Traditional miscellany#
Here are some things to be aware of when using the traditional preprocessor.
Preprocessing directives are recognized only when their leading
#
appears in the first column. There can be no whitespace between the beginning of the line and the#
, but whitespace can follow the#
.A true traditional C preprocessor does not recognize
#error
or#pragma
, and may not recognize#elif
. CPP supports all the directives in traditional mode that it supports in ISO mode, including extensions, with the exception that the effects of#pragma GCC poison
are undefined.__STDC__ is not defined.
If you use digraphs the behavior is undefined.
If a line that looks like a directive appears within macro arguments, the behavior is undefined.