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Diffstat (limited to 'gcc/doc/cpp.texi')
| -rw-r--r-- | gcc/doc/cpp.texi | 24 |
1 files changed, 16 insertions, 8 deletions
diff --git a/gcc/doc/cpp.texi b/gcc/doc/cpp.texi index 260efdcf945..7ba498dab5f 100644 --- a/gcc/doc/cpp.texi +++ b/gcc/doc/cpp.texi @@ -3508,17 +3508,25 @@ same column as it did in the original source file. @item The numeric value of character constants in preprocessor expressions. -The preprocessor and compiler interpret character constants in the same -way; escape sequences such as @samp{\a} are given the values they would -have on the target machine. +The preprocessor and compiler interpret character constants in the +same way; i.e.@: escape sequences such as @samp{\a} are given the +values they would have on the target machine. Multi-character character constants are interpreted a character at a time, shifting the previous result left by the number of bits per -character on the host, and adding the new character. For example, 'ab' -on an 8-bit host would be interpreted as @w{'a' * 256 + 'b'}. If there -are more characters in the constant than can fit in the widest native -integer type on the host, usually a @code{long}, the excess characters -are ignored and a diagnostic is given. +target character and adding the sign-extended value of the new +character. They have type @code{int}, and are treated as signed +regardless of whether single characters are signed or not. If there +are more characters in the constant than would fit in the target +@code{int}, a diagnostic is given, and the excess leading characters +are ignored. This methodology is not fully compatible with versions +3.1 and earlier of GCC, which used a confusing and inconsistent +valuation technique. + +For example, 'ab' for a target with an 8-bit @code{char} would be +interpreted as @w{'a' * 256 + 'b'}, and 'a\234' as @w{'a' * 256 + +'\234'}. GCC 3.1 and earlier would give a different value for the +latter example, probably @w{'a' * 256 + (unsigned char) '\234'}. @item Source file inclusion. |