How to pass a long by value?

Question

I'm trying to understand how to (or if it is possible to) pass a long to a C function by value. Here's my simple test C function:

#include <stdio.h>
long addone (long x) {
        printf("c got %li\n", x);
        fflush(stdout);
        return 1+x;
}

And here's my cobol code:

identification division.
program-id. ccalltest.
data division.
working-storage section.
01      my-val  usage binary-long.
01      my-rc   usage binary-long.
procedure division.
move 10 to my-val.
call 'addone' using 
        by content my-val
        giving my-rc.
display my-val.
display my-rc.
stop run.

I compile with

cobc -x -free cobolcode.cob ccode.c -lc

What actually happens, though, is C receives and prints a suspiciously large number (which may actually be a pointer, I'm not sure), instead of the value that I expect, 10. Am I doing something wrong here or is this use case not supported?

Here's an example of the program output (the non-10 numbers change from run to run):

c got 140725928122192
+0000000010
+1324668753

I'm using GnuCOBOL 3.1.2.0 and GCC 14.2.1.

Answer 1

Solution: by value

As pointed out by the commenters, the solution is to use by value, not by content. This is actually explained in the GnuCOBOL programmer's guide, section 7.8.5 (the CALL statement). The programmer's guide can be found at this link: https://gnucobol.sourceforge.io/guides.html