Frequently Asked Questions (FAQ) — Clang 21.0.0git documentation (original) (raw)

• Driver
  • I run clang -cc1 ... and get weird errors about missing headers
  • I get errors about some headers being missing (stddef.h, stdarg.h)

Driver¶

I run clang -cc1 ... and get weird errors about missing headers¶

Given this source file:

#include <stdio.h>

int main() { printf("Hello world\n"); }

If you run:

$ 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 driver. The driver invokes the frontend with options appropriate for your system. To see these options, run:

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 runclang -Xclang <option> ... to force the driver pass <option> toclang -cc1.