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Updated: Thursday, June 13, 2019

clang (1)


clang - C compiler


clang [options] filename ...


CLANG(1)                             Clang                            CLANG(1)

       clang - the Clang C, C++, and Objective-C compiler

       clang [options] filename ...

       clang  is  a C, C++, and Objective-C compiler which encompasses prepro-
       cessing, parsing, optimization, code generation, assembly, and linking.
       Depending  on  which high-level mode setting is passed, Clang will stop
       before doing a full link.  While Clang  is  highly  integrated,  it  is
       important to understand the stages of compilation, to understand how to
       invoke it.  These stages are:

       Driver The clang executable is actually a small driver  which  controls
              the  overall  execution  of  other  tools  such as the compiler,
              assembler and linker.  Typically you do  not  need  to  interact
              with  the  driver, but you transparently use it to run the other

              This stage handles tokenization of the input source file,  macro
              expansion, #include expansion and handling of other preprocessor
              directives.  The output of this stage is typically called a ".i"
              (for  C),  ".ii"  (for  C++), ".mi" (for Objective-C), or ".mii"
              (for Objective-C++) file.

       Parsing and Semantic Analysis
              This stage  parses  the  input  file,  translating  preprocessor
              tokens  into a parse tree.  Once in the form of a parse tree, it
              applies semantic analysis to compute types  for  expressions  as
              well  and  determine whether the code is well formed. This stage
              is responsible for generating most of the compiler  warnings  as
              well  as  parse errors. The output of this stage is an "Abstract
              Syntax Tree" (AST).

       Code Generation and Optimization
              This stage translates an AST into  low-level  intermediate  code
              (known as "LLVM IR") and ultimately to machine code.  This phase
              is responsible for optimizing the generated  code  and  handling
              target-specific  code  generation.   The output of this stage is
              typically called a ".s" file or "assembly" file.

              Clang also supports the use of an integrated assembler, in which
              the  code  generator produces object files directly. This avoids
              the overhead of generating the ".s" file and of calling the tar-
              get assembler.

              This  stage runs the target assembler to translate the output of
              the compiler into a target object file. The output of this stage
              is typically called a ".o" file or "object" file.

       Linker This stage runs the target linker to merge multiple object files
              into an executable or dynamic library. The output of this  stage
              is typically called an "a.out", ".dylib" or ".so" file.

       Clang Static Analyzer

       The  Clang  Static  Analyzer is a tool that scans source code to try to
       find bugs through code analysis.  This tool uses many  parts  of  Clang
       and    is    built    into    the   same   driver.    Please   see   <-
       http://clang-analyzer.llvm.org> for more details  on  how  to  use  the
       static analyzer.

   Stage Selection Options
       -E     Run the preprocessor stage.

              Run the preprocessor, parser and type checking stages.

       -S     Run the previous stages as well as LLVM generation and optimiza-
              tion stages and target-specific code  generation,  producing  an
              assembly file.

       -c     Run  all  of  the above, plus the assembler, generating a target
              ".o" object file.

       no stage selection option
              If no stage selection option is specified, all stages above  are
              run,  and  the linker is run to combine the results into an exe-
              cutable or shared library.

   Language Selection and Mode Options
       -x <language>
              Treat subsequent input files as having type language.

              Specify the language standard to compile for.

              Specify the C++ standard library to use; supported  options  are
              libstdc++ and libc++.

       -ansi  Same as -std=c89.

       -ObjC, -ObjC++
              Treat  source  input  files as Objective-C and Object-C++ inputs

              Enable trigraphs.

              Indicate that the file should be compiled  for  a  freestanding,
              not a hosted, environment.

              Disable  special handling and optimizations of builtin functions
              like strlen() and malloc().

              Indicate that math  functions  should  be  treated  as  updating

              Enable support for Pascal-style strings with "\pfoo".

              Enable support for Microsoft extensions.

              Set _MSC_VER. Defaults to 1300 on Windows. Not set otherwise.

              Enable support for Borland extensions.

              Make  all  string  literals  default to writable.  This disables
              uniquing of strings and other optimizations.

              Allow loose type checking rules for implicit vector conversions.

