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.so man.macros

.TH binary n 8.0 Tcl "Tcl Built-In Commands"

.BS

'\" Note:  do not modify the .SH NAME line immediately below!

.SH NAME

binary \- Insert and extract fields from binary strings

.SH SYNOPSIS

\fBbinary format \fIformatString \fR?\fIarg arg ...\fR?

.br

\fBbinary scan \fIstring formatString \fR?\fIvarName varName ...\fR?

.BE

.SH DESCRIPTION

.PP

This command provides facilities for manipulating binary data.  The

first form, \fBbinary format\fR, creates a binary string from normal

Tcl values.  For example, given the values 16 and 22, it might produce

an 8-byte binary string consisting of two 4-byte integers, one for

each of the numbers.  The second form of the command,

\fBbinary scan\fR, does the opposite: it extracts data from a binary

string and returns it as ordinary Tcl string values.

.SH "BINARY FORMAT"

.PP

The \fBbinary format\fR command generates a binary string whose layout

is specified by the \fIformatString\fR and whose contents come from

the additional arguments.  The resulting binary value is returned.

.PP

The \fIformatString\fR consists of a sequence of zero or more field

specifiers separated by zero or more spaces.  Each field specifier is

a single type character followed by an optional numeric \fIcount\fR.

Most field specifiers consume one argument to obtain the value to be

formatted.  The type character specifies how the value is to be

formatted.  The \fIcount\fR typically indicates how many items of the

specified type are taken from the value.  If present, the \fIcount\fR

is a non-negative decimal integer or \fB*\fR, which normally indicates

that all of the items in the value are to be used.  If the number of

arguments does not match the number of fields in the format string

that consume arguments, then an error is generated.

.PP

Each type-count pair moves an imaginary cursor through the binary

data, storing bytes at the current position and advancing the cursor

to just after the last byte stored.  The cursor is initially at

position 0 at the beginning of the data.  The type may be any one of

the following characters:

.IP \fBa\fR 5

Stores a character string of length \fIcount\fR in the output string.

If \fIarg\fR has fewer than \fIcount\fR bytes, then additional zero

bytes are used to pad out the field.  If \fIarg\fR is longer than the

specified length, the extra characters will be ignored.  If

\fIcount\fR is \fB*\fR, then all of the bytes in \fIarg\fR will be

formatted.  If \fIcount\fR is omitted, then one character will be

formatted.  For example,

.RS

.CS

\fBbinary format a7a*a alpha bravo charlie\fR

.CE

will return a string equivalent to \fBalpha\\000\\000bravoc\fR.

.RE

.IP \fBA\fR 5

This form is the same as \fBa\fR except that spaces are used for

padding instead of nulls.  For example,

.RS

.CS

\fBbinary format A6A*A alpha bravo charlie\fR

.CE

will return \fBalpha bravoc\fR.

.RE

.IP \fBb\fR 5

Stores a string of \fIcount\fR binary digits in low-to-high order

within each byte in the output string.  \fIArg\fR must contain a

sequence of \fB1\fR and \fB0\fR characters.  The resulting bytes are

emitted in first to last order with the bits being formatted in

low-to-high order within each byte.  If \fIarg\fR has fewer than

\fIcount\fR digits, then zeros will be used for the remaining bits.

If \fIarg\fR has more than the specified number of digits, the extra

digits will be ignored.  If \fIcount\fR is \fB*\fR, then all of the

digits in \fIarg\fR will be formatted.  If \fIcount\fR is omitted,

then one digit will be formatted.  If the number of bits formatted

does not end at a byte boundary, the remaining bits of the last byte

will be zeros.  For example,

.RS

.CS

\fBbinary format b5b* 11100 111000011010\fR

.CE

will return a string equivalent to \fB\\x07\\x87\\x05\fR.

.RE

.IP \fBB\fR 5

This form is the same as \fBb\fR except that the bits are stored in

high-to-low order within each byte.  For example,

.RS

.CS

\fBbinary format B5B* 11100 111000011010\fR

.CE

will return a string equivalent to \fB\\xe0\\xe1\\xa0\fR.

