Subsections

- 1 Local directives
  - 1 `$A` or `$ALIGN` : Align Data
  - 2 `$ASMMODE` : Assembler mode (Intel 80x86 only)
  - 3 `$B` or `$BOOLEVAL` : Complete boolean evaluation
  - 4 `$C` or `$ASSERTIONS` : Assertion support
  - 5 `$DEFINE` : Define a symbol
  - 6 `$ELSE` : Switch conditional compilation
  - 7 `$ENDIF` : End conditional compilation
  - 8 `$ERROR` : Generate error message
  - 9 `$F` : Far or near functions
  - 10 `$FATAL` : Generate fatal error message
  - 11 `$GOTO` : Support `Goto` and `Label`
  - 12 `$H` or `$LONGSTRINGS` : Use AnsiStrings
  - 13 `$HINT` : Generate hint message
  - 14 `$HINTS` : Emit hints
  - 15 `$IF` : Start conditional compilation
  - 16 `$IFDEF Name` : Start conditional compilation
  - 17 `$IFNDEF` : Start conditional compilation
  - 18 `$IFOPT` : Start conditional compilation
  - 19 `$INFO` : Generate info message
  - 20 `$INLINE` : Allow inline code.
  - 21 `$I` or `$IOCHECKS` : Input/Output checking
  - 22 `$I` or `$INCLUDE` : Include file
  - 23 `$I` or `$INCLUDE` : Include compiler info
  - 24 `$I386_XXX` : Specify assembler format (Intel 80x86 only)
  - 25 `$L` or `$LINK` : Link object file
  - 26 `$LINKLIB` : Link to a library
  - 27 `$M` or `$TYPEINFO` : Generate type info
  - 28 `$MACRO` : Allow use of macros.
  - 29 `$MAXFPUREGISTERS` : Maximum number of FPU registers for variables (Intel 80x86 only)
  - 30 `$MESSAGE` : Generate info message
  - 31 `$MMX` : Intel MMX support (Intel 80x86 only)
  - 32 `$NOTE` : Generate note message
  - 33 `$NOTES` : Emit notes
  - 34 `$OUTPUT_FORMAT` : Specify the output format
  - 35 `$P` or `$OPENSTRINGS` : Use open strings
  - 36 `$PACKENUM` : Minimum enumeration type size
  - 37 `$PACKRECORDS` : Alignment of record elements
  - 38 `$Q` `$OVERFLOWCHECKS`: Overflow checking
  - 39 `$R` or `$RANGECHECKS` : Range checking
  - 40 `$SATURATION` : Saturation operations (Intel 80x86 only)
  - 41 `$SMARTLINK` : Use smartlinking
  - 42 `$STATIC` : Allow use of `Static` keyword.
  - 43 `$STOP` : Generate fatal error message
  - 44 `$T` or `$TYPEDADDRESS` : Typed address operator (@)
  - 45 `$UNDEF` : Undefine a symbol
  - 46 `$V` or `$VARSTRINGCHECKS` : Var-string checking
  - 47 `$WAIT` : Wait for enter key press
  - 48 `$WARNING` : Generate warning message
  - 49 `$WARNINGS` : Emit warnings
  - 50 `$X` or `$EXTENDEDSYNTAX` : Extended syntax
- 2 Global directives
  - 1 `$APPTYPE` : Specify type of application (Win32 and AmigaOS only)
  - 2 `$D` or `$DEBUGINFO` : Debugging symbols
  - 3 `$DESCRIPTION` : Application description
  - 4 `$E` : Emulation of coprocessor
  - 5 `$G` : Generate 80286 code
  - 6 `$INCLUDEPATH` : Specify include path.
  - 7 `$L` or `$LOCALSYMBOLS` : Local symbol information
  - 8 `$LIBRARYPATH` : Specify library path.
  - 9 `$M` or `$MEMORY` : Memory sizes
  - 10 `$MODE` : Set compiler compatibility mode
  - 11 `$N` : Numeric processing
  - 12 `$O` : Overlay code generation
  - 13 `$OBJECTPATH` : Specify object path.
  - 14 `$S` : Stack checking
  - 15 `$UNITPATH` : Specify unit path.
  - 16 `$W` or `$STACKFRAMES` : Generate stackframes
  - 17 `$Y` or `$REFERENCEINFO` : Insert Browser information

#
1 Compiler directives

Free Pascal supports compiler directives in the source file. They are not the same as Turbo Pascal directives, although some are supported for compatibility. There is a distinction between local and global directives; local directives take effect from the moment they are encountered, global directives have an effect on all of the compiled code.

Many switches have a long form also. If they do, then the name of the long form is given also. For long switches, the + or - character to switch the option on or off, may be replaced by `ON` or `OFF` keywords.

Thus `{$I+}` is equivalent to `{$IOCHECKS ON}` or `{$IOCHECKS +}` and `{$C-}` is equivalent to `{$ASSERTIONS OFF}` or `{$ASSERTIONS -}`

The long forms of the switches are the same as their Delphi counterparts.