              Enable the "Blocks" language feature.

              Indicate that Objective-C code should  be  compiled  in  GC-only
              mode,  which  only  works when Objective-C Garbage Collection is

              Indicate that Objective-C code should be compiled  in  hybrid-GC
              mode, which works with both GC and non-GC mode.

              Select  the  Objective-C  ABI version to use. Available versions
              are 1 (legacy "fragile" ABI),  2  (non-fragile  ABI  1),  and  3
              (non-fragile ABI 2).

              Select  the  Objective-C  non-fragile  ABI  version  to  use  by
              default. This will only be used as the Objective-C ABI when  the
              non-fragile ABI is enabled (either via -fobjc-nonfragile-abi, or
              because it is the platform default).

              Enable use of the Objective-C non-fragile ABI. On platforms  for
              which  this  is  the  default  ABI,  it  can  be  disabled  with

   Target Selection Options
       Clang fully supports cross compilation  as  an  inherent  part  of  its
       design.   Depending  on how your version of Clang is configured, it may
       have support for a number of cross compilers, or  may  only  support  a
       native target.

       -arch <architecture>
              Specify the architecture to build for.

              When  building  for  Mac  OS X, specify the minimum version sup-
              ported by your application.

              When building for iPhone OS, specify the  minimum  version  sup-
              ported by your application.

              Specify that Clang should generate code for a specific processor
              family  member  and  later.   For  example,   if   you   specify
              -march=i486,  the  compiler  is allowed to generate instructions
              that are valid on i486 and later processors, but which  may  not
              exist on earlier ones.

   Code Generation Options
       -O0, -O1, -O2, -O3, -Ofast, -Os, -Oz, -O, -O4
              Specify which optimization level to use:
                 -O0  Means "no optimization": this level compiles the fastest
                 and generates the most debuggable code.

                 -O1 Somewhere between -O0 and -O2.

                 -O2 Moderate level of optimization which enables  most  opti-

                 -O3  Like -O2, except that it enables optimizations that take
                 longer to perform or that may generate  larger  code  (in  an
                 attempt to make the program run faster).

                 -Ofast  Enables  all  the  optimizations  from -O3 along with
                 other aggressive optimizations that may violate  strict  com-
                 pliance with language standards.

                 -Os Like -O2 with extra optimizations to reduce code size.

                 -Oz Like -Os (and thus -O2), but reduces code size further.

                 -O Equivalent to -O2.

                 -O4 and higher
                     Currently equivalent to -O3

       -g     Generate  debug  information.  Note that Clang debug information
              works best at -O0.

              Generate debug information that contains external references  to
              types defined in clang modules or precompiled headers instead of
              emitting redundant debug  type  information  into  every  object
              file.  This option implies -fmodule-format=obj.

              This  option  should  not be used when building static libraries
              for distribution to other machines because the debug  info  will
              contain references to the module cache on the machine the object
              files in the library were built on.

       -fstandalone-debug -fno-standalone-debug
              Clang supports a number of optimizations to reduce the  size  of
              debug  information in the binary. They work based on the assump-
              tion that the debug type information can be spread out over mul-
              tiple compilation units.  For instance, Clang will not emit type
              definitions for types that are not needed by a module and  could
              be  replaced  with  a  forward declaration.  Further, Clang will
              only emit type info for a dynamic C++ class in the  module  that
              contains the vtable for the class.

              The  -fstandalone-debug  option  turns  off these optimizations.
              This is useful when working with 3rd-party libraries that  don't
              come  with  debug  information.   This is the default on Darwin.
              Note that Clang will never emit type information for types  that
              are not referenced at all by the program.

              Enable  generation of unwind information. This allows exceptions
              to be thrown through Clang compiled stack frames.  This is on by
              default in x86-64.

              Generate  code to catch integer overflow errors.  Signed integer
              overflow is undefined in C. With this flag, extra code is gener-
              ated to detect this and abort when it happens.

              This flag sets the default visibility level.

              This flag specifies that variables without initializers get com-
              mon linkage.  It can be disabled with -fno-common.

