class StringScanner
StringScanner provides for lexical scanning operations on a String. Here is an example of its usage:
s = StringScanner.new('This is an example string') s.eos? # -> false p s.scan(/\w+/) # -> "This" p s.scan(/\w+/) # -> nil p s.scan(/\s+/) # -> " " p s.scan(/\s+/) # -> nil p s.scan(/\w+/) # -> "is" s.eos? # -> false p s.scan(/\s+/) # -> " " p s.scan(/\w+/) # -> "an" p s.scan(/\s+/) # -> " " p s.scan(/\w+/) # -> "example" p s.scan(/\s+/) # -> " " p s.scan(/\w+/) # -> "string" s.eos? # -> true p s.scan(/\s+/) # -> nil p s.scan(/\w+/) # -> nil
Scanning a string means remembering the position of a scan pointer, which is just an index. The point of scanning is to move forward a bit at a time, so matches are sought after the scan pointer; usually immediately after it.
Given the string “test string”, here are the pertinent scan pointer positions:
t e s t s t r i n g 0 1 2 ... 1 0
When you scan for a pattern (a regular expression), the match must occur at the character after the scan pointer. If you use scan_until, then the match can occur anywhere after the scan pointer. In both cases, the scan pointer moves just beyond the last character of the match, ready to scan again from the next character onwards. This is demonstrated by the example above.
Method Categories¶ ↑
There are other methods besides the plain scanners. You can look ahead in the string without actually scanning. You can access the most recent match. You can modify the string being scanned, reset or terminate the scanner, find out or change the position of the scan pointer, skip ahead, and so on.
Advancing the Scan Pointer¶ ↑
Looking Ahead¶ ↑
Finding Where we Are¶ ↑
-
beginning_of_line? (#bol?)
Setting Where we Are¶ ↑
Match Data¶ ↑
Miscellaneous¶ ↑
There are aliases to several of the methods.
Public Class Methods
This method is defined for backward compatibility.
static VALUE strscan_s_mustc(VALUE self) { return self; }
Creates a new StringScanner object to scan
over the given string
. dup
argument is obsolete
and not used now.
static VALUE strscan_initialize(int argc, VALUE *argv, VALUE self) { struct strscanner *p; VALUE str, need_dup; p = check_strscan(self); rb_scan_args(argc, argv, "11", &str, &need_dup); StringValue(str); p->str = str; return self; }
Public Instance Methods
Appends str
to the string being scanned. This method does not
affect scan pointer.
s = StringScanner.new("Fri Dec 12 1975 14:39") s.scan(/Fri /) s << " +1000 GMT" s.string # -> "Fri Dec 12 1975 14:39 +1000 GMT" s.scan(/Dec/) # -> "Dec"
static VALUE strscan_concat(VALUE self, VALUE str) { struct strscanner *p; GET_SCANNER(self, p); StringValue(str); rb_str_append(p->str, str); return self; }
Return the n-th subgroup in the most recent match.
s = StringScanner.new("Fri Dec 12 1975 14:39") s.scan(/(\w+) (\w+) (\d+) /) # -> "Fri Dec 12 " s[0] # -> "Fri Dec 12 " s[1] # -> "Fri" s[2] # -> "Dec" s[3] # -> "12" s.post_match # -> "1975 14:39" s.pre_match # -> "" s.reset s.scan(/(?<wday>\w+) (?<month>\w+) (?<day>\d+) /) # -> "Fri Dec 12 " s[0] # -> "Fri Dec 12 " s[1] # -> "Fri" s[2] # -> "Dec" s[3] # -> "12" s[:wday] # -> "Fri" s[:month] # -> "Dec" s[:day] # -> "12" s.post_match # -> "1975 14:39" s.pre_match # -> ""
static VALUE strscan_aref(VALUE self, VALUE idx) { const char *name; struct strscanner *p; long i; GET_SCANNER(self, p); if (! MATCHED_P(p)) return Qnil; switch (TYPE(idx)) { case T_SYMBOL: name = rb_id2name(SYM2ID(idx)); goto name_to_backref; break; case T_STRING: name = StringValuePtr(idx); name_to_backref: i = name_to_backref_number(&(p->regs), p->regex, name, name + strlen(name)); break; default: i = NUM2LONG(idx); } if (i < 0) i += p->regs.num_regs; if (i < 0) return Qnil; if (i >= p->regs.num_regs) return Qnil; if (p->regs.beg[i] == -1) return Qnil; return extract_range(p, p->prev + p->regs.beg[i], p->prev + p->regs.end[i]); }
Returns true
iff the scan pointer is at the beginning of the
line.
