Using files and keyboard input

From NEST

[ An Introduction to SLI ]

Contents 1 Overview 1.1 Example 2 Standard streams 3 Opening and closing a stream 4 Writing to streams 4.1 Example 5 Manipulators

Overview

SLI's input/output fascilities differ from those of PostScript and are close to the stream concept of C++. However, for compatibility some PostScript output commands are implemented.

Like in C++, files are represented as streams, which can be put on the stack. All i/o commands leave their stream argument on the stack, so that operations can be chained.

Example

Print Hello World to the standard output.

SLI ] cout (Hello World) <- endl
Hello World
SLI [1] ;
SLI ]

cout is the standard output of SLI. The command <- takes the role of C++'s << output operator and prints the ASCII representation of the object at stack level 0 to the stream at level 1. After this, the object is removed and the stream remains at level 0.

The command endl corresponds to the C++ manipulator of the same name. It prints an end of line character to the stream at level 0. Again, it leaves the stream argument on the stack.

Now, the abbreviated form of pop, i.e. the command ;, is used to remove the stream object from the stack.

Standard streams

The standard streams of a UNIX program are mapped to the following names. Note that these streams should not be closed by a SLI program, since the result is undefined.

Name	Description
cin	Standart input stream.
cout	Standart output stream.
cerr	Standart error output stream.

Opening and closing a stream

Streams are objects which handle the input and output of data to or from some external target. The target of a stream can be a file, a string, a devide, or another process.

Command	Description
(name) (r) file	Open file for reading.
(name) ifstream	Open file for reading.
(name) (w) file	Open file for writing.
(name) ofstream	Open file for writing.
(string) istrstream	Open string-stream for reading.
(string) ostrstream	Open string-stream for writing.
strstream	Extract a string from a string-stream.
stream close	Close the stream.

Writing to streams

Command	Description
stream obj <-	Print ASCII representation of obj to stream.
stream obj <--	Print detailed ASCII representation of obj to stream.
stream obj =	Print ASCII representation of obj to cout.
stream obj ==	Print detailed ASCII representation of obj to cout.

Example

Print Hello World to a text file.

SLI ] (test.txt) (w) file 
SLI [1] (Hello World!) <- 
SLI [1] endl 
SLI [1] ;

Manipulators

Manipulators are used to manipulate the state of a stream object. Such changes can, for instance, affect the precision with which numbers are printed.

Manipulators take one or more arguments. In general, the manipulator leaves the stream object at the top of the stack and removes all other arguments.

Manipulator	Description
ofstream flush	Write contents of buffer to file.
ofstream endl	Line terminator.
osstream ends	char[] string terminator.
ifstream ws	Eat white-spaces.
ofstream boolalpha	Prints bool as true/false.
ofstream noboolalpha	Opposite.
fstream n setw	Set width of input/output fields to n.
stream (c) setfill	Defines a fill symbol c for the field.
ostream left	Allign to left of the field.
ostream right	Allign to right of the field.
ostream internal	Sign left and number right.
ostream showpos	Print positive sign.
ostream noshowpos	Opposite.
stream uppercase
ostream nouppercase
ostream oct	Switch to octal notation.
ostream dec	Switch to decimal notation.
ostream hex	Switch to hexadecimal notation.
ostream showbase	Show base according to use of oct/dec/hex.
ostream noshowbase	Don't show base according to use of oct/dec/hex.
ostream showpoint	Decimal point is always printed.
ostream noshowpoint	Decimal point is never printed.
ostream n setprecision	Set number of decimal places to n.
ostream fixed	Use fixed point notation.
ostream scientific	Use scientific notation.