1================================ 2Frequently Asked Questions (FAQ) 3================================ 4 5.. contents:: 6 :local: 7 8Driver 9====== 10 11I run ``clang -cc1 ...`` and get weird errors about missing headers 12------------------------------------------------------------------- 13 14Given 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 25If 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 37for your system. To see these options, run: 38 39.. code-block:: console 40 41 $ clang -### -c hello.c 42 43Some clang command line options are driver-only options, some are frontend-only 44options. Frontend-only options are intended to be used only by clang developers. 45Users should not run ``clang -cc1`` directly, because ``-cc1`` options are not 46guaranteed to be stable. 47 48If 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 50driver 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 54I get errors about some headers being missing (``stddef.h``, ``stdarg.h``) 55-------------------------------------------------------------------------- 56 57Some header files (``stddef.h``, ``stdarg.h``, and others) are shipped with 58Clang --- these are called builtin includes. Clang searches for them in a 59directory relative to the location of the ``clang`` binary. If you moved the 60``clang`` binary, you need to move the builtin headers, too. 61 62More information can be found in the :ref:`libtooling_builtin_includes` 63section. 64 65