of GNU assembler (as.exe) is packaged with release 1.9.6 (newer version was necessary to get support for features of modern CPUs). This version of the GNU tool was created with Innotek port of GNU C and relies on its libc. This results in higher limitations regarding supported configurations, because this libc needs recent version of OS/2 Unicode support libraries (LIBUNI.DLL and UCONV.DLL) not available in base OS/2 Warp 3.0 and OS/2 Warp 4.0. The updated versions were distributed by IBM in corrective packages (fixpaks) - see e.g. WarpUpdates site for information about OS/2 fixpaks and links for downloading them. This issue isn't valid for WarpServer for e-Business, MCP and eComStation - these already have the correct version.
Compilation under OS/2 fails with error "Can't call the assembler"
Apart from the point mentioned above, there is at least one more potential reason for issues with executing the assembler and resulting in error message "Can't call the assembler, error 2 switching to external assembling". This error may be result of the OS/2 system not being able to find DLLs required for the assembler. Make sure that you installed FPC completely (these DLLs are part of file asldos2.zip) and that you have set LIBPATH according to instructions in README.TXT (and restarted afterwards). If in doubts, running the assembler directly from the command line (e.g. "as --version" to show the installed as.exe version) may be helpful to see name of the missing dynamic library or other details about the problem.
BeOS related information
The BeOS port is current no longer maintained-
Releasing software generated by the BeOS compiler
Software generated for the BeOS target will only work on the intel based version of BeOS.
- The target system must have at least BeOS v4.0 or later (BeOS 5.1d 'Dano' is not supported)
- The default heap size is 256 Kbytes. Automatic growing of the heap is supported
- Stack size is set to 256 Kbytes. This cannot be changed
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Debugging
This operating system uses DWARF debugging information, and Free Pascal does not support emitting DWARF debugging information. It is currently impossible to debug applications under BeOS
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Dynamic libraries
Even though this operating system permits the creation and usage of shared libraries (also called dynamic link libraries), the compiler currently only permits importing routines from dynamic libraries (creation of dynamic libraries is unsupported).
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Profiling
Profiling is currently not supported for this platform.
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BeOS Linking problems
It has been reported that certain versions of the linker that shipped with some versions of BeOS are broken. If you get an error when linking fpc applications, try updating your version of ld from the following site.
Amiga related information
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Releasing software generated by the Amiga compiler
- The target system must have AmigaOS v2.04 or higher
- The default heap size is 128 Kbytes. Automatic growing of the heap is supported.
- Stack size is not set by the compiler, but by the stack command on the CLI. Because of this, and because default stack sizes for this target are small, it is recommended to always compile software with stack checking enabled.
- By default, the compiler generates code for the 68020+ processor. The code generated will not work on 68000 and 68010 systems unless the -O0 compiler switch is used, and there is no runtime checking. It is up to you to implement CPU verification at program startup. The standard runtime libraries have been compiled for the 68000 target, and should not cause any problems.
- All floating point operations are simulated, and use the single floating point type. You will need to recompile all standard runtime libraries and your application, with the software floating point option off, if you wish to use hardware floating point.
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Debugging
Source level debugging is not supported for the Amiga target. Assembler target debugging is possible though, using the excellent Barfly debugger.
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Dynamic libraries
Even though this operating system permits the creation and usage of shared libraries (also called dynamic link libraries), the compiler does not support either the importing or creation of shared libraries. Importing must be done manually in assembler.
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Profiling
Profiling is currently not supported for this platform.