This is how CPP behaves in all the cases which the C standard describes as implementation-defined. This term means that the implementation is free to do what it likes, but must document its choice and stick to it.
Currently, GNU cpp only supports character sets that are strict supersets of ASCII, and performs no translation of 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 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
compiler issues a warning, and the excess leading characters are
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').
For a discussion on how the preprocessor locates header files, Include Operation.
See Computed Includes.
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.