#
1 Local directives

Local directives can occur more than once in a unit or program, If they have a command-line counterpart, the command-line argument is restored as the default for each compiled file. The local directives influence the compiler's behaviour from the moment they're encountered until the moment another switch annihilates their behaviour, or the end of the current unit or program is reached.

## 1 `$A` or `$ALIGN` : Align Data

This switch is recognized for Turbo Pascal Compatibility, but is not yet implemented. The alignment of data will be different in any case.

##
2 `$ASMMODE` : Assembler mode (Intel 80x86 only)

The `{$ASMMODE XXX}` directive informs the compiler what kind of assembler it can expect in an `asm` block. The `XXX` should be replaced by one of the following:

att
  Indicates that `asm` blocks contain AT&T syntax assembler.
intel
  Indicates that `asm` blocks contain Intel syntax assembler.
direct
  Tells the compiler that asm blocks should be copied directly to the assembler file.

These switches are local, and retain their value to the end of the unit that is compiled, unless they are replaced by another directive of the same type. The command-line switch that corresponds to this switch is `-R`.

The default assembler reader is the AT&T reader.

## 3 `$B` or `$BOOLEVAL` : Complete boolean evaluation

This switch is understood by the Free Pascal compiler, but is ignored. The compiler always uses shortcut evaluation, i.e. the evaluation of a boolean expression is stopped once the result of the total exression is known with certainty.

So, in the following example, the function `Bofu`, which has a boolean result, will never get called.

    If False and Bofu then
      ...

This has as a consequence that any additional actions that are done by `Bofu` are not executed.

## 4 `$C` or `$ASSERTIONS` : Assertion support

The `{$ASSERTION}` switch determines if assert statements are compiled into the binary or not. If the switch is on, the statement

    Assert(BooleanExpression,AssertMessage);

Will be compiled in the binary. If te `BooleanExpression` evaluates to `False`, the RTL will check if the `AssertErrorProc` is set. If it is set, it will be called with as parameters the `AssertMessage` message, the name of the file, the LineNumber and the address. If it is not set, a runtime error 227 is generated.

The `AssertErrorProc` is defined as

    Type
      TAssertErrorProc=procedure(const msg,fname:string;lineno,erroraddr:longint);
    Var
      AssertErrorProc = TAssertErrorProc;

This can be used mainly for debugging purposes. The system unit sets the `AssertErrorProc` to a handler that displays a message on `stderr` and simply exits. The sysutils unit catches the run-time error 227 and raises an `EAssertionFailed` exception.

## 5 `$DEFINE` : Define a symbol

The directive

    {$DEFINE name}

defines the symbol `name`. This symbol remains defined until the end of the current module (i.e. unit or program), or until a `$UNDEF name` directive is encountered.

If `name` is already defined, this has no effect. `Name` is case insensitive.

The symbols that are defined in a unit, are not saved in the unit file, so they are also not exported from a unit.

## 6 `$ELSE` : Switch conditional compilation

The `{$ELSE}` switches between compiling and ignoring the source text delimited by the preceding `{$IFxxx}` and following `{$ENDIF}`. Any text after the `ELSE` keyword but before the brace is ignored:

    {$ELSE some ignored text}

is the same as

    {$ELSE}

This is useful for indication what switch is meant.

## 7 `$ENDIF` : End conditional compilation

The `{$ENDIF}` directive ends the conditional compilation initiated by the last `{$IFxxx}` directive. Any text after the `ENDIF` keyword but before the closing brace is ignored:

    {$ENDIF some ignored text}

is the same as

    {$ENDIF}

This is useful for indication what switch is meant to be ended.

## 8 `$ERROR` : Generate error message

The following code

    {$ERROR This code is erroneous !}

will display an error message when the compiler encounters it, and increase the error count of the compiler. The compiler will continue to compile, but no code will be emitted.

## 9 `$F` : Far or near functions

This directive is recognized for compatibility with Turbo Pascal. Under the 32-bit and 64-bit programming models, the concept of near and far calls have no meaning, hence the directive is ignored. A warning is printed to the screen, as a reminder.

As an example, the following piece of code:

    {$F+}

    Procedure TestProc;

    begin
     Writeln ('Hello From TestProc');
    end;

    begin
     testProc
    end.

Generates the following compiler output:

    malpertuus: >pp -vw testf
    Compiler: ppc386
    Units are searched in: /home/michael;/usr/bin/;/usr/lib/ppc/0.9.1/linuxunits
    Target OS: Linux
    Compiling testf.pp
    testf.pp(1) Warning: illegal compiler switch
    7739 kB free
    Calling assembler...
    Assembled...
    Calling linker...
    12 lines compiled,
     1.00000000000000E+0000

One can see that the verbosity level was set to display warnings.

When declaring a function as `Far` (this has the same effect as setting it between `{$F+} ...{$F-}` directives), the compiler also generates a warning:

    testf.pp(3) Warning: FAR ignored

The same story is true for procedures declared as `Near`. The warning displayed in that case is:

    testf.pp(3) Warning: NEAR ignored

## 10 `$FATAL` : Generate fatal error message

The following code

    {$FATAL This code is erroneous !}

will display an error message when the compiler encounters it, and the compiler will immediatly stop the compilation process.

