Runtime Options#

These options affect the runtime behavior of programs compiled with gdc.

-fall-instantiations#: Generate code for all template instantiations. The default template emission strategy is to not generate code for declarations that were either instantiated speculatively, such as from __traits(compiles, ...), or that come from an imported module not being compiled.

-fno-assert#: Turn off code generation for assert contracts.

-fno-bounds-check#: Turns off array bounds checking for all functions, which can improve performance for code that uses arrays extensively. Note that this can result in unpredictable behavior if the code in question actually does violate array bounds constraints. It is safe to use this option if you are sure that your code never throws a RangeError.

-fbounds-check=value#

An alternative to -fbounds-check that allows more control as to where bounds checking is turned on or off. The following values are supported:

on: Turns on array bounds checking for all functions.
safeonly: Turns on array bounds checking only for @safe functions.
off: Turns off array bounds checking completely.

-fno-builtin#: Don’t recognize built-in functions unless they begin with the prefix __builtin_. By default, the compiler will recognize when a function in the core.stdc package is a built-in function.

-fcheckaction#

This option controls what code is generated on an assertion, bounds check, or final switch failure. The following values are supported:

context: Throw an AssertError with extra context information.
halt: Halt the program execution.
throw: Throw an AssertError (the default).

-fdebug=value#

Turn on compilation of conditional debug code into the program. The -fdebug option itself sets the debug level to 1, while -fdebug= enables debug code that are identified by any of the following values:

level: Sets the debug level to level, any debug code <= level is compiled into the program.
ident: Turns on compilation of any debug code identified by ident.

-fno-druntime#

Implements https://dlang.org/spec/betterc.html. Assumes that compilation targets an environment without a D runtime library.

This is equivalent to compiling with the following options:

gdc -nophoboslib -fno-exceptions -fno-moduleinfo -fno-rtti

-fextern-std=standard#

Sets the C++ name mangling compatibility to the version identified by standard. The following values are supported:

c++98, c++03: Sets __traits(getTargetInfo, "cppStd") to 199711.
c++11: Sets __traits(getTargetInfo, "cppStd") to 201103.
c++14: Sets __traits(getTargetInfo, "cppStd") to 201402.
c++17: Sets __traits(getTargetInfo, "cppStd") to 201703. This is the default.
c++20: Sets __traits(getTargetInfo, "cppStd") to 202002.

-fno-invariants#: Turns off code generation for class invariant contracts.

-fmain#: Generates a default main() function when compiling. This is useful when unittesting a library, as it enables running the unittests in a library without having to manually define an entry-point function. This option does nothing when main is already defined in user code.

-fno-moduleinfo#: Turns off generation of the ModuleInfo and related functions that would become unreferenced without it, which may allow linking to programs not written in D. Functions that are not be generated include module constructors and destructors (static this and static ~this), unittest code, and DSO registry functions for dynamically linked code.

-fonly=filename#: Tells the compiler to parse and run semantic analysis on all modules on the command line, but only generate code for the module specified by filename.

-fno-postconditions#: Turns off code generation for postcondition out contracts.

-fno-preconditions#: Turns off code generation for precondition in contracts.

-fpreview=id#

Turns on an upcoming D language change identified by id. The following values are supported:

all: Turns on all upcoming D language features.
dip1000: Implements https://github.com/dlang/DIPs/blob/master/DIPs/other/DIP1000.md (Scoped pointers).
dip1008: Implements https://github.com/dlang/DIPs/blob/master/DIPs/other/DIP1008.md (Allow exceptions in @nogc code).
dip1021: Implements https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1021.md (Mutable function arguments).
dip25: Implements https://github.com/dlang/DIPs/blob/master/DIPs/archive/DIP25.md (Sealed references).
dtorfields: Turns on generation for destructing fields of partially constructed objects.
fieldwise: Turns on generation of struct equality to use field-wise comparisons.
fixaliasthis: Implements new lookup rules that check the current scope for alias this before searching in upper scopes.
fiximmutableconv: Disallows unsound immutable conversions that were formerly incorrectly permitted.
in: Implements in parameters to mean scope const [ref] and accepts rvalues.
inclusiveincontracts: Implements in contracts of overridden methods to be a superset of parent contract.
intpromote: Implements C-style integral promotion for unary +, - and ~ expressions.
nosharedaccess: Turns off and disallows all access to shared memory objects.
rvaluerefparam: Implements rvalue arguments to ref parameters.
systemvariables: Disables access to variables marked @system from @safe code.

-frelease#

Turns on compiling in release mode, which means not emitting runtime checks for contracts and asserts. Array bounds checking is not done for @system and @trusted functions, and assertion failures are undefined behavior.

This is equivalent to compiling with the following options:

gdc -fno-assert -fbounds-check=safe -fno-invariants \
    -fno-postconditions -fno-preconditions -fno-switch-errors

-frevert=#

Turns off a D language feature identified by id. The following values are supported:

all: Turns off all revertable D language features.
dip25: Reverts https://github.com/dlang/DIPs/blob/master/DIPs/archive/DIP25.md (Sealed references).
dtorfields: Turns off generation for destructing fields of partially constructed objects.
markdown: Turns off Markdown replacements in Ddoc comments.

-fno-rtti#: Turns off generation of run-time type information for all user defined types. Any code that uses features of the language that require access to this information will result in an error.

-fno-switch-errors#: This option controls what code is generated when no case is matched in a final switch statement. The default run time behavior is to throw a SwitchError. Turning off -fswitch-errors means that instead the execution of the program is immediately halted.

-funittest#: Turns on compilation of unittest code, and turns on the version(unittest) identifier. This implies -fassert.

-fversion=value#

Turns on compilation of conditional version code into the program identified by any of the following values:

level: Sets the version level to level, any version code >= level is compiled into the program.
ident: Turns on compilation of version code identified by ident.

-fno-weak-templates#: Turns off emission of declarations that can be defined in multiple objects as weak symbols. The default is to emit all public symbols as weak, unless the target lacks support for weak symbols. Disabling this option means that common symbols are instead put in COMDAT or become private.