class StringIO

IO streams for strings, with access similar to IO; see IO.

About the Examples¶ ↑

Examples on this page assume that StringIO has been required:

require 'stringio'

Constants

MAX_LENGTH: Maximum length that a StringIO instance can hold
VERSION: The version string

Public Class Methods

new(string = '', mode = 'r+') → new_stringio

Note that mode defaults to 'r' if string is frozen.

Returns a new StringIO instance formed from string and mode; see Access Modes:

strio = StringIO.new # => #<StringIO>
strio.close

The instance should be closed when no longer needed.

Related: StringIO.open (accepts block; closes automatically).

static VALUE
strio_initialize(int argc, VALUE *argv, VALUE self)
{
    struct StringIO *ptr = check_strio(self);

    if (!ptr) {
        DATA_PTR(self) = ptr = strio_alloc();
    }
    rb_call_super(0, 0);
    return strio_init(argc, argv, ptr, self);
}

open(string = '', mode = 'r+') {|strio| ... }

Note that mode defaults to 'r' if string is frozen.

Creates a new StringIO instance formed from string and mode; see Access Modes.

With no block, returns the new instance:

strio = StringIO.open # => #<StringIO>

With a block, calls the block with the new instance and returns the block’s value; closes the instance on block exit.

StringIO.open {|strio| p strio }
# => #<StringIO>

Related: StringIO.new.

static VALUE
strio_s_open(int argc, VALUE *argv, VALUE klass)
{
    VALUE obj = rb_class_new_instance_kw(argc, argv, klass, RB_PASS_CALLED_KEYWORDS);
    if (!rb_block_given_p()) return obj;
    return rb_ensure(rb_yield, obj, strio_finalize, obj);
}

Public Instance Methods

binmode → self

Sets the data mode in self to binary mode; see Data Mode.

static VALUE
strio_binmode(VALUE self)
{
    struct StringIO *ptr = StringIO(self);
    rb_encoding *enc = rb_ascii8bit_encoding();

    ptr->enc = enc;
    if (WRITABLE(self)) {
        rb_enc_associate(ptr->string, enc);
    }
    return self;
}

close → nil

Closes self for both reading and writing.

Raises IOError if reading or writing is attempted.

static VALUE
strio_close(VALUE self)
{
    StringIO(self);
    RBASIC(self)->flags &= ~STRIO_READWRITE;
    return Qnil;
}

close_read → nil

Closes self for reading; closed-write setting remains unchanged.

Raises IOError if reading is attempted.

static VALUE
strio_close_read(VALUE self)
{
    struct StringIO *ptr = StringIO(self);
    if (!(ptr->flags & FMODE_READABLE)) {
        rb_raise(rb_eIOError, "closing non-duplex IO for reading");
    }
    RBASIC(self)->flags &= ~STRIO_READABLE;
    return Qnil;
}

close_write → nil

Closes self for writing; closed-read setting remains unchanged.

Raises IOError if writing is attempted.

static VALUE
strio_close_write(VALUE self)
{
    struct StringIO *ptr = StringIO(self);
    if (!(ptr->flags & FMODE_WRITABLE)) {
        rb_raise(rb_eIOError, "closing non-duplex IO for writing");
    }
    RBASIC(self)->flags &= ~STRIO_WRITABLE;
    return Qnil;
}

closed? → true or false

Returns true if self is closed for both reading and writing, false otherwise.

static VALUE
strio_closed(VALUE self)
{
    StringIO(self);
    if (!CLOSED(self)) return Qfalse;
    return Qtrue;
}

closed_read? → true or false

Returns true if self is closed for reading, false otherwise.

static VALUE
strio_closed_read(VALUE self)
{
    StringIO(self);
    if (READABLE(self)) return Qfalse;
    return Qtrue;
}

closed_write? → true or false

Returns true if self is closed for writing, false otherwise.

static VALUE
strio_closed_write(VALUE self)
{
    StringIO(self);
    if (WRITABLE(self)) return Qfalse;
    return Qtrue;
}

each

Also aliased as: each_line

each_byte {|byte| ... } → self

With a block given, calls the block with each remaining byte in the stream; see Byte IO.