This is mainly useful inc conjunction wih `{$IFDEF}` or `{$IFOPT}` statements.

## 11 `$GOTO` : Support `Goto` and `Label`

If `{$GOTO ON}` is specified, the compiler will support `Goto` statements and `Label` declarations. By default, `$GOTO OFF` is assumed. This directive corresponds to the `-Sg` command-line option.

As an example, the following code can be compiled:

    {$GOTO ON}

    label Theend;

    begin
      If ParamCount=0 then
        GoTo TheEnd;
      Writeln ('You specified command-line options');
    TheEnd:
    end.

Remark: When compiling assembler code using the inline assembler readers, any labels used in the assembler code must be declared, and the `{$GOTO ON}` directive should be used.

## 12 `$H` or `$LONGSTRINGS` : Use AnsiStrings

If `{$LONGSTRINGS ON}` is specified, the keyword `String` (no length specifier) will be treated as `AnsiString`, and the compiler will treat the corresponding variable as an ansistring, and will generate corresponding code.

By default, the use of ansistrings is off, corresponding to `{$H-}`. The system unit is compiled without ansistrings, all its functions accept shortstring arguments. The same is true for all RTL units, except the sysutils unit, which is compiled with ansistrings.

## 13 `$HINT` : Generate hint message

If the generation of hints is turned on, through the `-vh` command-line option or the `{$HINTS ON}` directive, then

    {$Hint This code should be optimized }

will display a hint message when the compiler encounters it.

By default, no hints are generated.

## 14 `$HINTS` : Emit hints

`{$HINTS ON}` switches the generation of hints on. `{$HINTS OFF}` switches the generation of hints off. Contrary to the command-line option `-vh` this is a local switch, this is useful for checking parts of the code.

## 15 `$IF` : Start conditional compilation

The directive `{$IF expr}` will continue the compilation if the boolean expression `expr` evaluates to `true`. If the compilation evaluates to false, then the source is skipped to the first `{$ELSE}` or `{$ENDIF}` directive.

The compiler must be able to evaluate the expression at parse time. This means that variables or constants that are defined in the source cannot be used. Macros and symbols may be used, however.

More information on this can be found in the section about conditionals.

## 16 `$IFDEF Name` : Start conditional compilation

If the symbol `Name` is not defined then the `{$IFDEF name}` will skip the compilation of the text that follows it to the first `{$ELSE}` or `{$ENDIF}` directive. If `Name` is defined, then compilation continues as if the directive wasn't there.

## 17 `$IFNDEF` : Start conditional compilation

If the symbol `Name` is defined then the `{$IFNDEF name}` will skip the compilation of the text that follows it to the first `{$ELSE}` or `{$ENDIF}` directive. If it is not defined, then compilation continues as if the directive wasn't there.

## 18 `$IFOPT` : Start conditional compilation

The `{$IFOPT switch}` will compile the text that follows it if the switch `switch` is currently in the specified state. If it isn't in the specified state, then compilation continues after the corresponding `{$ELSE}` or `{$ENDIF}` directive.

As an example:

    {$IFOPT M+}
      Writeln ('Compiled with type information');
    {$ENDIF}

Will compile the writeln statement if generation of type information is on.

Remark: The `{$IFOPT}` directive accepts only short options, i.e. `{$IFOPT TYPEINFO}` will not be accepted.

## 19 `$INFO` : Generate info message

If the generation of info is turned on, through the `-vi` command-line option, then

    {$INFO This was coded on a rainy day by Bugs Bunny}

will display an info message when the compiler encounters it.

This is useful in conjunction with the `{$IFDEF}` directive, to show information about which part of the code is being compiled.

## 20 `$INLINE` : Allow inline code.

The `{$INLINE ON}` directive tells the compiler that the `Inline` procedure modifier should be allowed. Procedures that are declared inline are copied to the places where they are called. This has the effect that there is no actual procedure call, the code of the procedure is just copied to where the procedure is needed, this results in faster execution speed if the function or procedure is used a lot.

By default, `Inline` procedures are not allowed. This directive must be specified to use inlined code. The directive is equivalent to the command-line switch `-Si`. For more information on inline routines, consult the Reference guide.

## 21 `$I` or `$IOCHECKS` : Input/Output checking

The `{$I-}` or `{$IOCHECKS OFF}` directive tells the compiler not to generate input/output checking code in the program. By default, the compiler does not generate this code, it must be switched on using the `-Ci` command-line switch.

When compiling using the `-Ci` compiler switch, the Free Pascal compiler inserts input/output checking code after every input/output call in the code. If an error occurred during input or output, then a run-time error will be generated. Use this switch to avoid this behaviour.

To check if something went wrong, the `IOResult` function can be used to see if everything went without problems.

Conversely, `{$I+}` will turn error-checking back on, until another directive is encountered which turns it off again.

The most common use for this switch is to check if the opening of a file went without problems, as in the following piece of code:

    assign (f,'file.txt');
    {$I-}
    rewrite (f);
    {$I+}
    if IOResult<>0 then
      begin
      Writeln ('Error opening file: "file.txt"');
      exit
      end;

See the `IOResult` function explanation in Reference guide for a detailed description of the possible errors that can occur when using input/output checking.

