A character constant within a preprocessing directive has the same numeric value as it has within any other expression.
Character constants in this context may have negative values (SPARC) (x86).
A file whose name is delimited by < > is searched for first in the directories named by the -I option, and then in the standard directory. The standard directory is /usr/include, unless the -YI option is used to specify a different default location.
A file whose name is delimited by quotes is searched for first in the directory of the source file that contains the #include, then in directories named by the -I option, and last in the standard directory.
If a file name enclosed in < > or double quotes begins with a / character, the file name is interpreted as a path name beginning in the root directory. The search for this file begins in the root directory only.
Quoted file names in include directives are supported.
Source file characters are mapped to their corresponding ASCII values.
The following pragmas are supported. See 2.8 Pragmas for more information.
align integer (variable[, variable])
does_not_read_global_data (funcname [, funcname])
does_not_return (funcname[, funcname])
does_not_write_global_data (funcname[, funcname])
error_messages (on|off|default, tag1[ tag2... tagn])
fini (f1[, f2..., fn])
init (f1[, f2..., fn])
inline (funcname[, funcname])
no_inline (funcname[, funcname])
no_side_effect (funcname[, funcname])
opt_level (funcname[, funcname])
rarely_called (funcname[, funcname])
redefine_extname old_extname new_extname
returns_new_memory (funcname[, funcname])
unknown_control_flow (name[, name])
weak (symbol1 [= symbol2])
These macros are always available from the environment.