OS_PrettyPrint

OS SWI Calls

» OS_PrettyPrint

OS_PrettyPrint

(SWI &44)

Use

The purpose of this call is to write an indirect string, with formatting, to all of the active output streams.

Notes

Due to a serious bug in every version of PrettyPrint since RISC OS 2.00, it is important to not end the string with a tab character – tabs must be followed by at least one visible character. Starting with a tab is fine.

Compacted text uses an escape character in the print string to indicate a dictionary entry. It is followed immediately by a byte which is the dictionary entry number. If this byte is in the range 1-255, then the appropriate string in the dictionary is substituted. If it’s 0, then the special string pointed to by R2 is substituted. (This is used in particular by the *Help command.)

The format of a dictionary is a linear list of entries, which can recursively refer to other dictionary entries; each entry is a length byte (counting itself) followed by a 0 terminated string, so an empty string has a length byte of 2. A length byte of zero terminates the dictionary. A length byte of 1 is not allowed.

This call acts like OS_Write0 with several differences:

• It will break a line at a space if the next word will not fit on the line, except at hard spaces
• Compacted text is handled
• CR causes a newline to be generated
• TAB causes tabulation to the next multiple of eight columns
• ASCII 31 acts as a hard space for formatting, but is output as 32
• ESC (ASCII 27) indicates that a dictionary entry should be substituted

The RISC OS 6 version of PrettyPrint will return the address of the default dictionary in R1 if R0, R1 and R2 are zero on entry.

See also

• OS_Write0
• RISC OS Default Dictionary
• *Help