String#byterindex

byterindex(substring, offset = self.bytesize) → integer or nil

byterindex(regexp, offset = self.bytesize) → integer or nil

static VALUE
rb_str_byterindex_m(int argc, VALUE *argv, VALUE str)
{
    VALUE sub;
    VALUE initpos;
    long pos, len = RSTRING_LEN(str);

    if (rb_scan_args(argc, argv, "11", &sub, &initpos) == 2) {
        pos = NUM2LONG(initpos);
        if (pos < 0 && (pos += len) < 0) {
            if (RB_TYPE_P(sub, T_REGEXP)) {
                rb_backref_set(Qnil);
            }
            return Qnil;
        }
        if (pos > len) pos = len;
    }
    else {
        pos = len;
    }

    str_ensure_byte_pos(str, pos);

    if (RB_TYPE_P(sub, T_REGEXP)) {
        if (rb_reg_search(sub, str, pos, 1) >= 0) {
            VALUE match = rb_backref_get();
            struct re_registers *regs = RMATCH_REGS(match);
            pos = BEG(0);
            return LONG2NUM(pos);
        }
    }
    else {
        StringValue(sub);
        pos = rb_str_byterindex(str, sub, pos);
        if (pos >= 0) return LONG2NUM(pos);
    }
    return Qnil;
}

Returns the Integer byte-based index of the last occurrence of the given substring, or nil if none found:

Example

'foo'.byterindex('f') # => 0
'foo'.byterindex('o') # => 2
'foo'.byterindex('oo') # => 1
'foo'.byterindex('ooo') # => nil

Returns the Integer byte-based index of the last match for the given Regexp regexp, or nil if none found:

Example

'foo'.byterindex(/f/) # => 0
'foo'.byterindex(/o/) # => 2
'foo'.byterindex(/oo/) # => 1
'foo'.byterindex(/ooo/) # => nil

The last match means starting at the possible last position, not the last of longest matches.

Example

'foo'.byterindex(/o+/) # => 2
$~ #=> #<MatchData "o">

To get the last longest match, needs to combine with negative lookbehind.

Example

'foo'.byterindex(/(?<!o)o+/) # => 1
$~ #=> #<MatchData "oo">

Or String#byteindex with negative lookforward.

Example

'foo'.byteindex(/o+(?!.*o)/) # => 1
$~ #=> #<MatchData "oo">

Integer argument offset, if given and non-negative, specifies the maximum starting byte-based position in the

Example

string to _end_ the search:

 'foo'.byterindex('o', 0) # => nil
 'foo'.byterindex('o', 1) # => 1
 'foo'.byterindex('o', 2) # => 2
 'foo'.byterindex('o', 3) # => 2

If offset is a negative Integer, the maximum starting position in the string to end the search is the sum of the string’s length and offset:

Example

'foo'.byterindex('o', -1) # => 2
'foo'.byterindex('o', -2) # => 1
'foo'.byterindex('o', -3) # => nil
'foo'.byterindex('o', -4) # => nil

If offset does not land on character (codepoint) boundary, IndexError is raised.

Related: String#byteindex.

Ruby version changes

3.2
- String#byteindex and String#byterindex have been added. [Feature #13110]

See also #byteindex #bytes #b #bytesize also in 4.1 · 4.0 · 3.4 · 3.2

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