$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

From the Free Pascal wiki, page "$warn", as it stood on 2022-09-07 after a change by Kai Burghardt, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.