Applesoft: Internals--String Utilities (1 of 2)



Applesoft strings have two parts: the descriptor and the ASCII string.  Your

string descriptor contains the length of the string along with the address of

the strings first character.  Refer to page 137 of the Applesoft Reference

Manual for additional information on the string components.  During most

Applesoft routines the descriptor is left in memory, while a two byte pointer

to the descriptor is kept in the FAC.  The pointer is the address of the

descriptor; therefore, the actual string could be anywhere in memory.  The

statement 10 A$ = "HI" leaves a descriptor pointing to the program text.



STRINI          E3D5



STRINI obtains space for creating a string whose descriptor is pointed to by

FACMO/FACLO; it also creates a descriptor for it in DSCTMP.  On entry A =

length of the string, while FACMO/FACLO point to the string descriptor.

STRINI uses GETSPA to force garbage collection when there isn't sufficient

room; GETSPA exits with an "OUT OF MEMORY ERROR" when garbage collection

free up enough room.  GETSPA moves FRESPC and FRETOP down, making room to

store the string.  STRINI returns with the descriptor of the new string in

DSCTMP and the original pointer in DSCPNT.



STRSPA          E3DD



STRSPA obtains space for the creation of a string A bytes long, then creates

a descriptor for it in DSCTMP.  STRSPA uses GETSPA to force garbage

collection when there isn't enough room.  If garbage collection is unable to

make sufficient room, GETSPA exits with an "OUT OF MEMORY" error.  GETSPA

moves FRESPC and FRETOP down enough to store the string, then returns A

unchanged with the new descriptor in DCSTMP.



GETSPT          DA7B



GETSPT moves the descriptor pointed to by FACMO/FACLO into the memory pointed

to by FORPNT.  GETSPT also moves the string's text up to FRETOP if it isn't

in the program's text.  GETSPT frees up the string if it was a temporary

string. GETSPT uses GETSPA to initiate garbage collection, or alternatively

"OUT OF MEMORY" error when the garbage collection dosen't free up sufficient

room.



MOVINS          E5D4



Moves the string whose descriptor is pointed to by STRNG1 to memory pointed

to by FRESPA.



MOVSTR          E5E2



MOVSTR moves the string pointed to by Y,X with a length of A to memory

pointed to by FRESPA.





Apple Tech Notes





Keywords:  <None>



==================================================================



This information is from the Apple Technical Information Library.



ArticleID: TECHINFO-0000077



19960724 15:55:27.00

.