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