Re: Calling C from RPG: what am I doing wrong?

James,

options(*string) causes RPG to make a copy of your variable and add a x'00' to the end, then pass that temporary copy. You cannot use options(*string) for an output (or in/out) parameter.

Instead, consider passing buffy as an alphanumeric field (NOT a pointer). If it needs to be null-terminated on the RPG side, then use the %str() BIF to null-terminate it before you pass it.

Also, you forgot the RETURN VALUE on your RPG prototype. Your C prototype returns an int -- but the RPG side shows no return value. Change it to have 10i 0 as a return value, otherwise those 4 bytes that are returned could possibly be overwriting memory used for something else -- and that might be hard to catch in testing, but could result in the dreaded "unexpected results" in production.

James Lampert wrote:

I have a C procedure called by an RPG program:

In the RPG program, it is prototyped thusly:

D FOO PR EXTPROC('foo')
D * VALUE OPTIONS(*STRING)
D * VALUE OPTIONS(*STRING)
D 10I 0 VALUE
D * VALUE OPTIONS(*STRING)
D * VALUE OPTIONS(*STRING)

and called thusly:

C CALLP FOO(X,Y,I,K,BUFFY)

and the C procedure is:

int foo(char *opcode, char *filename, int len, char *key, char *buffy) {
/* here we read a record from a file, putting the record into buffy */

A printf() statement in the C procedure tells me that the record definitely gets read from the file, and it's definitely the right record. Yet when control returns to the calling program, the record is gone, and what was originally in BUFFY is back.

Obviously, I'm doing *something* wrong here.