.RE

.IP \fBh\fR 5

Stores a string of \fIcount\fR hexadecimal digits in low-to-high

within each byte in the output string.  \fIArg\fR must contain a

sequence of characters in the set ``0123456789abcdefABCDEF''.  The

resulting bytes are emitted in first to last order with the hex digits

being formatted in low-to-high order within each byte.  If \fIarg\fR

has fewer than \fIcount\fR digits, then zeros will be used for the

remaining digits.  If \fIarg\fR has more than the specified number of

digits, the extra digits will be ignored.  If \fIcount\fR is

\fB*\fR, then all of the digits in \fIarg\fR will be formatted.  If

\fIcount\fR is omitted, then one digit will be formatted.  If the

number of digits formatted does not end at a byte boundary, the

remaining bits of the last byte will be zeros.  For example,

.RS

.CS

\fBbinary format h3h* AB def\fR

.CE

will return a string equivalent to \fB\\xba\\xed\\x0f\fR.

.RE

.IP \fBH\fR 5

This form is the same as \fBh\fR except that the digits are stored in

high-to-low order within each byte.  For example,

.RS

.CS

\fBbinary format H3H* ab DEF\fR

.CE

will return a string equivalent to \fB\\xab\\xde\\xf0\fR.

.RE

.IP \fBc\fR 5

Stores one or more 8-bit integer values in the output string.  If no

\fIcount\fR is specified, then \fIarg\fR must consist of an integer

value; otherwise \fIarg\fR must consist of a list containing at least

\fIcount\fR integer elements.  The low-order 8 bits of each integer

are stored as a one-byte value at the cursor position.  If \fIcount\fR

is \fB*\fR, then all of the integers in the list are formatted.  If

the number of elements in the list is fewer than \fIcount\fR, then an

error is generated.  If the number of elements in the list is greater

than \fIcount\fR, then the extra elements are ignored.  For example,

.RS

.CS

\fBbinary format c3cc* {3 -3 128 1} 257 {2 5}\fR

.CE

will return a string equivalent to

\fB\\x03\\xfd\\x80\\x01\\x02\\x05\fR, whereas

.CS

\fBbinary format c {2 5}\fR

.CE

will generate an error.

.RE

.IP \fBs\fR 5

This form is the same as \fBc\fR except that it stores one or more

16-bit integers in little-endian byte order in the output string.  The

low-order 16-bits of each integer are stored as a two-byte value at

the cursor position with the least significant byte stored first.  For

example,

.RS

.CS

\fBbinary format s3 {3 -3 258 1}\fR

.CE

will return a string equivalent to

\fB\\x03\\x00\\xfd\\xff\\x02\\x01\fR.

.RE

.IP \fBS\fR 5

This form is the same as \fBs\fR except that it stores one or more

16-bit integers in big-endian byte order in the output string.  For

example,

.RS

.CS

\fBbinary format S3 {3 -3 258 1}\fR

.CE

will return a string equivalent to

\fB\\x00\\x03\\xff\\xfd\\x01\\x02\fR.

.RE

.IP \fBi\fR 5

This form is the same as \fBc\fR except that it stores one or more

32-bit integers in little-endian byte order in the output string.  The

low-order 32-bits of each integer are stored as a four-byte value at

the cursor position with the least significant byte stored first.  For

example,

.RS

.CS

\fBbinary format i3 {3 -3 65536 1}\fR

.CE

will return a string equivalent to

\fB\\x03\\x00\\x00\\x00\\xfd\\xff\\xff\\xff\\x00\\x00\\x10\\x00\fR.

.RE

.IP \fBI\fR 5

This form is the same as \fBi\fR except that it stores one or more one

or more 32-bit integers in big-endian byte order in the output string.

For example,

.RS

.CS

\fBbinary format I3 {3 -3 65536 1}\fR

.CE

will return a string equivalent to

\fB\\x00\\x00\\x00\\x03\\xff\\xff\\xff\\xfd\\x00\\x10\\x00\\x00\fR.

.RE

.IP \fBf\fR 5

This form is the same as \fBc\fR except that it stores one or more one

or more single-precision floating in the machine's native

representation in the output string.  This representation is not

portable across architectures, so it should not be used to communicate

floating point numbers across the network.  The size of a floating

point number may vary across architectures, so the number of bytes

that are generated may vary.  If the value overflows the

machine's native representation, then the value of FLT_MAX

as defined by the system will be used instead.  Because Tcl uses

double-precision floating-point numbers internally, there may be some

loss of precision in the conversion to single-precision.  For example,

on a Windows system running on an Intel Pentium processor,

.RS

.CS

\fBbinary format f2 {1.6 3.4}\fR

.CE

will return a string equivalent to

\fB\\xcd\\xcc\\xcc\\x3f\\x9a\\x99\\x59\\x40\fR.

