.TH G_PRINT 2 "8 April 1991" "Demeter" "Demeter Software"
.SH NAME
g_print \- sends the generic print message to an object.
.SH SYNOPSIS

void Universal::
.I g_print
( ostream& strm = cout )

.SH DESCRIPTION

.I g_print
prints out the object to which the message is sent in textual form,
according to the printing commands in the file
.I cd-print. 
The receiving object must be a tree object. That is, it cannot
have any cycles or shared subobjects.
.I g_print
is a generic method implemented at class Universal and inherited by any
user class.

.SH RETURN VALUES
Once an object has been created or parsed in, it can be sent the g_print
message. For example:

Compound* iCompound = new Compound();
.br
iCompound = (Compound*)iCompound->g_parse("demeter-input");
iCompound->g_print();

If the
.I strm
argument is provided, then the output is sent to the ostream in the
given
.I strm.
For example:

Compound* iCompound = new Compound();
.br
iCompound = (Compound*)iCompound->g_parse("demeter-input");
.br
ofstream outFile( "demeter-output" );
.br
iCompound->g_print( outFile );
.br
outFile.close;

Notice that since ofstream is a subclass of ostream in the C++ class
library, both output to the screen and to a disk file can be handled
smoothly by
.I g_print.

.SH EXAMPLE

The file
.I cd-print,
created by Demeter from the class dictionary at generation time, contains
the grammar the generic printer uses in printing the object to which the
message is sent.
In this file the user can add or remove printing commands to modify the
layout of the output text. There are four printing commands that can be
used:

.TP 10
*l
Add new line.
.TP
*s
Add space.
.TP
+
Indent.
.I g_print
starts a new indentation level. Indentation is
by three spaces.
.TP
-
Unindent.
.I g_print
ends the current indentation level.
.LP

As an example of the effect of the printing commands, with the following
contents in
.I cd-print:

.KS
Example = <exps> Prefix_List.
.br
Prefix : Numerical |
.br
         Compound.
.br
Numerical = <val> Real.
.br
Compound = "("
.br
           Op
.br
           <args> Prefix_List
.br
           ")"
.br
           <val> Real.
.br
Op : MulSym |
.br
     AddSym |
.br
     SubSym.
.br
MulSym = "*".
.br
AddSym = "+".
.br
SubSym = "-".
.br
Prefix_List ~ Prefix { Prefix }.
.br
   *terminal_sets* Number, Ident, String, Real.
.KE

the object with input text:

(+ (* 3.0 4.0) 12.0 5.7) 17.7

is printed as

( + ( * 3.000000 4.000000 ) 12.000000 5.700000 ) 17.700000.

The following modification of
.I cd-print
adds indentation and unindentation commands around the args
part of the compound production. We also add new lines around the args
part and before each repeated Prefix of a Prefix_list. The modified
.I cd-print
is now

.KS
Example = <exps> Prefix_List.
.br
Prefix : Numerical |
.br
         Compound.
.br
Numerical = <val> Real.
.br
Compound = "("
.br
           Op *l +
.br
           <args> Prefix_List
.br
           - *l ")" "value ="
.br
           <val> Real.
.br
Op : MulSym |
.br
     AddSym |
.br
     SubSym.
.br
MulSym = "*".
.br
AddSym = "+".
.br
SubSym = "-".
.br
Prefix_List ~ Prefix { *l Prefix }.
.br
   *terminal_sets* Number, Ident, String, Real.
.KE

and the output is

.KS
( +
.br
   ( *
.br
      3.000000
.br
      4.000000
.br
   ) value = 12.000000
.br
   5.700000
.br
) value = 17.700000
.KE

Notice that we have also added the constant string "value =" before
the val part in the same production Compound. This addition of concrete
syntax does not require recompilation and produces the improved output
shown.

.SH FILES
cd-print

.SH REFERENCES 

.I User Manual for The C++ Demeter System
.br
Walter L. Hursch
.br
Northeastern University, 1993

.I The Annotated C++ Reference Manual
.br
Margaret A. Ellis and Bjarne Stroustrup
.br
Addison-Wesley, 1990

.I C++ Primer
.br
Stanley B. Lippman
.br
Addison-Wesley, 1989