s = StringScanner.new("test\ntest\n") s.bol? # => true s.scan(/te/) s.bol? # => false s.scan(/st\n/) s.bol? # => true s.terminate s.bol? # => true
static VALUE strscan_bol_p(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); if (CURPTR(p) > S_PEND(p)) return Qnil; if (p->curr == 0) return Qtrue; return (*(CURPTR(p) - 1) == '\n') ? Qtrue : Qfalse; }
Returns the character position of the scan pointer. In the 'reset' position, this value is zero. In the 'terminated' position (i.e. the string is exhausted), this value is the size of the string.
In short, it's a 0-based index into the string.
s = StringScanner.new("abcädeföghi") s.charpos # -> 0 s.scan_until(/ä/) # -> "abcä" s.pos # -> 5 s.charpos # -> 4
static VALUE strscan_get_charpos(VALUE self) { struct strscanner *p; VALUE substr; GET_SCANNER(self, p); substr = rb_funcall(p->str, id_byteslice, 2, INT2FIX(0), INT2NUM(p->curr)); return rb_str_length(substr); }
This returns the value that scan would return, without advancing the scan pointer. The match register is affected, though.
s = StringScanner.new("Fri Dec 12 1975 14:39") s.check /Fri/ # -> "Fri" s.pos # -> 0 s.matched # -> "Fri" s.check /12/ # -> nil s.matched # -> nil
Mnemonic: it “checks” to see whether a scan will return a value.
static VALUE strscan_check(VALUE self, VALUE re) { return strscan_do_scan(self, re, 0, 1, 1); }
This returns the value that scan_until would return, without advancing the scan pointer. The match register is affected, though.
s = StringScanner.new("Fri Dec 12 1975 14:39") s.check_until /12/ # -> "Fri Dec 12" s.pos # -> 0 s.matched # -> 12
Mnemonic: it “checks” to see whether a scan_until will return a value.
static VALUE strscan_check_until(VALUE self, VALUE re) { return strscan_do_scan(self, re, 0, 1, 0); }
Appends str
to the string being scanned. This method does not
affect scan pointer.
s = StringScanner.new("Fri Dec 12 1975 14:39") s.scan(/Fri /) s << " +1000 GMT" s.string # -> "Fri Dec 12 1975 14:39 +1000 GMT" s.scan(/Dec/) # -> "Dec"
static VALUE strscan_concat(VALUE self, VALUE str) { struct strscanner *p; GET_SCANNER(self, p); StringValue(str); rb_str_append(p->str, str); return self; }
Returns true
if the scan pointer is at the end of the string.
s = StringScanner.new('test string') p s.eos? # => false s.scan(/test/) p s.eos? # => false s.terminate p s.eos? # => true
static VALUE strscan_eos_p(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); return EOS_P(p) ? Qtrue : Qfalse; }
Looks ahead to see if the pattern
exists
anywhere in the string, without advancing the scan pointer. This
predicates whether a scan_until will return a
value.
s = StringScanner.new('test string') s.exist? /s/ # -> 3 s.scan /test/ # -> "test" s.exist? /s/ # -> 2 s.exist? /e/ # -> nil
static VALUE strscan_exist_p(VALUE self, VALUE re) { return strscan_do_scan(self, re, 0, 0, 0); }
Scans one byte and returns it. This method is not multibyte character sensitive. See also: getch.
s = StringScanner.new('ab') s.get_byte # => "a" s.get_byte # => "b" s.get_byte # => nil $KCODE = 'EUC' s = StringScanner.new("\244\242") s.get_byte # => "\244" s.get_byte # => "\242" s.get_byte # => nil
static VALUE strscan_get_byte(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); CLEAR_MATCH_STATUS(p); if (EOS_P(p)) return Qnil; p->prev = p->curr; p->curr++; MATCHED(p); adjust_registers_to_matched(p); return extract_range(p, p->prev + p->regs.beg[0], p->prev + p->regs.end[0]); }
Scans one character and returns it. This method is multibyte character sensitive.
