UNPACK(3PVM) PVM Version 3.4 UNPACK(3PVM)NAME
pvm_unpack - Unpack the active message buffer into arrays of prescribed
data type.
SYNOPSIS
C
int info = pvm_unpackf( const char *fmt, ... )
int info = pvm_upkbyte( char *xp, int nitem, int stride)
int info = pvm_upkcplx( float *cp, int nitem, int stride)
int info = pvm_upkdcplx( double *zp, int nitem, int stride)
int info = pvm_upkdouble( double *dp, int nitem, int stride)
int info = pvm_upkfloat( float *fp, int nitem, int stride)
int info = pvm_upkint( int *ip, int nitem, int stride)
int info = pvm_upkuint( unsigned int *ip, int nitem, int stride )
int info = pvm_upkushort( unsigned short *ip, int nitem, int stride )
int info = pvm_upkulong( unsigned long *ip, int nitem, int stride )
int info = pvm_upklong( long *ip, int nitem, int stride)
int info = pvm_upkshort( short *jp, int nitem, int stride)
int info = pvm_upkstr( char *sp )
Fortran
call pvmfunpack( what, xp, nitem, stride, info )
PARAMETERS
fmt Printf-like format expression specifying what to pack. (See
discussion)
nitem The total number of items to be unpacked (not the number of
bytes).
stride The stride to be used when packing the items. For example, if
stride = 2 in pvm_upkcplx, then every other complex number will
be unpacked.
xp Pointer to the beginning of a block of bytes. Can be any data
type, but must match the corresponding pack data type.
cp Complex array at least nitem*stride items long.
zp Double precision complex array at least nitem*stride items
long.
dp Double precision real array at least nitem*stride items long.
fp Real array at least nitem*stride items long.
ip Integer array at least nitem*stride items long.
jp Integer*2 array at least nitem*stride items long.
sp Pointer to a null terminated character string.
what Integer specifying the type of data being unpacked.
what options
STRING 0 REAL4 4
BYTE1 1 COMPLEX8 5
INTEGER2 2 REAL8 6
INTEGER4 3 COMPLEX16 7
info Integer status code returned by the routine. Values less than
zero indicate an error.
DESCRIPTION
Each of the pvm_upk* routines unpacks an array of the given data type
from the active receive buffer. The arguments for each of the routines
are a pointer to the array to be unpacked into, nitem which is the
total number of items to unpack, and stride which is the stride to use
when unpacking.
An exception is pvm_upkstr() which by definition unpacks a NULL termi‐
nated character string and thus does not need nitem or stride argu‐
ments. The Fortran routine pvmfunpack( STRING, ... ) expects nitem to
be the number of characters in the string and stride to be 1.
If the unpacking is successful, info will be 0. If some error occurs
then info will be < 0.
A single variable (not an array) can be unpacked by setting nitem = 1
and stride = 1.
The routine pvm_unpackf() uses a printf-like format expression to spec‐
ify what and how to unpack data from the receive buffer. All variables
are passed as addresses. A BNF-like description of the format syntax
is:
format : null | init | format fmt
init : null | '%' '+'
fmt : '%' count stride modifiers fchar
fchar : 'c' | 'd' | 'f' | 'x' | 's'
count : null | [0-9]+ | '*'
stride : null | '.' ( [0-9]+ | '*' )
modifiers : null | modifiers mchar
mchar : 'h' | 'l' | 'u'
Formats:
+ means initsend - must match an int (how) in the param list.
c pack/unpack bytes
d integer
f float
x complex float
s string
Modifiers:
h short (int)
l long (int, float, complex float)
u unsigned (int)
Future extensions to the what argument in pvmfunpack will include 64
bit types when XDR encoding of these types is available. Meanwhile
users should be aware that precision can be lost when passing data from
a 64 bit machine like a Cray to a 32 bit machine like a SPARCstation.
As a mnemonic the what argument name includes the number of bytes of
precision to expect. By setting encoding to PVMRAW (see pvmfinitsend)
data can be transferred between two 64 bit machines with full precision
even if the PVM configuration is heterogeneous.
Messages should be unpacked exactly like they were packed to insure
data integrity. Packing integers and unpacking them as floats will
often fail because a type encoding will have occurred transferring the
data between heterogeneous hosts. Packing 10 integers and 100 floats
then trying to unpack only 3 integers and the 100 floats will also
fail.
EXAMPLES
C:
info = pvm_recv( tid, msgtag );
info = pvm_upkstr( string );
info = pvm_upkint( &size, 1, 1 );
info = pvm_upkint( array, size, 1 );
info = pvm_upkdouble( matrix, size*size, 1 );
int count, *iarry;
double darry[4];
pvm_unpackf("%d", &count);
pvm_unpackf("%*d %4lf", count, iarry, darry);
Fortran:
CALL PVMFRECV( TID, MSGTAG, INFO );
CALL PVMFUNPACK( INTEGER4, NSIZE, 1, 1, INFO )
CALL PVMFUNPACK( STRING, STEPNAME, 8, 1, INFO )
CALL PVMFUNPACK( REAL4, A(5,1), NSIZE, NSIZE , INFO )
ERRORS
PvmNoData
Reading beyond the end of the receive buffer. Most likely cause
is trying to unpack more items than were originally packed into
the buffer.
PvmBadMsg
The received message can not be decoded. Most likely because
the hosts are heterogeneous and the user specified an incompati‐
ble encoding. Try setting the encoding to PvmDataDefault (see
pvm_mkbuf).
PvmNoBuf
There is no active receive buffer to unpack.
SEE ALSOpvm_pack(3PVM)pvm_send(3PVM), pvm_recv(3PVM), pvm_pkmesg(3PVM)
30 August, 1993 UNPACK(3PVM)