## 22 `$I` or `$INCLUDE` : Include file

The `{$I filename}` or `{$INCLUDE filename}` directive tells the compiler to read further statements from the file `filename`. The statements read there will be inserted as if they occurred in the current file.

The compiler will append the .pp extension to the file if no extension is given. Do not put the filename between quotes, as they will be regarded as part of the file's name.

Include files can be nested, but not infinitely deep. The number of files is restricted to the number of file descriptors available to the Free Pascal compiler.

Contrary to Turbo Pascal, include files can cross blocks. I.e. a block can start in one file (with a `Begin` keyword) and can end in another (with a `End` keyword). The smallest entity in an include file must be a token, i.e. an identifier, keyword or operator.

The compiler will look for the file to include in the following places:

1. It will look in the path specified in the include file name.
2. It will look in the directory where the current source file is.
3. it will look in all directories specified in the include file search path.

Directories can be added to the include file search path with the `-I` command-line option.

## 23 `$I` or `$INCLUDE` : Include compiler info

In this form:

    {$INCLUDE %xxx%}

where `xxx` is one of `TIME`, `DATE`, `FPCVERSION` or `FPCTARGET`, will generate a macro with the value of these things. If `xxx` is none of the above, then it is assumed to be the value of an environment variable. It's value will be fetched, and inserted in the code as if it were a string.

For example, the following program

    Program InfoDemo;

    Const User = {$I %USER%};

    begin
      Write ('This program was compiled at ',{$I %TIME%});
      Writeln (' on ',{$I %DATE%});
      Writeln ('By ',User);
      Writeln ('Compiler version: ',{$I %FPCVERSION%});
      Writeln ('Target CPU: ',{$I %FPCTARGET%});
    end.

Creates the following output:

    This program was compiled at 17:40:18 on 1998/09/09
    By michael
    Compiler version: 0.99.7
    Target CPU: i386

## 24 `$I386_XXX` : Specify assembler format (Intel 80x86 only)

This switch selects the assembler reader. `{$I386_XXX}` has the same effect as `{$ASMMODE XXX}`, section AsmReader

This switch is deprecated, the `{$ASMMODE XXX}` directive should be used instead.

## 25 `$L` or `$LINK` : Link object file

The `{$L filename}` or `{$LINK filename}` directive tells the compiler that the file filename should be linked to the program. This cannot be used for libraries, see section section linklib for that.

The compiler will look for this file in the following way:

1. It will look in the path specified in the object file name.
2. It will look in the directory where the current source file is.
3. it will look in all directories specified in the object file search path.

Directories can be added to the object file search path with the `-Fo` option.

On LINUX systems and on operating systems with case-sensitive filesystems (such as UNIX systems), the name is case sensitive, and must be typed exactly as it appears on your system.

Remark: Take care that the object file you're linking is in a format the linker understands. Which format this is, depends on the platform you're on. Typing `ld` or `ld -help` on the command line gives a list of formats `ld` knows about.

Other files and options can be passed to the linker using the `-k` command-line option. More than one of these options can be used, and they will be passed to the linker, in the order that they were specified on the command line, just before the names of the object files that must be linked.

##
26 `$LINKLIB` : Link to a library

The `{$LINKLIB name}` will link to a library name. This has the effect of passing `-lname` to the linker.

As an example, consider the following unit:

    unit getlen;

    interface
    {$LINKLIB c}

    function strlen (P : pchar) : longint;cdecl;

    implementation

    function strlen (P : pchar) : longint;cdecl;external;

    end.

If one would issue the command

    ppc386 foo.pp

where foo.pp has the above unit in its `uses` clause, then the compiler would link the program to the c library, by passing the linker the `-lc` option.

The same effect could be obtained by removing the linklib directive in the above unit, and specify `-k-lc` on the command-line:

    ppc386 -k-lc foo.pp

## 27 `$M` or `$TYPEINFO` : Generate type info

For classes that are compiled in the `{$M+}` or `{$TYPEINFO ON}` state, the compiler will generate Run-Time Type Information (RTTI). All descendent objects of an object that was compiled in the `{$M+}` state will get RTTI information too, as well as any published classes. By default, no Run-Time Type Information is generated. The `TPersistent` object that is present in the FCL (Free Component Library) is generated in the `{$M+}` state. The generation of RTTI allows programmers to stream objects, and to access published properties of objects, without knowing the actual class of the object.

The run-time type information is accessible through the `TypInfo` unit, which is part of the Free Pascal Run-Time Library.

Remark: The streaming system implemented by Free Pascal requires that all streamable components be descendent from `TPersistent`.

## 28 `$MACRO` : Allow use of macros.

In the `{$MACRO ON}` state, the compiler allows to use C-style (although not as elaborate) macros. Macros provide a means for simple text substitution. More information on using macros can be found in the section Macros section. This directive is equivalent to the command-line switch `-Sm`.

By default, macros are not allowed.

## 29 `$MAXFPUREGISTERS` : Maximum number of FPU registers for variables (Intel 80x86 only)

The `{$MAXFPUREGISTERS XXX}` directive tells the compiler how much floating point variables can be kept in the floating point processor registers. This switch is ignored unless the `-Or` (use register variables) optimization is used.