s = StringScanner.new("ab") s.getch # => "a" s.getch # => "b" s.getch # => nil $KCODE = 'EUC' s = StringScanner.new("\244\242") s.getch # => "\244\242" # Japanese hira-kana "A" in EUC-JP s.getch # => nil
static VALUE strscan_getch(VALUE self) { struct strscanner *p; long len; GET_SCANNER(self, p); CLEAR_MATCH_STATUS(p); if (EOS_P(p)) return Qnil; len = rb_enc_mbclen(CURPTR(p), S_PEND(p), rb_enc_get(p->str)); if (p->curr + len > S_LEN(p)) { len = S_LEN(p) - p->curr; } p->prev = p->curr; p->curr += len; MATCHED(p); adjust_registers_to_matched(p); return extract_range(p, p->prev + p->regs.beg[0], p->prev + p->regs.end[0]); }
Returns a string that represents the StringScanner object, showing:
-
the current position
-
the size of the string
-
the characters surrounding the scan pointer
s = ::new(“Fri Dec 12 1975 14:39”) s.inspect # -> '#<StringScanner 0/21 @ “Fri D…”>' s.scan_until /12/ # -> “Fri Dec 12” s.inspect # -> '#<StringScanner 10/21 “…ec 12” @ “ 1975…”>'
static VALUE strscan_inspect(VALUE self) { struct strscanner *p; VALUE a, b; p = check_strscan(self); if (NIL_P(p->str)) { a = rb_sprintf("#<%"PRIsVALUE" (uninitialized)>", rb_obj_class(self)); return infect(a, p); } if (EOS_P(p)) { a = rb_sprintf("#<%"PRIsVALUE" fin>", rb_obj_class(self)); return infect(a, p); } if (p->curr == 0) { b = inspect2(p); a = rb_sprintf("#<%"PRIsVALUE" %ld/%ld @ %"PRIsVALUE">", rb_obj_class(self), p->curr, S_LEN(p), b); return infect(a, p); } a = inspect1(p); b = inspect2(p); a = rb_sprintf("#<%"PRIsVALUE" %ld/%ld %"PRIsVALUE" @ %"PRIsVALUE">", rb_obj_class(self), p->curr, S_LEN(p), a, b); return infect(a, p); }
Tests whether the given pattern
is matched from the current
scan pointer. Returns the length of the match, or nil
. The
scan pointer is not advanced.
s = StringScanner.new('test string') p s.match?(/\w+/) # -> 4 p s.match?(/\w+/) # -> 4 p s.match?(/\s+/) # -> nil
static VALUE strscan_match_p(VALUE self, VALUE re) { return strscan_do_scan(self, re, 0, 0, 1); }
Returns the last matched string.
s = StringScanner.new('test string') s.match?(/\w+/) # -> 4 s.matched # -> "test"
static VALUE strscan_matched(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); if (! MATCHED_P(p)) return Qnil; return extract_range(p, p->prev + p->regs.beg[0], p->prev + p->regs.end[0]); }
Returns true
iff the last match was successful.
s = StringScanner.new('test string') s.match?(/\w+/) # => 4 s.matched? # => true s.match?(/\d+/) # => nil s.matched? # => false
static VALUE strscan_matched_p(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); return MATCHED_P(p) ? Qtrue : Qfalse; }
Returns the size of the most recent match (see matched), or
nil
if there was no recent match.
s = StringScanner.new('test string') s.check /\w+/ # -> "test" s.matched_size # -> 4 s.check /\d+/ # -> nil s.matched_size # -> nil
static VALUE strscan_matched_size(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); if (! MATCHED_P(p)) return Qnil; return INT2NUM(p->regs.end[0] - p->regs.beg[0]); }
Extracts a string corresponding to string[pos,len]
, without
advancing the scan pointer.
s = StringScanner.new('test string') s.peek(7) # => "test st" s.peek(7) # => "test st"
static VALUE strscan_peek(VALUE self, VALUE vlen) { struct strscanner *p; long len; GET_SCANNER(self, p); len = NUM2LONG(vlen); if (EOS_P(p)) return infect(str_new(p, "", 0), p); if (p->curr + len > S_LEN(p)) len = S_LEN(p) - p->curr; return extract_beg_len(p, p->curr, len); }
Returns the byte position of the scan pointer. In the 'reset' position, this value is zero. In the 'terminated' position (i.e. the string is exhausted), this value is the bytesize of the string.
