Calling C functions

Linking C and COBOL

GnuCOBOL links with C objects directly. Compile the C file with gcc, compile the COBOL with cobc -c, and link both in one step:

gcc -c helper.c -o helper.o cobc -x -free -o main main.cob helper.o

The CALL sentence

CALL names the C function, USING lists the arguments in order, and RETURNING takes the value. C pointers map to COBOL BY REFERENCE items, and plain values to BY VALUE:

CALL "c_sqrt" USING BY VALUE WS-N RETURNING WS-RESULT.

Return values

Keep the C side simple for COBOL callers: pass everything through the USING list, keep one return value, and document whether each argument is BY VALUE or BY REFERENCE in the copybook header.

Next: Subprograms: CALL and USING

Article author: Arthur Isaev