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