Using files and keyboard input
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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.
The command < takes the role of C++'s << output operator.
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) (w) file | Open file for writing. |
| stream close | Close the stream. |
| Command | Description |
| (name) ifstream | Open file for reading. |
| (name) ofstream | Open file for writing. |
| (string) istrstream | Open a string-stream for reading. |
| ostrstream | Open a string-stream for writing. |
| strstream | Extract a string from a string-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. |
| obj = | Print ASCII representation of obj to cout. |
| 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 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 |
| ostream 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 | |
| ostream showpoint | decimal point is allways printed |
| ostream noshowpoint | |
| ostream n setprecision | Set number of decimal places to n. |
| ostream fixed | Use fixed point notation |
| ostream scientific | Use scientific notation |
