1 ================================ 2 Frequently Asked Questions (FAQ) 3 ================================ 4 5 .. contents:: 6 :local: 7 8 Driver 9 ====== 10 11 I run ``clang -cc1 ...`` and get weird errors about missing headers 12 ------------------------------------------------------------------- 13 14 Given this source file: 15 16 .. code-block:: c 17 18 #include <stdio.h> 19 20 int main() { 21 printf("Hello world\n"); 22 } 23 24 25 If you run: 26 27 .. code-block:: console 28 29 $ clang -cc1 hello.c 30 hello.c:1:10: fatal error: 'stdio.h' file not found 31 #include <stdio.h> 32 ^ 33 1 error generated. 34 35 ``clang -cc1`` is the frontend, ``clang`` is the :doc:`driver 36 <DriverInternals>`. The driver invokes the frontend with options appropriate 37 for your system. To see these options, run: 38 39 .. code-block:: console 40 41 $ clang -### -c hello.c 42 43 Some clang command line options are driver-only options, some are frontend-only 44 options. Frontend-only options are intended to be used only by clang developers. 45 Users should not run ``clang -cc1`` directly, because ``-cc1`` options are not 46 guaranteed to be stable. 47 48 If you want to use a frontend-only option ("a ``-cc1`` option"), for example 49 ``-ast-dump``, then you need to take the ``clang -cc1`` line generated by the 50 driver and add the option you need. Alternatively, you can run 51 ``clang -Xclang <option> ...`` to force the driver pass ``<option>`` to 52 ``clang -cc1``. 53 54 I get errors about some headers being missing (``stddef.h``, ``stdarg.h``) 55 -------------------------------------------------------------------------- 56 57 Some header files (``stddef.h``, ``stdarg.h``, and others) are shipped with 58 Clang --- these are called builtin includes. Clang searches for them in a 59 directory relative to the location of the ``clang`` binary. If you moved the 60 ``clang`` binary, you need to move the builtin headers, too. 61 62 More information can be found in the :ref:`libtooling_builtin_includes` 63 section. 64 65
