To compile, match, or search for a given regular expression, you must supply a pattern buffer. A pattern buffer holds one compiled regular expression.(4)
You can have several different pattern buffers simultaneously, each holding a compiled pattern for a different regular expression.
`regex.h' defines the pattern buffer struct
as follows:
/* Space that holds the compiled pattern. It is declared as `unsigned char *' because its elements are sometimes used as array indexes. */ unsigned char *buffer; /* Number of bytes to which `buffer' points. */ unsigned long allocated; /* Number of bytes actually used in `buffer'. */ unsigned long used; /* Syntax setting with which the pattern was compiled. */ reg_syntax_t syntax; /* Pointer to a fastmap, if any, otherwise zero. re_search uses the fastmap, if there is one, to skip over impossible starting points for matches. */ char *fastmap; /* Either a translate table to apply to all characters before comparing them, or zero for no translation. The translation is applied to a pattern when it is compiled and to a string when it is matched. */ char *translate; /* Number of subexpressions found by the compiler. */ size_t re_nsub; /* Zero if this pattern cannot match the empty string, one else. Well, in truth it's used only in `re_search_2', to see whether or not we should use the fastmap, so we don't set this absolutely perfectly; see `re_compile_fastmap' (the `duplicate' case). */ unsigned can_be_null : 1; /* If REGS_UNALLOCATED, allocate space in the `regs' structure for `max (RE_NREGS, re_nsub + 1)' groups. If REGS_REALLOCATE, reallocate space if necessary. If REGS_FIXED, use what's there. */ #define REGS_UNALLOCATED 0 #define REGS_REALLOCATE 1 #define REGS_FIXED 2 unsigned regs_allocated : 2; /* Set to zero when `regex_compile' compiles a pattern; set to one by `re_compile_fastmap' if it updates the fastmap. */ unsigned fastmap_accurate : 1; /* If set, `re_match_2' does not return information about subexpressions. */ unsigned no_sub : 1; /* If set, a beginning-of-line anchor doesn't match at the beginning of the string. */ unsigned not_bol : 1; /* Similarly for an end-of-line anchor. */ unsigned not_eol : 1; /* If true, an anchor at a newline matches. */ unsigned newline_anchor : 1;
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