With no block given, returns an enumerator.

static VALUE
strio_each_byte(VALUE self)
{
    struct StringIO *ptr;

    RETURN_ENUMERATOR(self, 0, 0);

    while ((ptr = strio_to_read(self)) != NULL) {
        char c = RSTRING_PTR(ptr->string)[ptr->pos++];
        rb_yield(CHR2FIX(c));
    }
    return self;
}

each_char {|c| ... } → self

With a block given, calls the block with each remaining character in the stream; see Character IO.

With no block given, returns an enumerator.

static VALUE
strio_each_char(VALUE self)
{
    VALUE c;

    RETURN_ENUMERATOR(self, 0, 0);

    while (!NIL_P(c = strio_getc(self))) {
        rb_yield(c);
    }
    return self;
}

each_codepoint {|codepoint| ... } → self

With a block given, calls the block with each remaining codepoint in the stream; see Codepoint IO.

With no block given, returns an enumerator.

static VALUE
strio_each_codepoint(VALUE self)
{
    struct StringIO *ptr;
    rb_encoding *enc;
    unsigned int c;
    int n;

    RETURN_ENUMERATOR(self, 0, 0);

    ptr = readable(self);
    enc = get_enc(ptr);
    while ((ptr = strio_to_read(self)) != NULL) {
        c = rb_enc_codepoint_len(RSTRING_PTR(ptr->string)+ptr->pos,
                                 RSTRING_END(ptr->string), &n, enc);
        ptr->pos += n;
        rb_yield(UINT2NUM(c));
    }
    return self;
}

each_line(sep = $/, chomp: false) {|line| ... } → self

each_line(limit, chomp: false) {|line| ... } → self

each_line(sep, limit, chomp: false) {|line| ... } → self

Calls the block with each remaining line read from the stream; does nothing if already at end-of-file; returns self. See Line IO.

Alias for: each

eof

Also aliased as: eof?

eof? → true or false

Returns true if positioned at end-of-stream, false otherwise; see Position.

Raises IOError if the stream is not opened for reading.

Alias for: eof

external_encoding → encoding

Returns the Encoding object that represents the encoding of the file. If the stream is write mode and no encoding is specified, returns nil.

static VALUE
strio_external_encoding(VALUE self)
{
    struct StringIO *ptr = StringIO(self);
    return rb_enc_from_encoding(get_enc(ptr));
}

fcntl (*args)

Raises NotImplementedError.

static VALUE
strio_unimpl(int argc, VALUE *argv, VALUE self)
{
    StringIO(self);
    rb_notimplement();

    UNREACHABLE;
}

fileno ()

Returns nil. Just for compatibility to IO.

static VALUE
strio_nil(VALUE self)
{
    StringIO(self);
    return Qnil;
}

flush ()

Returns an object itself. Just for compatibility to IO.

static VALUE
strio_self(VALUE self)
{
    StringIO(self);
    return self;
}

fsync ()

Returns 0. Just for compatibility to IO.

static VALUE
strio_0(VALUE self)
{
    StringIO(self);
    return INT2FIX(0);
}

getbyte → byte or nil

Reads and returns the next 8-bit byte from the stream; see Byte IO.

static VALUE
strio_getbyte(VALUE self)
{
    struct StringIO *ptr = readable(self);
    int c;
    if (NIL_P(ptr->string) || ptr->pos >= RSTRING_LEN(ptr->string)) {
        return Qnil;
    }
    c = RSTRING_PTR(ptr->string)[ptr->pos++];
    return CHR2FIX(c);
}

getc → character or nil

Reads and returns the next character from the stream; see Character IO.

static VALUE
strio_getc(VALUE self)
{
    struct StringIO *ptr = readable(self);
    rb_encoding *enc = get_enc(ptr);
    VALUE str = ptr->string;
    long pos = ptr->pos;
    int len;
    char *p;

    if (NIL_P(str) || pos >= RSTRING_LEN(str)) {
        return Qnil;
    }
    p = RSTRING_PTR(str)+pos;
    len = rb_enc_mbclen(p, RSTRING_END(str), enc);
    ptr->pos += len;
    return enc_subseq(str, pos, len, enc);
}

gets(sep = $/, chomp: false) → string or nil

gets(limit, chomp: false) → string or nil

gets(sep, limit, chomp: false) → string or nil

Reads and returns a line from the stream; assigns the return value to $_; see Line IO.