.RE

.IP \fBd\fR 5

This form is the same as \fBf\fR except that it stores one or more one

or more double-precision floating in the machine's native

representation in the output string.  For example, on a

Windows system running on an Intel Pentium processor,

.RS

.CS

\fBbinary format d1 {1.6}\fR

.CE

will return a string equivalent to

\fB\\x9a\\x99\\x99\\x99\\x99\\x99\\xf9\\x3f\fR.

.RE

.IP \fBx\fR 5

Stores \fIcount\fR null bytes in the output string.  If \fIcount\fR is

not specified, stores one null byte.  If \fIcount\fR is \fB*\fR,

generates an error.  This type does not consume an argument.  For

example,

.RS

.CS

\fBbinary format a3xa3x2a3 abc def ghi\fR

.CE

will return a string equivalent to \fBabc\\000def\\000\\000ghi\fR.

.RE

.IP \fBX\fR 5

Moves the cursor back \fIcount\fR bytes in the output string.  If

\fIcount\fR is \fB*\fR or is larger than the current cursor position,

then the cursor is positioned at location 0 so that the next byte

stored will be the first byte in the result string.  If \fIcount\fR is

omitted then the cursor is moved back one byte.  This type does not

consume an argument.  For example,

.RS

.CS

\fBbinary format a3X*a3X2a3 abc def ghi\fR

.CE

will return \fBdghi\fR.

.RE

.IP \fB@\fR 5

Moves the cursor to the absolute location in the output string

specified by \fIcount\fR.  Position 0 refers to the first byte in the

output string.  If \fIcount\fR refers to a position beyond the last

byte stored so far, then null bytes will be placed in the unitialized

locations and the cursor will be placed at the specified location.  If

\fIcount\fR is \fB*\fR, then the cursor is moved to the current end of

the output string.  If \fIcount\fR is omitted, then an error will be

generated.  This type does not consume an argument. For example,

.RS

.CS

\fBbinary format a5@2a1@*a3@10a1 abcde f ghi j\fR

.CE

will return \fBabfdeghi\\000\\000j\fR.

.RE

.SH "BINARY SCAN"

.PP

The \fBbinary scan\fR command parses fields from a binary string,

returning the number of conversions performed.  \fIString\fR gives the

input to be parsed and \fIformatString\fR indicates how to parse it.

Each \fIvarName\fR gives the name of a variable; when a field is

scanned from \fIstring\fR the result is assigned to the corresponding

variable.

.PP

As with \fBbinary format\fR, the \fIformatString\fR consists of a

sequence of zero or more field specifiers separated by zero or more

spaces.  Each field specifier is a single type character followed by

an optional numeric \fIcount\fR.  Most field specifiers consume one

argument to obtain the variable into which the scanned values should

be placed.  The type character specifies how the binary data is to be

interpreted.  The \fIcount\fR typically indicates how many items of

the specified type are taken from the data.  If present, the

\fIcount\fR is a non-negative decimal integer or \fB*\fR, which

normally indicates that all of the remaining items in the data are to

be used.  If there are not enough bytes left after the current cursor

position to satisfy the current field specifier, then the

corresponding variable is left untouched and \fBbinary scan\fR returns

immediately with the number of variables that were set.  If there are

not enough arguments for all of the fields in the format string that

consume arguments, then an error is generated.

.PP

Each type-count pair moves an imaginary cursor through the binary data,

reading bytes from the current position.  The cursor is initially

at position 0 at the beginning of the data.  The type may be any one of

the following characters:

.IP \fBa\fR 5

The data is a character string of length \fIcount\fR.  If \fIcount\fR

is \fB*\fR, then all of the remaining bytes in \fIstring\fR will be

scanned into the variable.  If \fIcount\fR is omitted, then one

character will be scanned.  For example,

.RS

.CS

\fBbinary scan abcde\\000fghi a6a10 var1 var2\fR

.CE

will return \fB1\fR with the string equivalent to \fBabcde\\000\fR

stored in \fBvar1\fR and \fBvar2\fR left unmodified.

.RE

.IP \fBA\fR 5

This form is the same as \fBa\fR, except trailing blanks and nulls are stripped from

the scanned value before it is stored in the variable.  For example,

.RS

.CS

\fBbinary scan "abc efghi  \\000" a* var1\fR

.CE

will return \fB1\fR with \fBabc efghi\fR stored in \fBvar1\fR.

