PACK(3PVM)

NAME
pvm_pack - Pack the active message buffer with arrays of prescribed data type.

SYNOPSIS
C
	int info = pvm_packf( const char *fmt, ... )
	int info = pvm_pkbyte( char *xp, int nitem, int stride )
	int info = pvm_pkcplx( float *cp, int nitem, int stride )
	int info = pvm_pkdcplx( double *zp, int nitem, int stride )
	int info = pvm_pkdouble( double *dp, int nitem, int stride )
	int info = pvm_pkfloat( float *fp, int nitem, int stride )
	int info = pvm_pkint( int *ip, int nitem, int stride )
	int info = pvm_pkuint( unsigned int *ip, int nitem, int stride )
	int info = pvm_pkushort( unsigned short *ip, int nitem, int stride )
	int info = pvm_pkulong( unsigned long *ip, int nitem, int stride )
	int info = pvm_pklong( long *ip, int nitem, int stride )
	int info = pvm_pkshort( short *jp, int nitem, int stride )
	int info = pvm_pkstr( char *sp )
Fortran
	call pvmfpack( 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 packed (not the number of bytes).

stride
    The stride to be used when packing the items. For example, if stride = 2 in pvm_pkcplx, then every other complex number will be packed.

xp  Pointer to the beginning of a block of bytes. Can be any data type, but must match the corresponding unpack 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 packed.
    	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_pk* routines packs an array of the given data type into the active send buffer. The arguments for each of the routines are a pointer to the first item to be packed, nitem which is the total number of items to pack from this array, and stride which is the stride to use when packing.

An exception is pvm_pkstr() which by definition packs a NULL terminated character string and thus does not need nitem or stride arguments. The Fortran routine pvmfpack( STRING, ... ) expects nitem to be the number of characters in the string and stride to be 1.

A null string ("") can be packed; this is just a string with no characters before the terminating '\0'. However, packing a null string pointer, (char *)0, is not allowed.

If the packing is successful, info will be 0. If some error occurs then info will be < 0.

A single variable (not an array) can be packed by setting nitem = 1 and stride = 1.

The routine pvm_packf() uses a printf-like format expression to specify what and how to pack data into the send buffer. All variables are passed as addresses if count and stride are specified otherwise, variables are assumed to be values. 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  integers
  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 pvmfpack 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_initsend( PvmDataDefault );
	info = pvm_pkstr( "initial data" );
	info = pvm_pkint( &size, 1, 1 );
	info = pvm_pkint( array, size, 1 );
	info = pvm_pkdouble( matrix, size*size, 1 );
	msgtag = 3 ;
	info = pvm_send( tid, msgtag );

    int count, *iarry;
    double darry[4];
    pvm_packf("%+ %d %*d %4lf", PvmDataRaw, count, count, iarry, darry);

Fortran:
	CALL PVMFINITSEND(PVMRAW, INFO)
	CALL PVMFPACK( INTEGER4, NSIZE, 1, 1, INFO )
	CALL PVMFPACK( STRING, 'row 5 of NXN matrix', 19, 1, INFO )
	CALL PVMFPACK( REAL8, A(5,1), NSIZE, NSIZE , INFO )
	CALL PVMFSEND( TID, MSGTAG, INFO )

WARNINGS
Strings cannot be packed when using the PvmDataInPlace encoding, due to limitations in the implementation. Attempting to pack a string using pvm_pkstr or pvm_packf will cause error code PvmNotImpl to be returned.

ERRORS

PvmNoMem
    Malloc has failed. Message buffer size has exceeded the available memory on this host.

PvmNoBuf
    There is no active send buffer to pack into. Try calling pvm_initsend before packing message.

PvmOverflow
    Attempt to pack a value too large. E.g. packing an 8-byte long with XDR encoding if the value won't fit into 4 bytes.

SEE ALSO
pvm_initsend(3PVM), pvm_unpack(3PVM), pvm_send(3PVM), pvm_recv(3PVM), pvm_pkmesg(3PVM)