A syntax table is an array indexed by the characters in your
character set. In the ASCII encoding, therefore, a syntax table
has 256 elements. Regex always uses a
char * variable
re_syntax_table as its syntax table. In some cases, it
initializes this variable and in others it expects you to initialize it.
SYNTAX_TABLEboth undefined, then Regex allocates
re_syntax_tableand initializes an element i either to
Sword(which it defines) if i is a letter, number, or ‘_’, or to zero if it's not.
SYNTAX_TABLEdefined, then Regex expects you to define a
re_syntax_tableto be a valid syntax table.