This is quite tricky because the Intel FPU stack is limited to 8 entries. The compiler uses a heuristic algorithm to determine how much variables should be put onto the stack: in leaf procedures it is limited to 3 and in non leaf procedures to 1. But in case of a deep call tree or, even worse, a recursive procedure this can still lead to a FPU stack overflow, so the user can tell the compiler how much (floating point) variables should be kept in registers.

The directive accepts the following arguments:

N
  where `N` is the maximum number of FPU registers to use. Currently this can be in the range 0 to 7.
Normal
  restores the heuristic and standard behavior.
Default
  restores the heuristic and standard behaviour.

Remark: This directive is valid until the end of the current procedure.

## 30 `$MESSAGE` : Generate info message

If the generation of info is turned on, through the `-vi` command-line option, then

    {$MESSAGE This was coded on a rainy day by Bugs Bunny }

will display an info message when the compiler encounters it. The effect is the same as the `{$INFO}` directive.

## 31 `$MMX` : Intel MMX support (Intel 80x86 only)

Free Pascal supports optimization for the MMX Intel processor (see also chapter ).

This optimizes certain code parts for the MMX Intel processor, thus greatly improving speed. The speed is noticed mostly when moving large amounts of data. Things that change are

- Data with a size that is a multiple of 8 bytes is moved using the `movq` assembler instruction, which moves 8 bytes at a time

Remark: MMX support is NOT emulated on non-MMX systems, i.e. if the processor doesn't have the MMX extensions, the MMX optimizations cannot be used.

When MMX support is on, it is not allowed to do floating point arithmetic. It is allowed to move floating point data, but no arithmetic can be done. If floating point math must be done anyway, first MMX support must be switched off and the FPU must be cleared using the `emms` function of the cpu unit.

The following example will make this more clear:

    Program MMXDemo;

    uses mmx;

    var
       d1 : double;
       a : array[0..10000] of double;
       i : longint;

    begin
       d1:=1.0;
    {$mmx+}
       { floating point data is used, but we do _no_ arithmetic }
       for i:=0 to 10000 do
         a[i]:=d2;  { this is done with 64 bit moves }
    {$mmx-}
       emms;   { clear fpu }
       { now we can do floating point arithmetic }
       ...
    end.

See, however, the chapter on MMX () for more information on this topic.

## 32 `$NOTE` : Generate note message

If the generation of notes is turned on, through the `-vn` command-line option or the `{$NOTES ON}` directive, then

    {$NOTE Ask Santa Claus to look at this code}

will display a note message when the compiler encounters it.

## 33 `$NOTES` : Emit notes

`{$NOTES ON}` switches the generation of notes on. `{$NOTES OFF}` switches the generation of notes off. Contrary to the command-line option `-vn` this is a local switch, this is useful for checking parts of the code.

By default, `{$NOTES}` is off.

## 34 `$OUTPUT_FORMAT` : Specify the output format

`{$OUTPUT_FORMAT format}` has the same functionality as the `-A` command-line option: it tells the compiler what kind of object file must be generated. You can specify this switch only before the `Program` or `Unit` clause in your source file. The different kinds of formats are shown in table (Formats) .

The default output format depends on the platform the compiler was compiled on.

Table: Formats generated by the x86 compiler
Switch value | Generated format
AS | AT&T assembler file.
AS_AOUT | Go32v1 assembler file.
ASW | AT&T Win32 assembler file.
COFF | Go32v2 COFF object file.
MASM | Masm assembler file.
NASM | Nasm assembler file.
NASMCOFF | Nasm assembler file (COFF format).
NASMELF | Nasm assembler file (ELF format).
PECOFF | PECOFF object file (Win32).
TASM | Tasm assembler file.

## 35 `$P` or `$OPENSTRINGS` : Use open strings

If this switch is on, all function or procedure parameters of type string are considered to be open string parameters; this parameter only has effect for short strings, not for ansistrings.

When using openstrings, the declared type of the string can be different from the type of string that is actually passed, even for strings that are passed by reference. The declared size of the string passed can be examined with the `High(P)` call.

Default the use of openstrings is off.

## 36 `$PACKENUM` : Minimum enumeration type size

This directive tells the compiler the minimum number of bytes it should use when storing enumerated types. It is of the following form:

    {$PACKENUM xxx}
    {$MINENUMSIZE xxx}

Where the form with `$MINENUMSIZE` is for Delphi compatibility. `xxx` can be one of `1,2` or `4`, or `NORMAL` or `DEFAULT`.

As an alternative form one can use `{$Z1}`, `{$Z2}` `{$Z4}`. Contrary to Delphi, the default is (`{$Z4}`).

So the following code

    {$PACKENUM 1}
    Type
      Days = (monday, tuesday, wednesday, thursday, friday,
              saturday, sunday);

will use 1 byte to store a variable of type `Days`, whereas it nomally would use 4 bytes. The above code is equivalent to

    {$Z1}
    Type
      Days = (monday, tuesday, wednesday, thursday, friday,
              saturday, sunday);

## 37 `$PACKRECORDS` : Alignment of record elements

This directive controls the byte alignment of the elements in a record, object or class type definition.

