Method: String#unpack

Defined in:

pack.c

#unpack(format) ⇒ Array

Decodes str (which may contain binary data) according to the format string, returning an array of each value extracted. The format string consists of a sequence of single-character directives, summarized in the table at the end of this entry. Each directive may be followed by a number, indicating the number of times to repeat with this directive. An asterisk ("*") will use up all remaining elements. The directives sSiIlL may each be followed by an underscore ("_") or exclamation mark ("!") to use the underlying platform's native size for the specified type; otherwise, it uses a platform-independent consistent size. Spaces are ignored in the format string. See also Array#pack.

"abc \0\0abc \0\0".unpack('A6Z6')   #=> ["abc", "abc "]
"abc \0\0".unpack('a3a3')           #=> ["abc", " \000\000"]
"abc \0abc \0".unpack('Z*Z*')       #=> ["abc ", "abc "]
"aa".unpack('b8B8')                 #=> ["10000110", "01100001"]
"aaa".unpack('h2H2c')               #=> ["16", "61", 97]
"\xfe\xff\xfe\xff".unpack('sS')     #=> [-2, 65534]
"now=20is".unpack('M*')             #=> ["now is"]
"whole".unpack('xax2aX2aX1aX2a')    #=> ["h", "e", "l", "l", "o"]

This table summarizes the various formats and the Ruby classes returned by each.

Integer      |         |
Directive    | Returns | Meaning
-----------------------------------------------------------------
   C         | Integer | 8-bit unsigned (unsigned char)
   S         | Integer | 16-bit unsigned, native endian (uint16_t)
   L         | Integer | 32-bit unsigned, native endian (uint32_t)
   Q         | Integer | 64-bit unsigned, native endian (uint64_t)
             |         |
   c         | Integer | 8-bit signed (signed char)
   s         | Integer | 16-bit signed, native endian (int16_t)
   l         | Integer | 32-bit signed, native endian (int32_t)
   q         | Integer | 64-bit signed, native endian (int64_t)
             |         |
   S_, S!    | Integer | unsigned short, native endian
   I, I_, I! | Integer | unsigned int, native endian
   L_, L!    | Integer | unsigned long, native endian
             |         |
   s_, s!    | Integer | signed short, native endian
   i, i_, i! | Integer | signed int, native endian
   l_, l!    | Integer | signed long, native endian
             |         |
   S> L> Q>  | Integer | same as the directives without ">" except
   s> l> q>  |         | big endian
   S!> I!>   |         | (available since Ruby 1.9.3)
   L!> Q!>   |         | "S>" is same as "n"
   s!> i!>   |         | "L>" is same as "N"
   l!> q!>   |         |
             |         |
   S< L< Q<  | Integer | same as the directives without "<" except
   s< l< q<  |         | little endian
   S!< I!<   |         | (available since Ruby 1.9.3)
   L!< Q!<   |         | "S<" is same as "v"
   s!< i!<   |         | "L<" is same as "V"
   l!< q!<   |         |
             |         |
   n         | Integer | 16-bit unsigned, network (big-endian) byte order
   N         | Integer | 32-bit unsigned, network (big-endian) byte order
   v         | Integer | 16-bit unsigned, VAX (little-endian) byte order
   V         | Integer | 32-bit unsigned, VAX (little-endian) byte order
             |         |
   U         | Integer | UTF-8 character
   w         | Integer | BER-compressed integer (see Array.pack)

Float        |         |
Directive    | Returns | Meaning
-----------------------------------------------------------------
   D, d      | Float   | double-precision, native format
   F, f      | Float   | single-precision, native format
   E         | Float   | double-precision, little-endian byte order
   e         | Float   | single-precision, little-endian byte order
   G         | Float   | double-precision, network (big-endian) byte order
   g         | Float   | single-precision, network (big-endian) byte order

String       |         |
Directive    | Returns | Meaning
-----------------------------------------------------------------
   A         | String  | arbitrary binary string (remove trailing nulls and ASCII spaces)
   a         | String  | arbitrary binary string
   Z         | String  | null-terminated string
   B         | String  | bit string (MSB first)
   b         | String  | bit string (LSB first)
   H         | String  | hex string (high nibble first)
   h         | String  | hex string (low nibble first)
   u         | String  | UU-encoded string
   M         | String  | quoted-printable, MIME encoding (see RFC2045)
   m         | String  | base64 encoded string (RFC 2045) (default)
             |         | base64 encoded string (RFC 4648) if followed by 0
   P         | String  | pointer to a structure (fixed-length string)
   p         | String  | pointer to a null-terminated string

Misc.        |         |
Directive    | Returns | Meaning
-----------------------------------------------------------------
   @         | ---     | skip to the offset given by the length argument
   X         | ---     | skip backward one byte
   x         | ---     | skip forward one byte

Returns:

• (Array)

# File 'pack.c'

static VALUE
pack_unpack(VALUE str, VALUE fmt)
{
static const char hexdigits[] = "0123456789abcdef";
char *s, *send;
char *p, *pend;
VALUE ary;
char type;
long len, tmp_len;
int star;
#ifdef NATINT_PACK
int natint;         /* native integer */
#endif
int block_p = rb_block_given_p();
int signed_p, integer_size, bigendian_p;
#define UNPACK_PUSH(item) do { VALUE item_val = (item); if (block_p) {     rb_yield(item_val); }