IO Interface

The IO interface includes the most common I/O routines on readers and writers. In the descriptions below, "wr" refers to a writer and "rd" to a reader. In this module, the reader or writer parameter for each routine may be omitted. If the reader parameter is omitted, Stdio.stdin is used; if the writer parameter is omitted, Stdio.stdout is used.

The following routines send characters to a writer. They flush the output before returning, so they are not recommended for use with large files. For information on more efficient writer routines, see section Wr Interface. To output numbers, these routines use procedures in the Fmt interface (see section Fmt Interface).

PROCEDURE Put(txt: TEXT; wr: Wr.T := NIL);

Output "txt" to "wr" and flush "wr".

PROCEDURE PutInt(n: INTEGER; wr: Wr.T := NIL);

Output "Fmt.Int(n)" to "wr" and flush "wr".

PROCEDURE PutReal(r: REAL; wr: Wr.T := NIL);

Output "Fmt.Real(r)" to "wr" and flush "wr".

The following routines are used to get information from a reader. The exception "Error" is raised whenever a "Get" procedure encounters syntactically invalid input, including unexpected end-of-file. Routines in the Lex interface are used to read numbers (see section Lex Interface).

PROCEDURE EOF(rd: Rd.T := NIL): BOOLEAN;

Return "TRUE" iff "rd" is at end-of-file.

PROCEDURE GetLine(rd: Rd.T := NIL): TEXT RAISES {Error};

Read a line of text from "rd" and return it. A line of text is either zero or more characters terminated by a line break, or one or more characters terminated by an end-of-file. In the former case, "GetLine" consumes the line break but does not include it in the returned value.

PROCEDURE GetChar(rd: Rd.T := NIL): CHAR RAISES {Error};

Read the next character from "rd" and return it.

PROCEDURE GetInt(rd: Rd.T := NIL): INTEGER RAISES {Error};

Read a decimal numeral from "rd" using "Lex.Int" and return its value.

PROCEDURE GetReal(rd: Rd.T := NIL): REAL RAISES {Error};

Read a real number from "rd" using "Lex.Real" and return its value.

PROCEDURE OpenRead(f: TEXT): Rd.T;

Open the file name "f" for reading and return a reader on its contents. If the file doesn't exist or is not readable, return "NIL".

PROCEDURE OpenWrite(f: TEXT): Wr.T;

Open the file named "f" for writing and return a writer on its contents. If the file exists it will be erased. If the file does not exist it will be created. If the process does not have the authority to modify or create the file, return "NIL".