It is of the following form:

    {$PACKRECORDS n}

Where `n` is one of 1, 2, 4, 16, `C`, `NORMAL` or `DEFAULT`. This means that the elements of a record that have size greater than `n` will be aligned on `n` byte boundaries. Elements with size less than or equal to `n` will be aligned to a natural boundary, i.e. to a power of two that is equal to or larger than the element's size. The type `C` is used to specify alignment as by the GNU CC compiler. It should be used only when making import units for C routines.

The default alignment (which can be selected with `DEFAULT`) is 2, contrary to Turbo Pascal, where it is 1.

More information on this and an example program can be found in the reference guide, in the section about record types.

## 38 `$Q` `$OVERFLOWCHECKS`: Overflow checking

The `{$Q+}` or `{$OVERFLOWCHECKS ON}` directive turns on integer overflow checking. This means that the compiler inserts code to check for overflow when doing computations with integers. When an overflow occurs, the run-time library will print a message `Overflow at xxx`, and exit the program with exit code 215.

Remark: Overflow checking behaviour is not the same as in Turbo Pascal since all arithmetic operations are done via 32-bit or 64-bit values. Furthermore, the `Inc()` and `Dec` standard system procedures are checked for overflow in Free Pascal, while in Turbo Pascal they are not.

Using the `{$Q-}` switch switches off the overflow checking code generation.

The generation of overflow checking code can also be controlled using the `-Co` command line compiler option (see Users' guide).

## 39 `$R` or `$RANGECHECKS` : Range checking

By default, the compiler doesn't generate code to check the ranges of array indices, enumeration types, subrange types, etc. Specifying the `{$R+}` switch tells the computer to generate code to check these indices. If, at run-time, an index or enumeration type is specified that is out of the declared range of the compiler, then a run-time error is generated, and the program exits with exit code 201. This can happen when doing a typecast (implicit or explicit) on an enumeration type or subrange type.

The `{$RANGECHECKS OFF}` switch tells the compiler not to generate range checking code. This may result in faulty program behaviour, but no run-time errors will be generated.

Remark: The standard functions `val` and `Read` will also check ranges when the call is compiled in `{$R+}` mode.

## 40 `$SATURATION` : Saturation operations (Intel 80x86 only)

This works only on the intel compiler, and MMX support must be on (`{$MMX +}`) for this to have any effect. See the section on saturation support (section SaturationSupport) for more information on the effect of this directive.

## 41 `$SMARTLINK` : Use smartlinking

A unit that is compiled in the `{$SMARTLINK ON}` state will be compiled in such a way that it can be used for smartlinking. This means that the unit is chopped in logical pieces: each procedure is put in it's own object file, and all object files are put together in a big archive. When using such a unit, only the pieces of code that you really need or call, will be linked in your program, thus reducing the size of your executable substantially.

Beware: using smartlinked units slows down the compilation process, because a separate object file must be created for each procedure. If you have units with many functions and procedures, this can be a time consuming process, even more so if you use an external assembler (the assembler is called to assemble each procedure or function code block separately).

The smartlinking directive should be specified before the unit declaration part:

    {$SMARTLINK ON}

    Unit MyUnit;

    Interface
     ...

This directive is equivalent to the `-Cx` command-line switch.

## 42 `$STATIC` : Allow use of `Static` keyword.

If you specify the `{$STATIC ON}` directive, then `Static` methods are allowed for objects. `Static` objects methods do not require a `Self` variable. They are equivalent to `Class` methods for classes. By default, `Static` methods are not allowed. Class methods are always allowed.

By default, the address operator returns an untyped pointer.

This directive is equivalent to the `-St` command-line option.

## 43 `$STOP` : Generate fatal error message

The following code

    {$STOP This code is erroneous !}

will display an error message when the compiler encounters it. The compiler will immediatly stop the compilation process.

It has the same effect as the `{$FATAL}` directive.

## 44 `$T` or `$TYPEDADDRESS` : Typed address operator (@)

In the `{$T+}` or `{$TYPEDADDRESS ON}` state the @ operator, when applied to a variable, returns a result of type `^T`, if the type of the variable is `T`. In the `{$T-}` state, the result is always an untyped pointer, which is assignment compatible with all other pointer types.

## 45 `$UNDEF` : Undefine a symbol

The directive

    {$UNDEF name}

un-defines the symbol `name` if it was previously defined. `Name` is case insensitive.

## 46 `$V` or `$VARSTRINGCHECKS` : Var-string checking

When in the `+` or `ON` state, the compiler checks that strings passed as parameters are of the same, identical, string type as the declared parameters of the procedure.

## 47 `$WAIT` : Wait for enter key press

If the compiler encounters a

    {$WAIT}

directive, it will resume compiling only after the user has pressed the enter key. If the generation of info messages is turned on, then the compiler will display the following message:

    Press <return> to continue

before waiting for a keypress.

Remark: This may interfere with automatic compilation processes. It should be used for debugging purposes only.

