# Using files and keyboard input

## 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.