diff options
Diffstat (limited to 'contrib/gcc/doc/cpp.texi')
| -rw-r--r-- | contrib/gcc/doc/cpp.texi | 37 |
1 files changed, 20 insertions, 17 deletions
diff --git a/contrib/gcc/doc/cpp.texi b/contrib/gcc/doc/cpp.texi index 8e829d8..39e6a28 100644 --- a/contrib/gcc/doc/cpp.texi +++ b/contrib/gcc/doc/cpp.texi @@ -830,11 +830,22 @@ version of GCC in use. You can add to this list with the @option{-I@var{dir}} command line option. All the directories named by @option{-I} are searched, in -left-to-right order, @emph{before} the default directories. You can -also prevent GCC from searching any of the default directories with the -@option{-nostdinc} option. This is useful when you are compiling an +left-to-right order, @emph{before} the default directories. The only +exception is when @file{dir} is already searched by default. In +this case, the option is ignored and the search order for system +directories remains unchanged. + +Duplicate directories are removed from the quote and bracket search +chains before the two chains are merged to make the final search chain. +Thus, it is possible for a directory to occur twice in the final search +chain if it was specified in both the quote and bracket chains. + +You can prevent GCC from searching any of the default directories with +the @option{-nostdinc} option. This is useful when you are compiling an operating system kernel or some other program that does not use the standard C library facilities, or the standard C library itself. +@option{-I} options are not ignored as described above when +@option{-nostdinc} is in effect. GCC looks for headers requested with @code{@w{#include "@var{file}"}} first in the directory containing the current file, then in the same @@ -843,12 +854,6 @@ For example, if @file{/usr/include/sys/stat.h} contains @code{@w{#include "types.h"}}, GCC looks for @file{types.h} first in @file{/usr/include/sys}, then in its usual search path. -If you name a search directory with @option{-I@var{dir}} that is also a -system include directory, the @option{-I} wins; the directory will be -searched according to the @option{-I} ordering, and it will not be -treated as a system include directory. GCC will warn you when a system -include directory is hidden in this way. - @samp{#line} (@pxref{Line Control}) does not change GCC's idea of the directory containing the current file. @@ -1081,8 +1086,8 @@ found in that directory will be considered system headers. All directories named by @option{-isystem} are searched @emph{after} all directories named by @option{-I}, no matter what their order was on the command line. If the same directory is named by both @option{-I} and -@option{-isystem}, @option{-I} wins; it is as if the @option{-isystem} option -had never been specified at all. GCC warns you when this happens. +@option{-isystem}, the @option{-I} option is ignored. GCC provides an +informative message when this occurs if @option{-v} is used. @findex #pragma GCC system_header There is also a directive, @code{@w{#pragma GCC system_header}}, which @@ -1815,9 +1820,7 @@ conformance to the C Standard. GNU CPP follows the host convention when processing system header files, but when processing user files @code{__STDC__} is always 1. This has been reported to cause problems; for instance, some versions of Solaris provide X Windows headers that -expect @code{__STDC__} to be either undefined or 1. You may be able to -work around this sort of problem by using an @option{-I} option to -cancel treatment of those headers as system headers. @xref{Invocation}. +expect @code{__STDC__} to be either undefined or 1. @xref{Invocation}. @item __STDC_VERSION__ This macro expands to the C Standard's version number, a long integer @@ -3733,9 +3736,9 @@ Here are a few more obsolete features. @item Attempting to paste two tokens which together do not form a valid preprocessing token. -The preprocessor currently warns about this and outputs the two tokens -adjacently, which is probably the behavior the programmer intends. It -may not work in future, though. +The preprocessor currently warns about this, and the resulting +preprocessed output is undefined. The tokens remain distinct if the +preprocessor is being used directly by the compiler front end. Most of the time, when you get this warning, you will find that @samp{##} is being used superstitiously, to guard against whitespace appearing |