## 48 `$WARNING` : Generate warning message

If the generation of warnings is turned on, through the `-vw` command-line option or the `{$WARNINGS ON}` directive, then

    {$WARNING This is dubious code}

will display a warning message when the compiler encounters it.

## 49 `$WARNINGS` : Emit warnings

`{$WARNINGS ON}` switches the generation of warnings on. `{$WARNINGS OFF}` switches the generation of warnings off. Contrary to the command-line option `-vw` this is a local switch, this is useful for checking parts of your code.

By default, no warnings are emitted.

## 50 `$X` or `$EXTENDEDSYNTAX` : Extended syntax

Extended syntax allows you to drop the result of a function. This means that you can use a function call as if it were a procedure. Standard this feature is on. You can switch it off using the `{$X-}` or `{$EXTENDEDSYNTAX OFF}`directive.

The following, for instance, will not compile:

    function Func (var Arg : sometype) : longint;
    begin
    ...          { declaration of Func }
    end;

    ...

    {$X-}
    Func (A);

The reason this construct is supported is that you may wish to call a function for certain side-effects it has, but you don't need the function result. In this case you don't need to assign the function result, saving you an extra variable.

The command-line compiler switch `-Sa1` has the same effect as the `{$X+}` directive.

By default, extended syntax is assumed.

#
2 Global directives

Global directives affect the whole of the compilation process. That is why they also have a command-line counterpart. The command-line counterpart is given for each of the directives.

## 1 `$APPTYPE` : Specify type of application (Win32 and AmigaOS only)

The `{$APPTYPE XXX}` accepts one argument that can have two possible values: `GUI` or `CONSOLE`. It is used to tell the WINDOWS Operating system if an application is a console application or a graphical application. By default, a program compiled by Free Pascal is a console application. Running it will display a console window. Specifying the `{$APPTYPE GUI}` directive will mark the application as a graphical application; no console window will be opened when the application is run. If run from the command-line, the command prompt will be returned immediatly after the application was started.

Care should be taken when compiling `GUI` applications; the `Input` and `Output` files are not available in a GUI application, and attempting to read from or write to them will result in a run-time error.

It is possible to determine the application type of a WINDOWS or AMIGA application at runtime. The `IsConsole` constant, declared in the Win32 and Amiga system units as

    Const
      IsConsole : Boolean

contains `True` if the application is a console application, `False` if the application is a GUI application.

## 2 `$D` or `$DEBUGINFO` : Debugging symbols

When this switch is on, the compiler inserts GNU debugging information in the executable. The effect of this switch is the same as the command-line switch `-g`.

By default, insertion of debugging information is off.

## 3 `$DESCRIPTION` : Application description

This switch is recognised for compatibility only, but is ignored completely by the compiler. At a later stage, this switch may be activated.

## 4 `$E` : Emulation of coprocessor

This directive controls the emulation of the coprocessor. There is no command-line counterpart for this directive.

### 1 Intel 80x86 version

When this switch is enabled, all floating point instructions which are not supported by standard coprocessor emulators will give out a warning.

The compiler itself doesn't do the emulation of the coprocessor.

To use coprocessor emulation under DOS go32v2 you must use the emu387 unit, which contains correct initialization code for the emulator.

Under LINUX and most UNIX'es, the kernel takes care of the coprocessor support.

### 2 Motorola 680x0 version

When the switch is on, no floating point opcodes are emitted by the code generator. Instead, internal run-time library routines are called to do the necessary calculations. In this case all real types are mapped to the single IEEE floating point type.

Remark: By default, emulation is on. It is possible to intermix emulation code with real floating point opcodes, as long as the only type used is single or real.

Under LINUX and most UNIX'es, the kernel takes care of the coprocessor support.

## 5 `$G` : Generate 80286 code

This option is recognised for Turbo Pascal compatibility, but is ignored, since the compiler works only on 32-bit and 64-bit processors.

## 6 `$INCLUDEPATH` : Specify include path.

This option serves to specify the include path, where the compiler looks for include files. `{$INCLUDEPATH XXX}` will add `XXX` to the include path. `XXX` can contain one or more paths, separated by semi-colons or colons.

For example:

    {$INCLUDEPATH ../inc;../i386}

    {$I strings.inc}

will add the directories ../inc and ../i386 to the include path of the compiler. The compiler will look for the file strings.inc in both these directories, and will include the first found file. This directive is equivalent to the `-Fi` command-line switch.

Caution is in order when using this directive: If you distribute files, the places of the files may not be the same as on your machine; moreover, the directory structure may be different. In general it would be fair to say that you should avoid using absolute paths, instead use relative paths, as in the example above. Only use this directive if you are certain of the places where the files reside. If you are not sure, it is better practice to use makefiles and makefile variables.

## 7 `$L` or `$LOCALSYMBOLS` : Local symbol information

This switch (not to be confused with the `{$L file}` file linking directive) is recognised for Turbo Pascal compatibility, but is ignored. Generation of symbol information is controlled by the `$D` switch.

## 8 `$LIBRARYPATH` : Specify library path.

This option serves to specify the library path, where the linker looks for static or dynamic libraries. `{$LIBRARYPATH XXX}` will add `XXX` to the library path. `XXX` can contain one or more paths, separated by semi-colons or colons.