.RE

.IP \fBb\fR 5

The data is turned into a string of \fIcount\fR binary digits in

low-to-high order represented as a sequence of ``1'' and ``0''

characters.  The data bytes are scanned in first to last order with

the bits being taken in low-to-high order within each byte.  Any extra

bits in the last byte are ignored.  If \fIcount\fR is \fB*\fR, then

all of the remaining bits in \fBstring\fR will be scanned.  If

\fIcount\fR is omitted, then one bit will be scanned.  For example,

.RS

.CS

\fBbinary scan \\x07\\x87\\x05 b5b* var1 var2\fR

.CE

will return \fB2\fR with \fB11100\fR stored in \fBvar1\fR and

\fB1110000110100000\fR stored in \fBvar2\fR.

.RE

.IP \fBB\fR 5

This form is the same as \fBB\fR, except the bits are taken in

high-to-low order within each byte.  For example,

.RS

.CS

\fBbinary scan \\x70\\x87\\x05 b5b* var1 var2\fR

.CE

will return \fB2\fR with \fB01110\fR stored in \fBvar1\fR and

\fB1000011100000101\fR stored in \fBvar2\fR.

.RE

.IP \fBh\fR 5

The data is turned into a string of \fIcount\fR hexadecimal digits in

low-to-high order represented as a sequence of characters in the set

``0123456789abcdef''.  The data bytes are scanned in first to last

order with the hex digits being taken in low-to-high order within each

byte.  Any extra bits in the last byte are ignored.  If \fIcount\fR

is \fB*\fR, then all of the remaining hex digits in \fBstring\fR will be

scanned.  If \fIcount\fR is omitted, then one hex digit will be

scanned.  For example,

.RS

.CS

\fBbinary scan \\x07\\x86\\x05 h3h* var1 var2\fR

.CE

will return \fB2\fR with \fB706\fR stored in \fBvar1\fR and

\fB50\fR stored in \fBvar2\fR.

.RE

.IP \fBH\fR 5

This form is the same as \fBh\fR, except the digits are taken in

low-to-high order within each byte.  For example,

.RS

.CS

\fBbinary scan \\x07\\x86\\x05 H3H* var1 var2\fR

.CE

will return \fB2\fR with \fB078\fR stored in \fBvar1\fR and

\fB05\fR stored in \fBvar2\fR.

.RE

.IP \fBc\fR 5

The data is turned into \fIcount\fR 8-bit signed integers and stored

in the corresponding variable as a list. If \fIcount\fR is \fB*\fR,

then all of the remaining bytes in \fBstring\fR will be scanned.  If

\fIcount\fR is omitted, then one 8-bit integer will be scanned.  For

example,

.RS

.CS

\fBbinary scan \\x07\\x86\\x05 c2c* var1 var2\fR

.CE

will return \fB2\fR with \fB7 -122\fR stored in \fBvar1\fR and \fB5\fR

stored in \fBvar2\fR.  Note that the integers returned are signed, but

they can be converted to unsigned 8-bit quantities using an expression

like:

.CS

\fBexpr ( $num + 0x100 ) % 0x100\fR

.CE

.RE

.IP \fBs\fR 5

The data is interpreted as \fIcount\fR 16-bit signed integers

represented in little-endian byte order.  The integers are stored in

the corresponding variable as a list.  If \fIcount\fR is \fB*\fR, then

all of the remaining bytes in \fBstring\fR will be scanned.  If

\fIcount\fR is omitted, then one 16-bit integer will be scanned.  For

example,

.RS

.CS

\fBbinary scan \\x05\\x00\\x07\\x00\\xf0\\xff s2s* var1 var2\fR

.CE

will return \fB2\fR with \fB5 7\fR stored in \fBvar1\fR and \fB-16\fR

stored in \fBvar2\fR.  Note that the integers returned are signed, but

they can be converted to unsigned 16-bit quantities using an expression

like:

.CS

\fBexpr ( $num + 0x10000 ) % 0x10000\fR

.CE

.RE

.IP \fBS\fR 5

This form is the same as \fBs\fR except that the data is interpreted

as \fIcount\fR 16-bit signed integers represented in big-endian byte

order.  For example,

.RS

.CS

\fBbinary scan \\x00\\x05\\x00\\x07\\xff\\xf0 S2S* var1 var2\fR

.CE

will return \fB2\fR with \fB5 7\fR stored in \fBvar1\fR and \fB-16\fR

stored in \fBvar2\fR.

.RE

.IP \fBi\fR 5

The data is interpreted as \fIcount\fR 32-bit signed integers

represented in little-endian byte order.  The integers are stored in

the corresponding variable as a list.  If \fIcount\fR is \fB*\fR, then

all of the remaining bytes in \fBstring\fR will be scanned.  If

\fIcount\fR is omitted, then one 32-bit integer will be scanned.  For

example,

.RS

.CS

\fBbinary scan \\x05\\x00\\x00\\x00\\x07\\x00\\x00\\x00\\xf0\\xff\\xff\\xff i2i* var1 var2\fR

.CE

will return \fB2\fR with \fB5 7\fR stored in \fBvar1\fR and \fB-16\fR

stored in \fBvar2\fR.  Note that the integers returned are signed and

cannot be represented by Tcl as unsigned values.

