About System function

Question

Hi~
let me ask you something.
I want to get some information about users. so, I tri to
use cfuntion 'ThUsrInfo'.
I found some example like this.
data: begin of list occurs 0.
        include structure uinfo.
data: end   of list.
call 'ThUsrInfo' id 'OPCODE' field opcode_list
                 id 'TAB'    field list-*sys*.
would you explain how to use this. and
what does "list-sys" mean? when I look at the structure
list... there is no field like that~~

Answer 1

Okay...got that...but I would still recommend that you use the FM(s).
Coming to your question, I hope this answer will be satisfactory...
CALL 'ThUsrInfo' ID 'OPCODE' FIELD OPCODE
                 ID 'TAB' FIELD USR_TABL-*SYS*.
The above statement, as you know is a direct call to the SAP Kernel. There will be a Function that is written in C somewhere deep inside the kernel and the above statement is going to call that function and get you the result.
Now, if you have consider the part <b>ID 'TAB' FIELD USR_TABL-SYS</b>, USR_TABL is a tables parameter for a function module in this case. So USR_TABL itself actually stands for the header line of the table.
But the C function that you are calling is going to return you a <i>table</i> of users. So you will have to specify a table in your C-Call too.
Normally, you will refer to the table part as <b>USR_TABL[]</b>. And here, that works equally well. In fact, in your own program, you can actually replace USR_TABL-SYS with USR_TABL[].
USR_TABL-SYS is just another way of referring to the body of an internal table, exclusively for the purposes of the C-Function call. You can see some other examples like :
  CALL 'ThSysInfo' ID 'OPCODE'      FIELD OPCODE_SEND_ADM_MSG
                   ID 'LEVEL'       FIELD ILEVEL
                   ID 'SEND_MODE'   FIELD SEND_MODE
                   ID 'SERVER_NAME' FIELD SERVER_NAME
                   ID 'TYPES'       FIELD SERVER_TYPES
                   ID 'WAIT'        FIELD WAIT
                   ID 'REQ_TBL'     FIELD IN_DATA-*SYS*
                   ID 'RSP_TBL'     FIELD OUT_DATA-*SYS*.
You do not find it documented  because it is not supposed to be used by a programmer. Personally, I had done some research some time back (when I got the same doubt as you have got now) and have shared with you what I found.
Regards,
Anand Mandalika.