Provided by: gdc-13_13.2.0-4ubuntu3_amd64 
NAME
gdc - A GCC-based compiler for the D language
SYNOPSIS
gdc [-c|-S] [-g] [-pg]
[-Olevel] [-Wwarn...]
[-Idir...] [-Ldir...]
[-foption...] [-mmachine-option...]
[-o outfile] [@file] infile...
Only the most useful options are listed here; see below for the remainder.
DESCRIPTION
The gdc command is the GNU compiler for the D language and supports many of the same
options as gcc. This manual only documents the options specific to gdc.
OPTIONS
Input and Output files
For any given input file, the file name suffix determines what kind of compilation is
done. The following kinds of input file names are supported:
file.d
D source files.
file.dd
Ddoc source files.
file.di
D interface files.
You can specify more than one input file on the gdc command line, each being compiled
separately in the compilation process. If you specify a "-o file" option, all the input
files are compiled together, producing a single output file, named file. This is allowed
even when using "-S" or "-c".
A D interface file contains only what an import of the module needs, rather than the whole
implementation of that module. They can be created by gdc from a D source file by using
the "-H" option. When the compiler resolves an import declaration, it searches for
matching .di files first, then for .d.
A Ddoc source file contains code in the D macro processor language. It is primarily
designed for use in producing user documentation from embedded comments, with a slight
affinity towards HTML generation. If a .d source file starts with the string "Ddoc" then
it is treated as general purpose documentation, not as a D source file.
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=value
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
-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:
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.
bitfields
Implements bit-fields in D.
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.
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.
dip1000
Reverts <https://github.com/dlang/DIPs/blob/master/DIPs/other/DIP1000.md> (Scoped
pointers).
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.
intpromote
Turns off C-style integral promotion for unary "+", "-" and "~" expressions.
-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:
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.
Options for Directory Search
These options specify directories to search for files, libraries, and other parts of the
compiler:
-Idir
Specify a directory to use when searching for imported modules at compile time.
Multiple -I options can be used, and the paths are searched in the same order.
-Jdir
Specify a directory to use when searching for files in string imports at compile time.
This switch is required in order to use "import(file)" expressions. Multiple -J
options can be used, and the paths are searched in the same order.
-Ldir
When linking, specify a library search directory, as with gcc.
-Bdir
This option specifies where to find the executables, libraries, source files, and data
files of the compiler itself, as with gcc.
-fmodule-file=module=spec
This option manipulates file paths of imported modules, such that if an imported
module matches all or the leftmost part of module, the file path in spec is used as
the location to search for D sources. This is used when the source file path and
names are not the same as the package and module hierarchy. Consider the following
examples:
gdc test.d -fmodule-file=A.B=foo.d -fmodule-file=C=bar
This will tell the compiler to search in all import paths for the source file foo.d
when importing A.B, and the directory bar/ when importing C, as annotated in the
following D code:
module test;
import A.B; // Matches A.B, searches for foo.d
import C.D.E; // Matches C, searches for bar/D/E.d
import A.B.C; // No match, searches for A/B/C.d
-imultilib dir
Use dir as a subdirectory of the gcc directory containing target-specific D sources
and interfaces.
-iprefix prefix
Specify prefix as the prefix for the gcc directory containing target-specific D
sources and interfaces. If the prefix represents a directory, you should include the
final '/'.
-nostdinc
Do not search the standard system directories for D source and interface files. Only
the directories that have been specified with -I options (and the directory of the
current file, if appropriate) are searched.
Code Generation
In addition to the many gcc options controlling code generation, gdc has several options
specific to itself.
-H Generates D interface files for all modules being compiled. The compiler determines
the output file based on the name of the input file, removes any directory components
and suffix, and applies the .di suffix.
-Hd dir
Same as -H, but writes interface files to directory dir. This option can be used with
-Hf file to independently set the output file and directory path.
-Hf file
Same as -H but writes interface files to file. This option can be used with -Hd dir
to independently set the output file and directory path.
-M Output the module dependencies of all source files being compiled in a format suitable
for make. The compiler outputs one make rule containing the object file name for that
source file, a colon, and the names of all imported files.
-MM Like -M but does not mention imported modules from the D standard library package
directories.
-MF file
When used with -M or -MM, specifies a file to write the dependencies to. When used
with the driver options -MD or -MMD, -MF overrides the default dependency output file.
-MG This option is for compatibility with gcc, and is ignored by the compiler.
-MP Outputs a phony target for each dependency other than the modules being compiled,
causing each to depend on nothing.
-MT target
Change the target of the rule emitted by dependency generation to be exactly the
string you specify. If you want multiple targets, you can specify them as a single
argument to -MT, or use multiple -MT options.
-MQ target
Same as -MT, but it quotes any characters which are special to make.
-MD This option is equivalent to -M -MF file. The driver determines file by removing any
directory components and suffix from the input file, and then adding a .deps suffix.
-MMD
Like -MD but does not mention imported modules from the D standard library package
directories.
-X Output information describing the contents of all source files being compiled in JSON
format to a file. The driver determines file by removing any directory components and
suffix from the input file, and then adding a .json suffix.
-Xf file
Same as -X, but writes all JSON contents to the specified file.
-fdoc
Generates "Ddoc" documentation and writes it to a file. The compiler determines file
by removing any directory components and suffix from the input file, and then adding a
.html suffix.