In short, it's a 0-based index into bytes of the string.
s = StringScanner.new('test string') s.pos # -> 0 s.scan_until /str/ # -> "test str" s.pos # -> 8 s.terminate # -> #<StringScanner fin> s.pos # -> 11
static VALUE strscan_get_pos(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); return INT2FIX(p->curr); }
Set the byte position of the scan pointer.
s = StringScanner.new('test string') s.pos = 7 # -> 7 s.rest # -> "ring"
static VALUE strscan_set_pos(VALUE self, VALUE v) { struct strscanner *p; long i; GET_SCANNER(self, p); i = NUM2INT(v); if (i < 0) i += S_LEN(p); if (i < 0) rb_raise(rb_eRangeError, "index out of range"); if (i > S_LEN(p)) rb_raise(rb_eRangeError, "index out of range"); p->curr = i; return INT2NUM(i); }
Returns the byte position of the scan pointer. In the 'reset' position, this value is zero. In the 'terminated' position (i.e. the string is exhausted), this value is the bytesize of the string.
In short, it's a 0-based index into bytes of the string.
s = StringScanner.new('test string') s.pos # -> 0 s.scan_until /str/ # -> "test str" s.pos # -> 8 s.terminate # -> #<StringScanner fin> s.pos # -> 11
static VALUE strscan_get_pos(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); return INT2FIX(p->curr); }
Set the byte position of the scan pointer.
s = StringScanner.new('test string') s.pos = 7 # -> 7 s.rest # -> "ring"
static VALUE strscan_set_pos(VALUE self, VALUE v) { struct strscanner *p; long i; GET_SCANNER(self, p); i = NUM2INT(v); if (i < 0) i += S_LEN(p); if (i < 0) rb_raise(rb_eRangeError, "index out of range"); if (i > S_LEN(p)) rb_raise(rb_eRangeError, "index out of range"); p->curr = i; return INT2NUM(i); }
Return the post-match (in the regular expression sense) of the last scan.
s = StringScanner.new('test string') s.scan(/\w+/) # -> "test" s.scan(/\s+/) # -> " " s.pre_match # -> "test" s.post_match # -> "string"
static VALUE strscan_post_match(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); if (! MATCHED_P(p)) return Qnil; return extract_range(p, p->prev + p->regs.end[0], S_LEN(p)); }
Return the pre-match (in the regular expression sense) of the last scan.
s = StringScanner.new('test string') s.scan(/\w+/) # -> "test" s.scan(/\s+/) # -> " " s.pre_match # -> "test" s.post_match # -> "string"
static VALUE strscan_pre_match(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); if (! MATCHED_P(p)) return Qnil; return extract_range(p, 0, p->prev + p->regs.beg[0]); }
Reset the scan pointer (index 0) and clear matching data.
static VALUE strscan_reset(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); p->curr = 0; CLEAR_MATCH_STATUS(p); return self; }
Returns the “rest” of the string (i.e. everything after the scan pointer).
If there is no more data (eos? = true), it returns
""
.
static VALUE strscan_rest(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); if (EOS_P(p)) { return infect(str_new(p, "", 0), p); } return extract_range(p, p->curr, S_LEN(p)); }
Returns true iff there is more data in the string. See eos?. This method is obsolete; use eos? instead.
s = StringScanner.new('test string') s.eos? # These two s.rest? # are opposites.
static VALUE strscan_rest_p(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); return EOS_P(p) ? Qfalse : Qtrue; }
s.rest_size
is equivalent to s.rest.size
.
static VALUE strscan_rest_size(VALUE self) { struct strscanner *p; long i; GET_SCANNER(self, p); if (EOS_P(p)) { return INT2FIX(0); } i = S_LEN(p) - p->curr; return INT2FIX(i); }
s.restsize
is equivalent to s.rest_size
. This
method is obsolete; use rest_size instead.
static VALUE strscan_restsize(VALUE self) { rb_warning("StringScanner#restsize is obsolete; use #rest_size instead"); return strscan_rest_size(self); }
Tries to match with pattern
at the current position. If
there's a match, the scanner advances the “scan pointer” and returns
the matched string. Otherwise, the scanner returns nil
.
s = StringScanner.new('test string') p s.scan(/\w+/) # -> "test" p s.scan(/\w+/) # -> nil p s.scan(/\s+/) # -> " " p s.scan(/\w+/) # -> "string" p s.scan(/./) # -> nil
static VALUE strscan_scan(VALUE self, VALUE re) { return strscan_do_scan(self, re, 1, 1, 1); }
Tests whether the given pattern
is matched from the current
scan pointer. Advances the scan pointer if advance_pointer_p
is true. Returns the matched string if return_string_p
is
true. The match register is affected.