static VALUE
strio_gets(int argc, VALUE *argv, VALUE self)
{
    struct StringIO *ptr = readable(self);
    struct getline_arg arg;
    VALUE str;

    if (prepare_getline_args(ptr, &arg, argc, argv)->limit == 0) {
        if (NIL_P(ptr->string)) return Qnil;
        return rb_enc_str_new(0, 0, get_enc(ptr));
    }

    str = strio_getline(&arg, ptr);
    rb_lastline_set(str);
    return str;
}

internal_encoding → encoding

Returns the Encoding of the internal string if conversion is specified. Otherwise returns nil.

static VALUE
strio_internal_encoding(VALUE self)
{
    return Qnil;
}

isatty ()

Returns false. Just for compatibility to IO.

static VALUE
strio_false(VALUE self)
{
    StringIO(self);
    return Qfalse;
}

Also aliased as: tty?

length → integer

Returns the size of the buffer string.

Alias for: size

lineno → current_line_number

Returns the current line number in self; see Line Number.

static VALUE
strio_get_lineno(VALUE self)
{
    return LONG2NUM(StringIO(self)->lineno);
}

lineno = new_line_number → new_line_number

Sets the current line number in self to the given new_line_number; see Line Number.

static VALUE
strio_set_lineno(VALUE self, VALUE lineno)
{
    StringIO(self)->lineno = NUM2LONG(lineno);
    return lineno;
}

pid ()

Returns nil. Just for compatibility to IO.

static VALUE
strio_nil(VALUE self)
{
    StringIO(self);
    return Qnil;
}

pos → stream_position

Returns the current position (in bytes); see Position.

static VALUE
strio_get_pos(VALUE self)
{
    return LONG2NUM(StringIO(self)->pos);
}

pos = new_position → new_position

Sets the current position (in bytes); see Position.

static VALUE
strio_set_pos(VALUE self, VALUE pos)
{
    struct StringIO *ptr = StringIO(self);
    long p = NUM2LONG(pos);
    if (p < 0) {
        error_inval(0);
    }
    ptr->pos = p;
    return pos;
}

pread(maxlen, offset) → string

pread(maxlen, offset, out_string) → string

See IO#pread.

static VALUE
strio_pread(int argc, VALUE *argv, VALUE self)
{
    VALUE rb_len, rb_offset, rb_buf;
    rb_scan_args(argc, argv, "21", &rb_len, &rb_offset, &rb_buf);
    long len = NUM2LONG(rb_len);
    long offset = NUM2LONG(rb_offset);

    if (len < 0) {
        rb_raise(rb_eArgError, "negative string size (or size too big): %" PRIsVALUE, rb_len);
    }

    if (len == 0) {
        if (NIL_P(rb_buf)) {
            return rb_str_new("", 0);
        }
        return rb_buf;
    }

    if (offset < 0) {
        rb_syserr_fail_str(EINVAL, rb_sprintf("pread: Invalid offset argument: %" PRIsVALUE, rb_offset));
    }

    struct StringIO *ptr = readable(self);

    if (offset >= RSTRING_LEN(ptr->string)) {
        rb_eof_error();
    }

    if (NIL_P(rb_buf)) {
        return strio_substr(ptr, offset, len, rb_ascii8bit_encoding());
    }

    long rest = RSTRING_LEN(ptr->string) - offset;
    if (len > rest) len = rest;
    rb_str_resize(rb_buf, len);
    rb_enc_associate(rb_buf, rb_ascii8bit_encoding());
    MEMCPY(RSTRING_PTR(rb_buf), RSTRING_PTR(ptr->string) + offset, char, len);
    return rb_buf;
}

putc(obj) → obj

See IO#putc.

