Error: call to undeclared function 'EXTSM'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]

Question

We are migrating our application from HP-UX to LINUX and some of the c codes are using EXTSM function for sorting, but the application uses COBOL code with GNU COBOL. So, on compiling we are getting undeclared function error. How to replace this function in c code.

error: call to undeclared function 'EXTSM'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration] EXTSM(func_cod, fcd);

We checked in the link provided below, maybe we need to use SORT instead.

https://bigdanzblog.wordpress.com/2020/11/09/cobol-sort-module-in-gnucobol/

Spot where the `EXTSM` function is implemented and forward declare it. — Jabberwocky, Apr 12 '23 at 11:31
What *is* `EXTSM`? Is it a macro? Is it a function? Where is it *declared*? Like the error message says, functions in "modern" (if you count a 24 year old standard that since have been superseded *twice* as "modern") C needs to be declared before they are called. Take it as a chance to refactor the code to make it more modern and better and more robust. — Some programmer dude, Apr 12 '23 at 11:31
Do you have a manual page for it showing what it returns and what parameters it expects (from a C point of view)? — Ted Lyngmo, Apr 12 '23 at 11:39
I found this link: https://www.microfocus.com/documentation/object-cobol/ocu42/fhexsm.htm — abhyudyagarg, Apr 12 '23 at 11:40
You could compile the C code with the `-std=c89` flag, then this error won't occur. — Jabberwocky, Apr 12 '23 at 11:41
@abhyudyagarg I found that page too but it's very hard to extract the C function prototype from that page. — Ted Lyngmo, Apr 12 '23 at 11:42
where first parameter is the function code and second is file control descriptor — abhyudyagarg, Apr 12 '23 at 11:45
@abhyudyagarg And, does it return `int`? If it doesn't, then the implicit function declaration you've used in the past made your program have undefined behavior — Ted Lyngmo, Apr 12 '23 at 11:46
@Jabberwocky but will it still sort, it might fail at run time — abhyudyagarg, Apr 12 '23 at 11:46
Ok, then your old program was "lucky" I guess. :-) Try adding this to your C code: `void EXTSM(char*, char*);` before using the function. — Ted Lyngmo, Apr 12 '23 at 11:48
I didn't get this comment: "_but will it still sort, it might fail at run time_". — Jabberwocky, Apr 12 '23 at 11:49
@Jabberwocky I meant that the error will not come after -std=C89 but will it perform as expected, is there a possibility it will fail as run time. — abhyudyagarg, Apr 12 '23 at 11:50
@TedLyngmo its a COBOL function this declaration will not work. — abhyudyagarg, Apr 12 '23 at 11:51
_"... is there a possibility it will fail as run time"_ - Yes, since the implicit declaration expects the function to return `int`. — Ted Lyngmo, Apr 12 '23 at 11:51
@abhyudyagarg with `-std=C89` your code will compile and probably work as expected. — Jabberwocky, Apr 12 '23 at 11:51
_"ts a COBOL function this declaration will not work"_ - Well: _"error: call to undeclared function 'EXTSM'; ISO C99 and later do not support implicit function declarations"_ looks like a C error, not a Cobol error. — Ted Lyngmo, Apr 12 '23 at 11:52
You should add the declaration in the **C** code, not the Cobol code. — Some programmer dude, Apr 12 '23 at 12:03
Please show the actual code that you are trying to compile. Show a function where it calls `EXTSM`. Also show the `#include`s. `sub.h` seems like a requirement. — Ted Lyngmo, Apr 12 '23 at 12:06

score 0 · Answer 1 · answered Apr 12 '23 at 17:16

EXTSM is an external COBOL SORT handler, which is available in some implementations as well as in external "products".

GnuCOBOL has no published release that provides that, if you use GnuCOBOL 3.1.2+ and are fine with patching this then you could include a work-in-progress that should already work in "most cases".
The best start would then be a current GnuCOBOL 3.2 snapshot (considered stable).

Otherwise you could replace the CALL 'EXTSM' by COBOL SORT statement, as you've recognized.

Error: call to undeclared function 'EXTSM'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]

1 Answers1