GSINIT

Initialize to read a string

Specification

6502	On entry:	On exit:
Z	undefined	0=String is non-empty or quoted 1=String is empty and unquoted
Cy	0=Space or CR terminates unquoted string 1=CR terminates unquoted string	undefined
A	undefined	First character of string; =&0D if string empty and unquoted
X	undefined	preserved
Y	Offset of first character to scan	Offset of first character of string
?&F2	LSB of start of array	preserved
?&F3	MSB of start of array	preserved

Prepares GSREAD to read a string from a character array. The string may be enclosed in double quotes (") in which case spaces in the string are preserved. The string may also contain control codes and high-order characters encoded with an escape sequence.

GSINIT starts at the position given by (?&F2,?&F3)+Y and scans forward, incrementing Y until a character other than space or CR is found.

If the string begins with " then &22 is returned in A and (?&F2,?&F3)+Y points to the character after the ". In this case the carry flag input to GSINIT has no effect; GSREAD will return characters until the closing " is reached. CR encountered before the closing " causes error &FD, Bad string.

Otherwise (?&F2,?&F3)+Y points to the first non-space character, which is returned in A. Z is set if this is CR, indicating an empty, unquoted string. GSREAD will return characters until CR is reached, or also space if GSINIT was called with Cy=0.

While processing a command line, Z=0 on exit from GSINIT indicates that an argument is present. When the first call to GSREAD returns Cy=1, the flag from GSINIT distinguishes between an empty argument and no argument.

It is safe to call GSREAD at least once following GSINIT, and repeatedly on reaching CR.

Note

The character returned by GSINIT is not necessarily the character returned by the first call to GSREAD.

Entry points

• 6502 Entry Address: &FFC2 (I/O processor only)

Regregex (talk) 17:53, 11 January 2019 (CET)