Linux Command Library


clang - the Clang C and Objective-C compiler

- Compile a source code file into an executable binary:
clang [input_source.c] -o [output_executable]

- Activate output of all errors and warnings:
clang [input_source.c] -Wall -o [output_executable]

- Include libraries located at a different path than the source file:
clang [input_source.c] -o [output_executable] -I[header_path] -L[library_path] -l[library_name]

clang [-c|-S|-E] -std=standard -g [-O0|-O1|-O2|-Os|-O3|-O4] -Wwarnings... -pedantic -Idir... -Ldir... -Dmacro[=defn] -ffeature-option... -mmachine-option... -o output-file input-filenames

clang is a 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 tools.Preprocessing 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) or .mi (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 parser 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-specfic 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.

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.The

Clang Static Analyzer

The Clang Static Analyzer is a tool that scans source code to try to find bugs though code analysis. This tool uses many parts of Clang and is built into the same driver.

Stage Selection Options -E

Run the preprocessor stage.-fsyntax-only 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.


Run all of the above, plus the assembler, generating a target .o object 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.--analyze Run the Clang Static Analyzer.

Language Selection and Mode Options -x Treat subsequent input files as having type language.-std=Specify the language standard to compile for.-ansi Same as -std=c89.-ObjC++ Treat source input files as Objective-C ++ inputs.-ObjC Treat source input files as Objective-C inputs.-trigraphs Enable trigraphs.-ffreestanding Indicate that the file should be compiled for a freestanding, not a hosted, environment.-fno-builtin Disable special handling and optimizations of builtin functions like strlen and malloc.-fmath-errno Indicate that math functions should be treated as updating errno.-fpascal-strings Enable support for Pascal-style strings with pfoo.-fms-extensions Enable support for Microsoft extensions.-fborland-extensions Enable support for Borland extensions.-fwritable-strings Make all string literals default to writable. This disables uniquing of strings and other optimizations.-flax-vector-conversions Allow loose type checking rules for implicit vector conversions.-fblocks Enable the Blocks language feature.-fobjc-gc-only Indicate that Objective-C code should be compiled in GC-only mode, which only works when Objective-C Garbage Collection is enabled.-fobjc-gc Indicate that Objective-C code should be compiled in hybrid-GC mode, which works with both GC and non-GC mode.

Target Selection Options -arch Specify the architecture to build for.-mmacosx-version-min=When building for Mac OS/X , specify the minimum version supported by your application.-miphoneos-version-min When building for iPhone OS , specify the minimum version supported by your application.-march=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 -Os -O3 -O4 Specify which optimization level to use. -O0 means no optimization: this level compiles the fastest and generates the most debuggable code. -O2 is a moderate level of optimization which enables most optimizations. -Os is like -O2 with extra optimizations to reduce code size. -O3 is 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). On supported platforms, -O4 enables link-time optimization; object files are stored in the LLVM bitcode file format and whole program optimization is done at link time. -O1 is somewhere between -O0 and -O2.-g

Generate debug information. Note that Clang debug information works best at -O0. At higher optimization levels, only line number information is currently available.-fexceptions Enable generation of unwind information, this allows exceptions to be thrown through Clang compiled stack frames. This is on by default in x86-64.-ftrapv 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.-fvisibility This flag sets the default visibility level.-fcommon This flag specifies that variables without initializers get common linkage. It can be disabled with -fno-common.-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 the commands to run for this compilation.--help Display available options.-Qunused-arguments Dont emit warning for unused driver arguments.-Wa,argsPass the comma separated arguments in args to the assembler.-Wl,argsPass the comma separated arguments in args to the linker.-Wp,argsPass the comma separated arguments in args to the preprocessor.-Xanalyzer Pass arg to the static analyzer.-Xassembler Pass arg to the assembler.-Xclang Pass arg to the clang compiler frontend.-Xlinker Pass arg to the linker.-mllvm Pass arg to the LLVM backend.-Xpreprocessor Pass arg to the preprocessor.-o Write output to file.-print-file-name=Print the full library path of file.-print-libgcc-file-name Print the library path for libgcc.a.-print-prog-name=Print the full program path of name.-print-search-dirs Print the paths used for finding libraries and programs.-save-temps 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.-ftime-report 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 Users Manual for more information.

Preprocessor Options -Dmacroname=valueAdds an implicit #define into the predefines buffer which is read before the source file is preprocessed.-UmacronameAdds an implicit #undef into the predefines buffer which is read before the source file is preprocessed.-include Adds an implicit #include into the predefines buffer which is read before the source file is preprocessed.-IdirectoryAdd the specified directory to the search path for include files.-FdirectoryAdd the specified directory to the search path for framework include files.-nostdinc Do not search the standard system directories for include files.-nobuiltininc Do not search clangs builtin directory for include files.

TMPDIR , TEMP , TMP These environment variables are checked, in order, for the location to write temporary files used during the compilation process.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 delimitor, as used in the PATH environment variable.

Empty components in the environment variable are ignored.

C_INCLUDE_PATH, OBJC_INCLUDE_PATH , CPLUS_INCLUDE_PATH , OBJCPLUS_INCLUDE_PATH These environment variables specify additional paths, as for CPATH , which are only used when processing the appropriate language.MACOSX_DEPLOYMENT_TARGET 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

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