binary.n

linux系统下的音频通信

.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