Ubuntu Manpage: pvm_unpack - Unpack the active message buffer into arrays of prescribed data type.

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 terminated character
string and thus does not need nitem or stride arguments. 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 specify 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)

’*' count or stride must match an int in the param list.

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