              Set the default thread-local storage  (TLS)  model  to  use  for
              thread-local  variables.  Valid  values  are:  "global-dynamic",
              "local-dynamic", "initial-exec" and "local-exec". The default is
              "global-dynamic".  The  default model can be overridden with the
              tls_model attribute. The compiler will  try  to  choose  a  more
              efficient model if possible.

       -flto, -emit-llvm
              Generate  output  files  in LLVM formats, suitable for link time
              optimization.  When used with -S this generates LLVM  intermedi-
              ate  language assembly files, otherwise this generates LLVM bit-
              code format object files (which may  be  passed  to  the  linker
              depending on the stage selection options).

   Driver Options
       -###   Print (but do not run) the commands to run for this compilation.

       --help Display available options.

              Do not emit any warnings for unused driver arguments.

              Pass the comma separated arguments in args to the assembler.

              Pass the comma separated arguments in args to the linker.

              Pass the comma separated arguments in args to the preprocessor.

       -Xanalyzer <arg>
              Pass arg to the static analyzer.

       -Xassembler <arg>
              Pass arg to the assembler.

       -Xlinker <arg>
              Pass arg to the linker.

       -Xpreprocessor <arg>
              Pass arg to the preprocessor.

       -o <file>
              Write output to file.

              Print the full library path of file.

              Print the library path for "libgcc.a".

              Print the full program path of name.

              Print the paths used for finding libraries and programs.

              Save intermediate compilation results.

       -integrated-as, -no-integrated-as
              Used  to  enable and disable, respectively, the use of the inte-
              grated assembler. Whether the  integrated  assembler  is  on  by
              default is target dependent.

       -time  Time individual commands.

              Print timing summary of each stage of compilation.

       -v     Show commands to run and use verbose output.

   Diagnostics Options
       -fshow-column,  -fshow-source-location, -fcaret-diagnostics, -fdiagnos-
       tics-fixit-info,       -fdiagnostics-parseable-fixits,       -fdiagnos-
       tics-print-source-range-info,   -fprint-source-range-info,   -fdiagnos-
       tics-show-option, -fmessage-length
              These options control how Clang  prints  out  information  about
              diagnostics  (errors  and warnings). Please see the Clang User's
              Manual for more information.

   Preprocessor Options
              Adds an implicit #define into the  predefines  buffer  which  is
              read before the source file is preprocessed.

              Adds an implicit #undef into the predefines buffer which is read
              before the source file is preprocessed.

       -include <filename>
              Adds an implicit #include into the predefines  buffer  which  is
              read before the source file is preprocessed.

              Add  the  specified  directory  to  the  search path for include

              Add the specified directory to the  search  path  for  framework
              include files.

              Do  not  search  the  standard  system  directories  or compiler
              builtin directories for include files.

              Do not search the standard system directories for include files,
              but do search compiler builtin include directories.

              Do not search clang's builtin directory for include files.

              These environment variables are checked, in order, for the loca-
              tion to  write  temporary  files  used  during  the  compilation

       CPATH  If  this  environment  variable  is  present, it is treated as a
              delimited list of paths  to  be  added  to  the  default  system
              include  path  list.  The  delimiter  is  the platform dependent
              delimiter, as used in the PATH environment variable.

              Empty components in the environment variable are ignored.

              These  environment  variables  specify  additional paths, as for
              CPATH, which are only used when processing the appropriate  lan-

              If  -mmacosx-version-min  is unspecified, the default deployment
              target is read from this environment variable. This option  only
              affects Darwin targets.

       To report bugs, please visit <http://llvm.org/bugs/>.  Most bug reports
       should include preprocessed source files (use the -E  option)  and  the
       full output of the compiler, along with information to reproduce.

       See attributes(7) for descriptions of the following attributes:

       |Availability   | developer/llvm/clang |
       |Stability      | Uncommitted          |
       as(1), ld(1)

       Maintained by the Clang / LLVM Team (<http://clang.llvm.org>)

       2007-2016, The Clang Team

       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source                was                downloaded                from

       Further information about this software can be found on the open source
       community website at https://llvm.org/.

3.8                              Jul 10, 2016                         CLANG(1)