static VALUE
strio_putc(VALUE self, VALUE ch)
{
    struct StringIO *ptr = writable(self);
    VALUE str;

    check_modifiable(ptr);
    if (RB_TYPE_P(ch, T_STRING)) {
        if (NIL_P(ptr->string)) return ch;
        str = rb_str_substr(ch, 0, 1);
    }
    else {
        char c = NUM2CHR(ch);
        if (NIL_P(ptr->string)) return ch;
        str = rb_str_new(&c, 1);
    }
    strio_write(self, str);
    return ch;
}

read([length [, outbuf]]) → string, outbuf, or nil

See IO#read.

static VALUE
strio_read(int argc, VALUE *argv, VALUE self)
{
    struct StringIO *ptr = readable(self);
    VALUE str = Qnil;
    long len;
    int binary = 0;

    switch (argc) {
      case 2:
        str = argv[1];
        if (!NIL_P(str)) {
            StringValue(str);
            rb_str_modify(str);
        }
        /* fall through */
      case 1:
        if (!NIL_P(argv[0])) {
            len = NUM2LONG(argv[0]);
            if (len < 0) {
                rb_raise(rb_eArgError, "negative length %ld given", len);
            }
            if (len > 0 &&
                (NIL_P(ptr->string) || ptr->pos >= RSTRING_LEN(ptr->string))) {
                if (!NIL_P(str)) rb_str_resize(str, 0);
                return Qnil;
            }
            binary = 1;
            break;
        }
        /* fall through */
      case 0:
        if (NIL_P(ptr->string)) return Qnil;
        len = RSTRING_LEN(ptr->string);
        if (len <= ptr->pos) {
            rb_encoding *enc = get_enc(ptr);
            if (NIL_P(str)) {
                str = rb_str_new(0, 0);
            }
            else {
                rb_str_resize(str, 0);
            }
            rb_enc_associate(str, enc);
            return str;
        }
        else {
            len -= ptr->pos;
        }
        break;
      default:
        rb_error_arity(argc, 0, 2);
    }
    if (NIL_P(str)) {
        rb_encoding *enc = binary ? rb_ascii8bit_encoding() : get_enc(ptr);
        str = strio_substr(ptr, ptr->pos, len, enc);
    }
    else {
        long rest = RSTRING_LEN(ptr->string) - ptr->pos;
        if (len > rest) len = rest;
        rb_str_resize(str, len);
        MEMCPY(RSTRING_PTR(str), RSTRING_PTR(ptr->string) + ptr->pos, char, len);
        if (!binary) {
            rb_enc_copy(str, ptr->string);
        }
    }
    ptr->pos += RSTRING_LEN(str);
    return str;
}

readlines(sep=$/, chomp: false) → array

readlines(limit, chomp: false) → array

readlines(sep, limit, chomp: false) → array

See IO#readlines.

static VALUE
strio_readlines(int argc, VALUE *argv, VALUE self)
{
    VALUE ary, line;
    struct StringIO *ptr = readable(self);
    struct getline_arg arg;

    if (prepare_getline_args(ptr, &arg, argc, argv)->limit == 0) {
        rb_raise(rb_eArgError, "invalid limit: 0 for readlines");
    }

    ary = rb_ary_new();
    while (!NIL_P(line = strio_getline(&arg, ptr))) {
        rb_ary_push(ary, line);
    }
    return ary;
}

reopen(other, mode = 'r+') → self

Reinitializes the stream with the given other (string or StringIO) and mode; see IO.new:

StringIO.open('foo') do |strio|
  p strio.string
  strio.reopen('bar')
  p strio.string
  other_strio = StringIO.new('baz')
  strio.reopen(other_strio)
  p strio.string
  other_strio.close
end

Output:

"foo"
"bar"
"baz"

static VALUE
strio_reopen(int argc, VALUE *argv, VALUE self)
{
    rb_io_taint_check(self);
    if (argc == 1 && !RB_TYPE_P(*argv, T_STRING)) {
        return strio_copy(self, *argv);
    }
    return strio_init(argc, argv, StringIO(self), self);
}

rewind → 0

Sets the current position and line number to zero; see Position and Line Number.

