Command Section
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
       preprocessing, 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
              target 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 <> 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
              optimization 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
              executable 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
              supported by your application.

              When building for iPhone OS, specify the minimum version
              supported 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

                 -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
                 compliance 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
              assumption that the debug type information can be spread out
              over multiple 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
              generated to detect this and abort when it happens.

              This flag sets the default visibility level.

              This flag specifies that variables without initializers get
              common 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
              intermediate language assembly files, otherwise this generates
              LLVM bitcode 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
              integrated 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,
       -fdiagnostics-fixit-info, -fdiagnostics-parseable-fixits,
       -fdiagnostics-print-source-range-info, -fprint-source-range-info,
       -fdiagnostics-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
              location 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

              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 <>.  Most bug reports
       should include preprocessed source files (use the -E option) and the
       full output of the compiler, along with information to reproduce.

       as(1), ld(1)

       Maintained by the Clang / LLVM Team (<>)

       2007-2016, The Clang Team

3.8                              March 4, 2016                        CLANG(1)
Command Section