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Frequently Asked Questions (FAQ)
.. contents::
I run ``clang -cc1 ...`` and get weird errors about missing headers
Given this source file:
.. code-block:: c
#include <stdio.h>
int main() {
printf("Hello world\n");
If you run:
.. code-block:: console
$ clang -cc1 hello.c
hello.c:1:10: fatal error: 'stdio.h' file not found
#include <stdio.h>
1 error generated.
``clang -cc1`` is the frontend, ``clang`` is the :doc:`driver
<DriverInternals>`. The driver invokes the frontend with options appropriate
for your system. To see these options, run:
.. code-block:: console
$ clang -### -c hello.c
Some clang command line options are driver-only options, some are frontend-only
options. Frontend-only options are intended to be used only by clang developers.
Users should not run ``clang -cc1`` directly, because ``-cc1`` options are not
guaranteed to be stable.
If you want to use a frontend-only option ("a ``-cc1`` option"), for example
``-ast-dump``, then you need to take the ``clang -cc1`` line generated by the
driver and add the option you need. Alternatively, you can run
``clang -Xclang <option> ...`` to force the driver pass ``<option>`` to
``clang -cc1``.
I get errors about some headers being missing (``stddef.h``, ``stdarg.h``)
Some header files (``stddef.h``, ``stdarg.h``, and others) are shipped with
Clang --- these are called builtin includes. Clang searches for them in a
directory relative to the location of the ``clang`` binary. If you moved the
``clang`` binary, you need to move the builtin headers, too.
More information can be found in the :ref:`libtooling_builtin_includes`