How to return to the CLIPS a value from UDF?

Sergey Piskunov — Mon, 20 Apr 2026 06:36:47 -0000

Thank you, Gary

How to return to the CLIPS a value from UDF?

Gary Riley — Sun, 19 Apr 2026 20:26:56 -0000

Section 8 of the Advanced Programming Guide has ten examples of adding UDFs. Here's the first one:

8.4.1 Euler’s Number
This example demonstrates returning a mathematical constant, Euler’s number, from a user
defined function.

The AddUDF function call required in UserFunctions specifies that the CLIPS function name is
e; the return value type is a float; the UDF does not expect any arguments; and the C
implementation of the UDF is the function EulersNumber.

void UserFunctions(
  Environment *env)
  {
   AddUDF(env,"e","d",0,0,NULL,EulersNumber,"EulersNumber",NULL);
  }

The implementation of the CLIPS function e in the C function EulersNumber uses the function
CreateFloat to create the return value. The C library function exp is used to calculate the value
for Euler’s number.

#include <math.h>
void EulersNumber(
  Environment *env,
  UDFContext *udfc,
  UDFValue *out)
  {
   out->floatValue = CreateFloat(env,exp(1.0));
  }

After creating a new executable including the UDF code, the function e can be invoked within
CLIPS.

CLIPS> (e)
2.71828182845905
CLIPS>

How to return to the CLIPS a value from UDF?

Sergey Piskunov — Sun, 19 Apr 2026 19:05:09 -0000

Hello.
I want to add a fact like this one - Mode 10
(assert (Mode (get_answer_from_udf_function)))

How can do that?

Problem with g++ compiler

Sergey Piskunov — Tue, 17 Mar 2026 18:43:36 -0000

Thank you, Gary

Problem with g++ compiler

Gary Riley — Tue, 17 Mar 2026 18:09:58 -0000

The linker handles references differently between files compiled as C and files compiled as C++. If you're using the make file that came with CLIPS, create the library using "make release_cpp". That will create the library using the g++ compiler.

core % make        
   .
   .
   .            
core % gcc -Wall -o main main.c -L. -lclips -lm
core % g++ -Wall -o main main.c -L. -lclips -lm
clang++: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated [-Wdeprecated]
Undefined symbols for architecture x86_64:
  "CommandLoop(environmentData*)", referenced from:
      _main in main-386a03.o
   NOTE: found '_CommandLoop' in libclips.a[15](commline.o), declaration possibly missing 'extern "C"'
   .
   .
   .            
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
core % rm *.o
core % make release_cpp
   .
   .
   .            
core % gcc -Wall -o main main.c -L. -lclips -lm
Undefined symbols for architecture x86_64:
  "_CommandLoop", referenced from:
      _main in main-ae571b.o
   .
   .
   .            
clang: error: linker command failed with exit code 1 (use -v to see invocation)
core % g++ -Wall -x c++ -o main main.c -L. -lclips -lm 
core % mv libclips.a libclips++.a
core % g++ -Wall -x c++ -o main main.c -L. -lclips++    
core %

Problem with g++ compiler

Sergey Piskunov — Mon, 16 Mar 2026 17:17:26 -0000

Hello.
I'm trying to compile my small program

#include "./CLIPS/clips.h"

int main() {
    Environment *env = CreateEnvironment();
    Load(env, "hello.clp");
    Reset(env);
    Run(env, -1);
    DestroyEnvironment(env);
    return 0;
}

$ ls
CLIPS libclips.a main.c main.cpp hello.clp

When I'm using gcc everything good
gcc -Wall -o main main.c -L. -lclips -lm

When I'm using g++ I get errors
g++ -Wall -o main main.c -L. -lclips -lm

/usr/bin/ld: /tmp/ccXICXAv.o: in function main': main.c:(.text+0xd): undefined reference toCreateEnvironment()'
/usr/bin/ld: main.c:(.text+0x27): undefined reference to Load(environmentData*, char const*)' /usr/bin/ld: main.c:(.text+0x33): undefined reference toReset(environmentData)'
/usr/bin/ld: main.c:(.text+0x46): undefined reference to Run(environmentData*, long long)' /usr/bin/ld: main.c:(.text+0x52): undefined reference toDestroyEnvironment(environmentData)'
collect2: error: ld returned 1 exit status

so I can't build my c++ program with libclips.a library and i don't know why?

Major version ?

Gary Riley — Wed, 25 Feb 2026 18:31:12 -0000

It's in the SVN repository for this project under the code tab:

https://sourceforge.net/p/clipsrules/code/HEAD/tree/branches/70x/

Major version ?

Gary Riley — Wed, 25 Feb 2026 05:27:29 -0000

If you're willing to compile the exectuables yourself and deal with some incomplete documentation, you can consider it to be a beta release. There's enough new functionality that I'm working on a companion book for it when I eventually do release it. The automatic goal generation doesn't support backtracking like Prolog (which I last used 40 years ago),, so I'm still exploring what can be done with it. It's really quite useful for systems that need to ask questions,, but I want to fully explore other uses.

I'm hoping I can get a book finished this year and do a release shortly after, but I was thinking I'd get more work done last year but I got sidetracked exploring generative AI.

Major version ?

Nick Main — Sat, 21 Feb 2026 22:19:37 -0000

The new v7 features look amazing. Especially the backward chaining.
I was about to start hacking on some native predicates for SWI Prolog to query CLIPS facts but deferring to built-in CLIPS functionality would be much better for my use cases.

How usable is the v7 branch at the moment?
Without pressure, do you have a timeline for the v7 release?

Feature request tickets

vlad — Wed, 18 Feb 2026 18:51:01 -0000

Hello,

Since the feature request section doesn't get much traffic, it may be possible to miss entries present there. So, I'm creating this ticket as an fyi of 4 existing entries there, of which the following 2 are mine:

https://sourceforge.net/p/clipsrules/feature-requests/11/
https://sourceforge.net/p/clipsrules/feature-requests/12/

Thanks

Recent posts to Discussion

How to return to the CLIPS a value from UDF?

How to return to the CLIPS a value from UDF?

How to return to the CLIPS a value from UDF?

Problem with g++ compiler

Problem with g++ compiler

Problem with g++ compiler

Major version ?

Major version ?

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Feature request tickets