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, CR or closing " terminates string 1=CR or closing "</tt"> terminates 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 (<tt>") 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.
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.
Calling from BBC BASIC
Entry points
- 6502 Entry Address: &FFC2 (I/O processor only)
