Re: Word For Today: “Uglification”

On 13/03/2024 16:15, Keith Thompson wrote:

Michael S <already5chosen@yahoo.com> writes:
[...]

I just tried three compilers and [in absence of -I options] all 3 work
as expected, i.e. ignored stdio.h in current directory.
None of the three was of the variety that you appear to prefer.
Mine's are mundane stuff.
>
However all three took local file when I had given them an option -I.
Not sure what to make of this. Whatever happens with
non-default options is probably in "implementation-defined"
domain as far as the C Standard is concerned, but I still
expected that such common option as  -I would not affect standard
headers.

 According to the GNU cpp manual, the "-I" option prepends directories to
the search path used for <> headers, and the "-iquote" option prepends
directories to the search path used for "" headers.
 I find that a bit surprising.

You are not quite correct - and I find /that/ a bit surprising!
The -I option applies equally to <...> and "..." headers.

 I had never heard of the "-iquote"
option.
 

The complete description is here: <https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html>.  (It is the same in the cpp manual, but it is better to look at the compiler manual for this kind of thing - after all, the gcc driver program can pass different options to the cpp subprogram.)
To save people looking it up:
-I dir
-iquote dir
-isystem dir
-idirafter dir
     Add the directory dir to the list of directories to be searched for header files during preprocessing. If dir begins with ‘=’ or $SYSROOT, then the ‘=’ or $SYSROOT is replaced by the sysroot prefix; see --sysroot and -isysroot.
     Directories specified with -iquote apply only to the quote form of the directive, #include "file". Directories specified with -I, -isystem, or -idirafter apply to lookup for both the #include "file" and #include <file> directives.
     You can specify any number or combination of these options on the command line to search for header files in several directories. The lookup order is as follows:
         For the quote form of the include directive, the directory of the current file is searched first.
         For the quote form of the include directive, the directories specified by -iquote options are searched in left-to-right order, as they appear on the command line.
         Directories specified with -I options are scanned in left-to-right order.
         Directories specified with -isystem options are scanned in left-to-right order.
         Standard system directories are scanned.
         Directories specified with -idirafter options are scanned in left-to-right order.
     You can use -I to override a system header file, substituting your own version, since these directories are searched before the standard system header file directories. However, you should not use this option to add directories that contain vendor-supplied system header files; use -isystem for that.
     The -isystem and -idirafter options also mark the directory as a system directory, so that it gets the same special treatment that is applied to the standard system directories.
     If a standard system include directory, or a directory specified with -isystem, is also specified with -I, the -I option is ignored. The directory is still searched but as a system directory at its normal position in the system include chain. This is to ensure that GCC’s procedure to fix buggy system headers and the ordering for the #include_next directive are not inadvertently changed. If you really need to change the search order for system directories, use the -nostdinc and/or -isystem options.