$warn

{$warn} is a local compiler directive controlling emission of certain messages during compile-time. Messages do not necessarily have to be warnings, but can be messages of any kind. The directive may also promote specific messages to errors.

The (local) compiler directives {$warnings on} and {$warnings off} may turn on or off emission of all warnings all together.

usage

{$warn} requires a message label and a treatment option as arguments, like this:

{$warn 3250 off}

The numeric message label can be retrieved during compilation with the -vq option supplied on the command-line (verbosity: show message numbers). Some messages and groups of messages have an alias, too, which can be seen in the table below.

Beside {$warn 3019 on} or {$warn 3019 off} and the shorthand notation {$warn 3019 +} and {$warn 3019 -} respectively, {$warn} may be used to promote messages to errors. {$warn symbol_experimental error} will make all, if any, hints concerning experimental symbols become (non-fatal) errors. Depending on the selected error treatment, the compiler may stop compiling or continue, unless a threshold of errors has been reached.

Note, demoting messages to errors is not possible. A {$fatal} error will always be fatal.

message labels

FPC messages (excerpt)

index	alias	situations triggering the message
02024		there is a custom defined {$warning}
02077		the directive {$minStackSize} is used, but not supported on the current OS
02078		the directive {$maxStackSize} is used, but not supported on the current OS
03018		a constructor is not defined at public visibility level
03019		a destructor is not defined at public visibility level
03177		a record initialization does not define values for all fields
03211	implicit_variants	the variants unit is required, but has not yet been loaded
03250		a virtual method is overridden with lower visibility
04044		a comparison might be always false (disjunct ranges)
04045		a comparison might be always true (disjunct ranges)
04046	constructing_abstract	constructing an instance of a class with abstract methods
04056		a pointer to ordinal conversion is not portable
04090	zero_nil_compat	converting 0 to nil (integer to pointer)
04104	implicit_string_cast	implicit string type conversion
04105	implicit_string_cast_loss	implicit string type conversion with potential data loss
04106	explicit_string_cast	explicit string type conversion
04107	explicit_string_cast_loss	explicit string type conversion with potential data loss
04108	cvt_narrowing_string_lost	Unicode constant cast with potential data loss
04116	intf_raise_visibility	the interface defines a broader visibility for a method
04122	constructing_abstract	constructing an instance of an abstract class
05023		a unit is imported, but not used (except units containing initialization/finalization code)
05024		a routine parameter remains unused
05033	no_retval	no (for the compiler obvious) assignment to a function’s return value
05036		a variable which might not yet have been initialized is used
05043	symbol_deprecated	a symbol with the deprecated hint (no deprecation message defined) is used
05044	symbol_platform	a symbol with the platform hint is used
05055	symbol_unimplemented	a symbol with the unimplemented hint is used
05059		inside a function definition its result variable’s value is used, before it has been initialized
05063	symbol_experimental	a symbol with the experimental hint is used
05065	symbol_library	a library symbol is used
05066	symbol_deprecated	a symbol with the deprecated hint is used and a custom deprecation notice has been defined
05073		a private property remains unused
05074	unit_deprecated	a unit with the deprecated hint (without a custom deprecation message supplied) is used
05075	unit_deprecated	a unit with the deprecated hint is used and a custom deprecation notice has been defined
05076	unit_platform	a unit with the platform hint is used
05077	unit_library	[to be explained]
05078	unit_unimplemented	a unit with the unimplemented hint is used
05079	unit_experimental	a unit with the experimental hint is used
06018		the compiler has determined there is, or might be, unreachable code
07104		register indirect addressing with ebp is used in conjunction with a negative offset

Note, some aliases identify multiple messages.

see also

• § “$WARN: Control emission of warnings” in the Free Pascal programmer’s guide
• {$message}
• Turn warnings and hints on or off