The mapping of physical source file multi-byte characters to the
execution character set.
Currently, CPP requires its input to be ASCII or UTF-8. The execution
character set may be controlled by the user, with the
-ftarget-charset and -ftarget-wide-charset options.
Identifier characters.
The C and C++ standards allow identifiers to be composed of _
and the alphanumeric characters. C++ and C99 also allow universal
character names (not implemented in GCC), and C99 further permits
implementation-defined characters.
GCC allows the $ character in identifiers as an extension for
most targets. This is true regardless of the std= switch,
since this extension cannot conflict with standards-conforming
programs. When preprocessing assembler, however, dollars are not
identifier characters by default.
Currently the targets that by default do not permit $ are AVR,
IP2K, MMIX, MIPS Irix 3, ARM aout, and PowerPC targets for the AIX and
BeOS operating systems.
You can override the default with -fdollars-in-identifiers or
fno-dollars-in-identifiers.
Non-empty sequences of whitespace characters.
In textual output, each whitespace sequence is collapsed to a single
space. For aesthetic reasons, the first token on each non-directive
line of output is preceded with sufficient spaces that it appears in the
same column as it did in the original source file.
The numeric value of character constants in preprocessor expressions.
The preprocessor and compiler interpret character constants in the
same way; i.e. escape sequences such as \a are given the
values they would have on the target machine.
The compiler values a multi-character character constant a character
at a time, shifting the previous value left by the number of bits per
target character, and then or-ing in the bit-pattern of the new
character truncated to the width of a target character. The final
bit-pattern is given type int, and is therefore signed,
regardless of whether single characters are signed or not (a slight
change from versions 3.1 and earlier of GCC). If there are more
characters in the constant than would fit in the target int the
compiler issues a warning, and the excess leading characters are
ignored.
For example, 'ab' for a target with an 8-bit char would be
interpreted as (int) ((unsigned char) 'a' * 256 + (unsigned char)
'b'), and '\234a' as (int) ((unsigned char) '\234' * 256 + (unsigned
char) 'a').
Source file inclusion.
For a discussion on how the preprocessor locates header files,
Section 2.2 Include Operation.
Interpretation of the filename resulting from a macro-expanded
#include directive.
Section 2.5 Computed Includes.
Treatment of a #pragma directive that after macro-expansion
results in a standard pragma.
No macro expansion occurs on any #pragma directive line, so the
question does not arise.
Note that GCC does not yet implement any of the standard
pragmas.