“full” means “#scan with full parameters”.
static VALUE strscan_scan_full(VALUE self, VALUE re, VALUE s, VALUE f) { return strscan_do_scan(self, re, RTEST(s), RTEST(f), 1); }
Scans the string until the pattern
is matched.
Returns the substring up to and including the end of the match, advancing
the scan pointer to that location. If there is no match, nil
is returned.
s = StringScanner.new("Fri Dec 12 1975 14:39") s.scan_until(/1/) # -> "Fri Dec 1" s.pre_match # -> "Fri Dec " s.scan_until(/XYZ/) # -> nil
static VALUE strscan_scan_until(VALUE self, VALUE re) { return strscan_do_scan(self, re, 1, 1, 0); }
Scans the string until the pattern
is matched.
Advances the scan pointer if advance_pointer_p
, otherwise not.
Returns the matched string if return_string_p
is true,
otherwise returns the number of bytes advanced. This method does affect the
match register.
static VALUE strscan_search_full(VALUE self, VALUE re, VALUE s, VALUE f) { return strscan_do_scan(self, re, RTEST(s), RTEST(f), 0); }
Attempts to skip over the given pattern
beginning with the
scan pointer. If it matches, the scan pointer is advanced to the end of the
match, and the length of the match is returned. Otherwise,
nil
is returned.
It's similar to scan, but without returning the matched string.
s = StringScanner.new('test string') p s.skip(/\w+/) # -> 4 p s.skip(/\w+/) # -> nil p s.skip(/\s+/) # -> 1 p s.skip(/\w+/) # -> 6 p s.skip(/./) # -> nil
static VALUE strscan_skip(VALUE self, VALUE re) { return strscan_do_scan(self, re, 1, 0, 1); }
Advances the scan pointer until pattern
is matched and
consumed. Returns the number of bytes advanced, or nil
if no
match was found.
Look ahead to match pattern
, and advance the scan pointer to
the end of the match. Return the number of characters advanced,
or nil
if the match was unsuccessful.
It's similar to scan_until, but without returning the intervening string.
s = StringScanner.new("Fri Dec 12 1975 14:39") s.skip_until /12/ # -> 10 s #
static VALUE strscan_skip_until(VALUE self, VALUE re) { return strscan_do_scan(self, re, 1, 0, 0); }
Returns the string being scanned.
static VALUE strscan_get_string(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); return p->str; }
Changes the string being scanned to str
and resets the
scanner. Returns str
.
static VALUE strscan_set_string(VALUE self, VALUE str) { struct strscanner *p = check_strscan(self); StringValue(str); p->str = str; p->curr = 0; CLEAR_MATCH_STATUS(p); return str; }
Set the scan pointer to the end of the string and clear matching data.
static VALUE strscan_terminate(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); p->curr = S_LEN(p); CLEAR_MATCH_STATUS(p); return self; }
Set the scan pointer to the previous position. Only one previous position is remembered, and it changes with each scanning operation.
s = StringScanner.new('test string') s.scan(/\w+/) # => "test" s.unscan s.scan(/../) # => "te" s.scan(/\d/) # => nil s.unscan # ScanError: unscan failed: previous match record not exist
static VALUE strscan_unscan(VALUE self) { struct strscanner *p; GET_SCANNER(self, p); if (! MATCHED_P(p)) rb_raise(ScanError, "unscan failed: previous match record not exist"); p->curr = p->prev; CLEAR_MATCH_STATUS(p); return self; }
Private Instance Methods
Duplicates a StringScanner object.
static VALUE strscan_init_copy(VALUE vself, VALUE vorig) { struct strscanner *self, *orig; self = check_strscan(vself); orig = check_strscan(vorig); if (self != orig) { self->flags = orig->flags; self->str = orig->str; self->prev = orig->prev; self->curr = orig->curr; onig_region_copy(&self->regs, &orig->regs); } return vself; }