static VALUE
strio_rewind(VALUE self)
{
    struct StringIO *ptr = StringIO(self);
    ptr->pos = 0;
    ptr->lineno = 0;
    return INT2FIX(0);
}

seek(offset, whence = SEEK_SET) → 0

Sets the current position to the given integer offset (in bytes), with respect to a given constant whence; see Position.

static VALUE
strio_seek(int argc, VALUE *argv, VALUE self)
{
    VALUE whence;
    struct StringIO *ptr = StringIO(self);
    long amount, offset;

    rb_scan_args(argc, argv, "11", NULL, &whence);
    amount = NUM2LONG(argv[0]);
    if (CLOSED(self)) {
        rb_raise(rb_eIOError, "closed stream");
    }
    switch (NIL_P(whence) ? 0 : NUM2LONG(whence)) {
      case 0:
        offset = 0;
        break;
      case 1:
        offset = ptr->pos;
        break;
      case 2:
        offset = RSTRING_LEN(ptr->string);
        break;
      default:
        error_inval("invalid whence");
    }
    if (amount > LONG_MAX - offset || amount + offset < 0) {
        error_inval(0);
    }
    ptr->pos = amount + offset;
    return INT2FIX(0);
}

set_encoding(ext_enc, [int_enc[, opt]]) → strio

Specify the encoding of the StringIO as ext_enc. Use the default external encoding if ext_enc is nil. 2nd argument int_enc and optional hash opt argument are ignored; they are for API compatibility to IO.

static VALUE
strio_set_encoding(int argc, VALUE *argv, VALUE self)
{
    rb_encoding* enc;
    struct StringIO *ptr = StringIO(self);
    VALUE ext_enc, int_enc, opt;

    argc = rb_scan_args(argc, argv, "11:", &ext_enc, &int_enc, &opt);

    if (NIL_P(ext_enc)) {
        enc = rb_default_external_encoding();
    }
    else {
        enc = rb_find_encoding(ext_enc);
        if (!enc) {
            rb_io_enc_t convconfig;
            int oflags, fmode;
            VALUE vmode = rb_str_append(rb_str_new_cstr("r:"), ext_enc);
            rb_io_extract_modeenc(&vmode, 0, Qnil, &oflags, &fmode, &convconfig);
            enc = convconfig.enc2;
        }
    }
    ptr->enc = enc;
    if (!NIL_P(ptr->string) && WRITABLE(self)) {
        rb_enc_associate(ptr->string, enc);
    }

    return self;
}

set_encoding_by_bom → strio or nil

Sets the encoding according to the BOM (Byte Order Mark) in the string.

Returns self if the BOM is found, otherwise +nil.

static VALUE
strio_set_encoding_by_bom(VALUE self)
{
    struct StringIO *ptr = StringIO(self);

    if (!set_encoding_by_bom(ptr)) return Qnil;
    return rb_enc_from_encoding(ptr->enc);
}

size → integer

Returns the size of the buffer string.

static VALUE
strio_size(VALUE self)
{
    VALUE string = StringIO(self)->string;
    if (NIL_P(string)) {
        return INT2FIX(0);
    }
    return ULONG2NUM(RSTRING_LEN(string));
}

Also aliased as: length

string → string

Returns underlying string:

StringIO.open('foo') do |strio|
  p strio.string
  strio.string = 'bar'
  p strio.string
end

Output:

"foo"
"bar"

Related: StringIO#string= (assigns the underlying string).

static VALUE
strio_get_string(VALUE self)
{
    return StringIO(self)->string;
}

string = other_string → other_string

Assigns the underlying string as other_string, and sets position to zero; returns other_string:

StringIO.open('foo') do |strio|
  p strio.string
  strio.string = 'bar'
  p strio.string
end

Output:

"foo"
"bar"

Related: StringIO#string (returns the underlying string).

static VALUE
strio_set_string(VALUE self, VALUE string)
{
    struct StringIO *ptr = StringIO(self);

    rb_io_taint_check(self);
    ptr->flags &= ~FMODE_READWRITE;
    StringValue(string);
    ptr->flags = readonly_string_p(string) ? FMODE_READABLE : FMODE_READWRITE;
    ptr->pos = 0;
    ptr->lineno = 0;
    RB_OBJ_WRITE(self, &ptr->string, string);
    return string;
}

sync → true

Returns true; implemented only for compatibility with other stream classes.