-fdoc-dir=dir
Same as -fdoc, but writes documentation to directory dir. This option can be used
with -fdoc-file=file to independently set the output file and directory path.
-fdoc-file=file
Same as -fdoc, but writes documentation to file. This option can be used with
-fdoc-dir=dir to independently set the output file and directory path.
-fdoc-inc=file
Specify file as a Ddoc macro file to be read. Multiple -fdoc-inc options can be used,
and files are read and processed in the same order.
-fdump-c++-spec=file
For D source files, generate corresponding C++ declarations in file.
-fdump-c++-spec-verbose
In conjunction with -fdump-c++-spec= above, add comments for ignored declarations in
the generated C++ header.
-fsave-mixins=file
Generates code expanded from D "mixin" statements and writes the processed sources to
file. This is useful to debug errors in compilation and provides source for debuggers
to show when requested.
Warnings
Warnings are diagnostic messages that report constructions that are not inherently
erroneous but that are risky or suggest there is likely to be a bug in the program.
Unless -Werror is specified, they do not prevent compilation of the program.
-Wall
Turns on all warnings messages. Warnings are not a defined part of the D language,
and all constructs for which this may generate a warning message are valid code.
-Walloca
This option warns on all uses of "alloca" in the source.
-Walloca-larger-than=n
Warn on unbounded uses of alloca, and on bounded uses of alloca whose bound can be
larger than n bytes. -Wno-alloca-larger-than disables -Walloca-larger-than warning
and is equivalent to -Walloca-larger-than=SIZE_MAX or larger.
-Wno-builtin-declaration-mismatch
Warn if a built-in function is declared with an incompatible signature.
-Wcast-result
Warn about casts that will produce a null or zero result. Currently this is only done
for casting between an imaginary and non-imaginary data type, or casting between a D
and C++ class.
-Wno-deprecated
Do not warn about usage of deprecated features and symbols with "deprecated"
attributes.
-Werror
Turns all warnings into errors.
-Wextra
This enables some extra warning flags that are not enabled by -Wall.
-Waddress -Wcast-result -Wmismatched-special-enum -Wunknown-pragmas
-Wmismatched-special-enum
Warn when an enum the compiler recognizes as special is declared with a different size
to the built-in type it is representing.
-Wspeculative
List all error messages from speculative compiles, such as "__traits(compiles, ...)".
This option does not report messages as warnings, and these messages therefore never
become errors when the -Werror option is also used.
-Wunknown-pragmas
Warn when a "pragma()" is encountered that is not understood by gdc. This differs
from -fignore-unknown-pragmas where a pragma that is part of the D language, but not
implemented by the compiler, won't get reported.
-Wno-varargs
Do not warn upon questionable usage of the macros used to handle variable arguments
like "va_start".
-fignore-unknown-pragmas
Turns off errors for unsupported pragmas.
-fmax-errors=n
Limits the maximum number of error messages to n, at which point gdc bails out rather
than attempting to continue processing the source code. If n is 0 (the default),
there is no limit on the number of error messages produced.
-fsyntax-only
Check the code for syntax errors, but do not actually compile it. This can be used in
conjunction with -fdoc or -H to generate files for each module present on the command-
line, but no other output file.
-ftransition=id
Report additional information about D language changes identified by id. The
following values are supported:
all List information on all D language transitions.
complex
List all usages of complex or imaginary types.
field
List all non-mutable fields which occupy an object instance.
in List all usages of "in" on parameter.
nogc
List all hidden GC allocations.
templates
List statistics on template instantiations.
tls List all variables going into thread local storage.
Options for Linking
These options come into play when the compiler links object files into an executable
output file. They are meaningless if the compiler is not doing a link step.
-defaultlib=libname
Specify the library to use instead of libphobos when linking. Options specifying the
linkage of libphobos, such as -static-libphobos or -shared-libphobos, are ignored.
-debuglib=libname
Specify the debug library to use instead of libphobos when linking. This option has
no effect unless the -g option was also given on the command line. Options specifying
the linkage of libphobos, such as -static-libphobos or -shared-libphobos, are ignored.
-nophoboslib
Do not use the Phobos or D runtime library when linking. Options specifying the
linkage of libphobos, such as -static-libphobos or -shared-libphobos, are ignored.
The standard system libraries are used normally, unless -nostdlib or -nodefaultlibs is
used.
-shared-libphobos
On systems that provide libgphobos and libgdruntime as a shared and a static library,
this option forces the use of the shared version. If no shared version was built when
the compiler was configured, this option has no effect.
-static-libphobos
On systems that provide libgphobos and libgdruntime as a shared and a static library,
this option forces the use of the static version. If no static version was built when
the compiler was configured, this option has no effect.
Developer Options
This section describes command-line options that are primarily of interest to developers
or language tooling.
-fdump-d-original
Output the internal front-end AST after the "semantic3" stage. This option is only
useful for debugging the GNU D compiler itself.
-v Dump information about the compiler language processing stages as the source program
is being compiled. This includes listing all modules that are processed through the
"parse", "semantic", "semantic2", and "semantic3" stages; all "import" modules and
their file paths; and all "function" bodies that are being compiled.
SEE ALSO
gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entries for gdc and gcc.
COPYRIGHT
Copyright (c) 2006-2023 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of
the GNU Free Documentation License, Version 1.3 or any later version published by the Free
Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the man page gfdl(7).