binary.n

linux系统下的音频通信

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'\" Copyright (c) 1997 by Sun Microsystems, Inc.
'\"
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'\" SCCS: @(#) binary.n 1.7 97/11/11 19:08:47
'\" 
.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