.RE

.IP \fBI\fR 5

This form is the same as \fBI\fR except that the data is interpreted

as \fIcount\fR 32-bit signed integers represented in big-endian byte

order.  For example,

.RS

.CS

\fBbinary \\x00\\x00\\x00\\x05\\x00\\x00\\x00\\x07\\xff\\xff\\xff\\xf0 I2I* var1 var2\fR

.CE

will return \fB2\fR with \fB5 7\fR stored in \fBvar1\fR and \fB-16\fR

stored in \fBvar2\fR.

.RE

.IP \fBf\fR 5

The data is interpreted as \fIcount\fR single-precision floating point

numbers in the machine's native representation.  The floating point

numbers are stored in the corresponding variable as a list.  If

\fIcount\fR is \fB*\fR, then all of the remaining bytes in

\fBstring\fR will be scanned.  If \fIcount\fR is omitted, then one

single-precision floating point number will be scanned.  The size of a

floating point number may vary across architectures, so the number of

bytes that are scanned may vary.  If the data does not represent a

valid floating point number, the resulting value is undefined and

compiler dependent.  For example, on a Windows system running on an

Intel Pentium processor,

.RS

.CS

\fBbinary scan \\x3f\\xcc\\xcc\\xcd f var1\fR

.CE

will return \fB1\fR with \fB1.6000000238418579\fR stored in

\fBvar1\fR.

.RE

.IP \fBd\fR 5

This form is the same as \fBf\fR except that the data is interpreted

as \fIcount\fR double-precision floating point numbers in the

machine's native representation. For example, on a Windows system

running on an Intel Pentium processor,

.RS

.CS

\fBbinary scan \\x9a\\x99\\x99\\x99\\x99\\x99\\xf9\\x3f d var1\fR

.CE

will return \fB1\fR with \fB1.6000000000000001\fR

stored in \fBvar1\fR.

.RE

.IP \fBx\fR 5

Moves the cursor forward \fIcount\fR bytes in \fIstring\fR.  If

\fIcount\fR is \fB*\fR or is larger than the number of bytes after the

current cursor cursor position, then the cursor is positioned after

the last byte in \fIstring\fR.  If \fIcount\fR is omitted, then the

cursor is moved forward one byte.  Note that this type does not

consume an argument.  For example,

.RS

.CS

\fBbinary scan \\x01\\x02\\x03\\x04 x2H* var1\fR

.CE

will return \fB1\fR with \fB0304\fR stored in \fBvar1\fR.

.RE

.IP \fBX\fR 5

Moves the cursor back \fIcount\fR bytes in \fIstring\fR.  If

\fIcount\fR is \fB*\fR or is larger than the current cursor position,

then the cursor is positioned at location 0 so that the next byte

scanned will be the first byte in \fIstring\fR.  If \fIcount\fR

is omitted then the cursor is moved back one byte.  Note that this

type does not consume an argument.  For example,

.RS

.CS

\fBbinary scan \\x01\\x02\\x03\\x04 c2XH* var1 var2\fR

.CE

will return \fB2\fR with \fB1 2\fR stored in \fBvar1\fR and \fB020304\fR

stored in \fBvar2\fR.

.RE

.IP \fB@\fR 5

Moves the cursor to the absolute location in the data string specified

by \fIcount\fR.  Note that position 0 refers to the first byte in

\fIstring\fR.  If \fIcount\fR refers to a position beyond the end of

\fIstring\fR, then the cursor is positioned after the last byte.  If

\fIcount\fR is omitted, then an error will be generated.  For example,

.RS

.CS

\fBbinary scan \\x01\\x02\\x03\\x04 c2@1H* var1 var2\fR

.CE

will return \fB2\fR with \fB1 2\fR stored in \fBvar1\fR and \fB020304\fR

stored in \fBvar2\fR.

.RE

.SH "PLATFORM ISSUES"

Sometimes it is desirable to format or scan integer values in the

native byte order for the machine.  Refer to the \fBbyteOrder\fR

element of the \fBtcl_platform\fR array to decide which type character

to use when formatting or scanning integers.

.SH "SEE ALSO"

format, scan, tclvars

.SH KEYWORDS

binary, format, scan