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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 a frontend to gcc and supports many of the same options.    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, in which case they will
       all be compiled.  If you specify a "-o file" option, all the input files will be 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 array 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 will never throw 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 that do not begin with __builtin_ as prefix.  By
           default, the compiler will recognize when a function in the "core.stdc" package is a
           built-in function.

       -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:

           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-invariants
           Turns off code generation for class "invariant" contracts.

       -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 will not be generated include module constructor 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.

       -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 behaviour.

           This is equivalent to compiling with the following options:

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

       -fno-switch-errors
           This option controls what code should be generated when no case is matched in a "final
           switch" statement.  The default run time behavior is that a "SwitchError" will be
           thrown.  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
           Turns off emission of instantiated declarations that can be defined in multiple
           objects as weak or one-only symbols.  The default is to emit all public symbols as
           weak, unless there lacks target support.  Disabling this options 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 hierachy.  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 dir directory.  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 based on the
           name of the input file, removes any directory components and suffix, and applies 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 based on the name of the input file,
           removes any directory components and suffix, and applies a .json suffix.

       -Xf file
           Same as -X, but writes all JSON contents to the specified file.

       -fdoc
           Generates "Ddoc" documentation and writes to a file.  The compiler determines file
           based on the name of the input file, removes any directory components and suffix, and
           applies a .html suffix.

       -fdoc-dir=dir
           Same as -fdoc, but writes documentation to dir directory.  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.

   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 legal code.

       -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.

       -Wspeculative
           Report on 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.

       -Wtemplates
           Warn when a template instantiation is encountered.  Some coding rules disallow
           templates, and this may be used to enforce that rule.

       -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, will not get reported.

       -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 only
           suppresses the generation of the object code, and can be used in conjunction with
           -fdoc or -H options.

       -ftransition=id
           Report additional information about D language changes identified by id.  The
           following values are supported:

           all List information on all language changes.

           checkimports
               Give deprecation messages about -ftransition=import anomalies.

           complex
               List all usages of complex or imaginary types.

           dip1000
               Implements <http://wiki.dlang.org/DIP1000> (experimental).

           dip25
               Implements <http://wiki.dlang.org/DIP25> (experimental).

           field
               List all non-mutable fields which occupy an object instance.

           import
               Tells the compiler to revert to using an old lookup behavior for resolving
               unqualified symbol names, where this was done in a single pass, ignoring any
               protection attributes.  The default name lookup strategy is to use two passes, the
               first ignoring imported declarations, and the second only looking at imports.  The
               protection ("private", "package", "protected") of symbols is also enforced to
               resolve any conflicts between private and public symbols.

           nogc
               List all hidden GC allocations.

           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
           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
           Dump the front-end AST after after parsing and running semantic on the source program.
           Only really useful for debugging the 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) 2006-2018 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, the Front-Cover Texts being (a) (see
       below), and with the Back-Cover Texts being (b) (see below).  A copy of the license is
       included in the man page gfdl(7).

       (a) The FSF's Front-Cover Text is:

            A GNU Manual

       (b) The FSF's Back-Cover Text is:

            You have freedom to copy and modify this GNU Manual, like GNU
            software.  Copies published by the Free Software Foundation raise
            funds for GNU development.