static VALUE
strio_get_sync(VALUE self)
{
    StringIO(self);
    return Qtrue;
}

sync= (p1)

Returns the argument unchanged. Just for compatibility to IO.

static VALUE
strio_first(VALUE self, VALUE arg)
{
    StringIO(self);
    return arg;
}

pos → stream_position

Returns the current position (in bytes); see Position.

static VALUE
strio_get_pos(VALUE self)
{
    return LONG2NUM(StringIO(self)->pos);
}

truncate(integer) → 0

Truncates the buffer string to at most integer bytes. The stream must be opened for writing.

static VALUE
strio_truncate(VALUE self, VALUE len)
{
    VALUE string = writable(self)->string;
    long l = NUM2LONG(len);
    long plen;
    if (l < 0) {
        error_inval("negative length");
    }
    if (NIL_P(string)) return 0;
    plen = RSTRING_LEN(string);
    rb_str_resize(string, l);
    if (plen < l) {
        MEMZERO(RSTRING_PTR(string) + plen, char, l - plen);
    }
    return INT2FIX(0);
}

tty? ()

Returns false. Just for compatibility to IO.

Alias for: isatty

ungetbyte(byte) → nil

Pushes back (“unshifts”) an 8-bit byte onto the stream; see Byte IO.

static VALUE
strio_ungetbyte(VALUE self, VALUE c)
{
    struct StringIO *ptr = readable(self);

    check_modifiable(ptr);
    if (NIL_P(ptr->string)) return Qnil;
    if (NIL_P(c)) return Qnil;
    if (RB_INTEGER_TYPE_P(c)) {
        /* rb_int_and() not visible from exts */
        VALUE v = rb_funcall(c, '&', 1, INT2FIX(0xff));
        const char cc = NUM2INT(v) & 0xFF;
        strio_unget_bytes(ptr, &cc, 1);
    }
    else {
        long cl;
        SafeStringValue(c);
        cl = RSTRING_LEN(c);
        if (cl > 0) {
            strio_unget_bytes(ptr, RSTRING_PTR(c), cl);
            RB_GC_GUARD(c);
        }
    }
    return Qnil;
}

ungetc(character) → nil

Pushes back (“unshifts”) a character or integer onto the stream; see Character IO.

static VALUE
strio_ungetc(VALUE self, VALUE c)
{
    struct StringIO *ptr = readable(self);
    rb_encoding *enc, *enc2;

    check_modifiable(ptr);
    if (NIL_P(ptr->string)) return Qnil;
    if (NIL_P(c)) return Qnil;
    if (RB_INTEGER_TYPE_P(c)) {
        int len, cc = NUM2INT(c);
        char buf[16];

        enc = rb_enc_get(ptr->string);
        len = rb_enc_codelen(cc, enc);
        if (len <= 0) rb_enc_uint_chr(cc, enc);
        rb_enc_mbcput(cc, buf, enc);
        return strio_unget_bytes(ptr, buf, len);
    }
    else {
        SafeStringValue(c);
        enc = rb_enc_get(ptr->string);
        enc2 = rb_enc_get(c);
        if (enc != enc2 && enc != rb_ascii8bit_encoding()) {
            c = rb_str_conv_enc(c, enc2, enc);
        }
        strio_unget_bytes(ptr, RSTRING_PTR(c), RSTRING_LEN(c));
        RB_GC_GUARD(c);
        return Qnil;
    }
}

write(string, ...) → integer

syswrite(string) → integer

Appends the given string to the underlying buffer string. The stream must be opened for writing. If the argument is not a string, it will be converted to a string using to_s. Returns the number of bytes written. See IO#write.

static VALUE
strio_write_m(int argc, VALUE *argv, VALUE self)
{
    long len = 0;
    while (argc-- > 0) {
        /* StringIO can't exceed long limit */
        len += strio_write(self, *argv++);
    }
    return LONG2NUM(len);
}