5.1.5 Options concerning the sources (language options)

For more information on these options, see Programmer’s Guide

Set language mode to mode, which can be one of the following:
Try to be Delphi compatible. This is more strict than the objfpc mode, since some Free Pascal extensions are switched off.
Free Pascal dialect (default).
Try to be compatible with Macintosh Pascal dialects.
Switch on some Delphi extensions. This is different from Delphi mode, because some Free Pascal constructs are still available.
Try to be TP/BP 7.0 compatible. This means no function overloading etc.
Select language feature feature. As of FPC version 2.3.1, the -M command line switch can be used to select individual language features. In that case, feature is one of the following keywords:
Use object pascal classes.
Automatically include the ObjPas unit.
Enable the Result identifier for function results.
Allow automatic conversion of null-terminated strings to strings,
Allow the use of the CVAR keyword.
Allow use of nested comments.
Use classical procedural variables.
Use mac-style procedural variables.
Implementation and Forward declaration must match completely.
Allow silent conversion of pointers to procedural variables.
Automatic (silent) dereferencing of typed pointers.
Allow use of Initialization and Finalization
Allow use of pointer arithmetic.
Allow use of ansistrings.
Allow use of the out parameter type.
Allow use of default parameter values.
Support the hint directives (deprecated, platform etc.)
Allow use of global properties.
Allow inline procedures.
Allow the use of exceptions.

The keyword can be followed by a plus or minus sign to enable or disable the feature.

Specify what kind of assembler you use in your asm assembler code blocks. Here xxx is one of the following:
asm blocks contain AT&T-style assembler. This is the default style.
asm blocks contain Intel-style assembler.
Use the default assembler for the specified target.
asm blocks should be copied as is in the assembler, only replacing certain variables.
Switch on Delphi 2 extensions (objfpc mode). Deprecated, use -Mobjfpc instead.
Include assert statements in compiled code. Omitting this option will cause assert statements to be ignored.
Support C-style operators, i.e. *=, +=, /= and -=.
Try to be Delphi compatible. Deprecated, use -Mdelphi instead.
The compiler stops after the N-th error. Normally, the compiler tries to continue compiling after an error, until 50 errors are reached, or a fatal error is reached, and then it stops. With this switch, the compiler will stop after the N-th error (if N is omitted, a default of 1 is assumed). Instead of a number, one of n, h or w can also be specified. In that case the compiler will consider notes, hints or warnings as errors and stop when one is encountered.
Support the label and goto commands. By default these are not supported. You must also specify this option if you use labels in assembler statements. (if you use the AT&T style assember)
Use ansistrings by default for strings. If this option is specified, the compiler will interpret the string keyword as an ansistring. Otherwise it is supposed to be a shortstring (TP style).
Support C++ style INLINE.
Set interfaces style to XXX.
Load the Kylix compatibility unit (fpcylix).
Support C-style macros.
Try to be Borland TP 7.0 compatible. Deprecated, use -Mtp instead.
The name of constructors must be init, and the name of destructors should be done.
Allow the static keyword in objects.
Enable exception keywords (default in Delphi/Objfpc mode). This will mark all exception related keywords as keywords, also in Turbo Pascal or FPC mode. This can be used to check for code which should be mode-neutral as much as possible.
Do not check the unit name. Normally, the unit name is the same as the filename. This option allows them to be different.
Compile a system unit. This option causes the compiler to define only some very basic types.