The J DLL can be called by any program that can call DLLs.
Since J.DLL is itself used by the J session, you need to make a copy of J.DLL first before calling it from J; for example, copy it to file JJ.DLL.
File system\examples\data\jdll.h. gives C prototypes for J procedures.
Script system\examples\dll\jdll.ijs. gives examples of calling the J DLL from J.
Use procedure JDo to execute a sentence. For example, the following writes text abc to file t1.txt:
load 'dll files' cmd=: '''abc'' 1!:2 <''t1.txt''' NB. example sentence 'jj.dll JDo i *c' cd <cmd NB. send to J DLL +-+--------------------+ |0|'abc' 1!:2 <'t1.txt'| +-+--------------------+ fread 't1.txt' NB. check file was written abc
Use procedure JGetM to retrieve a J variable. The cd right argument is a name, followed by 4 pointers, which will correspond to the result datatype, rank, pointer to shape, and pointer to values. For example:
'jj.dll JDo i *c' cd <'ABC=: i.5' NB. define ABC +-+---------+ |0|ABC=: i.5| +-+---------+ 'jj.dll JGetM i *c *i *i *i *i' cd 'ABC';4#<,0 +-+---+-+-+--------+--------+ |0|ABC|4|1|13496196|13496500| +-+---+-+-+--------+--------+
The 6 items in the result are: error code (0=success), name, datatype (4=integer), rank(1), pointer to shape, and pointer to values.
The pointers refer to memory addresses within the J DLL. You should reference their values before calling the J DLL again, as further calls may invalidate the memory addresses. Use function memr to read memory and and ic to convert to J integers. For example, the shape is:
_2 ic memr 13496196 0 4 5
Once the result datatype and shape are known, you can read the values, again using memr, and convert to a J variable.
File system\examples\dll\jdll.ijs defines functions that perform the necessary conversions. For example:
load 'system\examples\dll\jdll.ijs' jdo 'ABC=: i.3 4' +-+-----------+ |0|ABC=: i.3 4| +-+-----------+ jget 'ABC' 0 1 2 3 4 5 6 7 8 9 10 11 jcmd 'q: 123456' 2 2 2 2 2 2 3 643