For example:

    {$LIBRARYPATH /usr/X11/lib;/usr/local/lib}

    {$LINKLIB X11}

will add the directories /usr/X11/lib and /usr/local/lib to the linker library path. The linker will look for the library libX11.so in both these directories, and use the first found file. This directive is equivalent to the `-Fl` command-line switch.

Caution is in order when using this directive: If you distribute files, the places of the libraries may not be the same as on your machine; moreover, the directory structure may be different. In general it would be fair to say that you should avoid using this directive. If you are not sure, it is better practice to use makefiles and makefile variables.

## 9 `$M` or `$MEMORY` : Memory sizes

This switch can be used to set the heap and stacksize. It's format is as follows:

    {$M StackSize,HeapSize}

where `StackSize` and `HeapSize` should be two integer values, greater than 1024. The first number sets the size of the stack, and the second the size of the heap. (Stack setting is ignored under LINUX, and FREEBSD). The two numbers can be set on the command line using the `-Ch` and `-Cs` switches.

## 10 `$MODE` : Set compiler compatibility mode

The `{$MODE}` sets the compatibility mode of the compiler. This is equivalent to setting one of the command-line options `-So`, `-Sd`, `-Sp` or `-S2`. it has the following arguments:

Default
  Default mode. This reverts back to the mode that was set on the command-line.
Delphi
  Delphi compatibility mode. All object-pascal extensions are enabled. This is the same as the command-line option `-Sd`.
TP
  Turbo pascal compatibility mode. Object pascal extensions are disabled, except ansistrings, which remain valid. This is the same as the command-line option `-So`.
FPC
  FPC mode. This is the default, if no command-line switch is supplied.
OBJFPC
  Object pascal mode. This is the same as the `-S2` command-line option.
GPC
  GNU pascal mode. This is the same as the `-Sp` command-line option.

For an exact description of each of these modes, see appendix , on page .

## 11 `$N` : Numeric processing

This switch is recognised for Turbo Pascal compatibility, but is otherwise ignored, since the compiler always uses the coprocessor for floating point mathematics.

## 12 `$O` : Overlay code generation

This switch is recognised for Turbo Pascal compatibility, but is otherwise ignored.

## 13 `$OBJECTPATH` : Specify object path.

This option serves to specify the object path, where the compiler looks for object files. `{$OBJECTPATH XXX}` will add `XXX` to the object path. `XXX` can contain one or more paths, separated by semi-colons or colons.

For example:

    {$OBJECTPATH ../inc;../i386}

    {$L strings.o}

will add the directories ../inc and ../i386 to the object path of the compiler. The compiler will look for the file strings.o in both these directories, and will link the first found file in the program. This directive is equivalent to the `-Fo` command-line switch.

Caution is in order when using this directive: If you distribute files, the places of the files may not be the same as on your machine; moreover, the directory structure may be different. In general it would be fair to say that you should avoid using absolute paths, instead use relative paths, as in the example above. Only use this directive if you are certain of the places where the files reside. If you are not sure, it is better practice to use makefiles and makefile variables.

## 14 `$S` : Stack checking

The `{$S+}` directive tells the compiler to generate stack checking code. This generates code to check if a stack overflow occurred, i.e. to see whether the stack has grown beyond its maximally allowed size. If the stack grows beyond the maximum size, then a run-time error is generated, and the program will exit with exit code 202.

Specifying `{$S-}` will turn generation of stack-checking code off.

The command-line compiler switch `-Ct` has the same effect as the `{$S+}` directive.

By default, no stack checking is performed.

## 15 `$UNITPATH` : Specify unit path.

This option serves to specify the unit path, where the compiler looks for unit files. `{$UNITPATH XXX}` will add `XXX` to the unit path. `XXX` can contain one or more paths, separated by semi-colons or colons.

For example:

    {$UNITPATH ../units;../i386/units}

    Uses strings;

will add the directories ../units and ../i386/units to the unit path of the compiler. The compiler will look for the file strings.ppu in both these directories, and will link the first found file in the program. This directive is equivalent to the `-Fu` command-line switch.

Caution is in order when using this directive: If you distribute files, the places of the files may not be the same as on your machine; moreover, the directory structure may be different. In general it would be fair to say that you should avoid using absolute paths, instead use relative paths, as in the example above. Only use this directive if you are certain of the places where the files reside. If you are not sure, it is better practice to use makefiles and makefile variables.

## 16 `$W` or `$STACKFRAMES` : Generate stackframes

The `{$W}` switch directove controls the generation of stackframes. In the on state, the compiler will generate a stackframe for every procedure or function.

In the off state, the compiler will omit the generation of a stackframe if the following conditions are satisfied:

- The procedure has no parameters.
- The procedure has no local variables.
- If the procedure is not an `assembler` procedure, it must not have a `asm ...end;` block.
- it is not a constuctor or desctructor.

If these conditions are satisfied, the stack frame will be omitted.

## 17 `$Y` or `$REFERENCEINFO` : Insert Browser information

This switch controls the generation of browser inforation. It is recognized for compatibility with Turbo Pascal and Delphi only, as Browser information generation is not yet fully supported.