I am trying to implement an expert system in C. I have written each rule in the expert system as a function. However, I want my system to be more flexible and can process these rules from an external file specified at run time rather than hard-coded. This will provide more efficiency as the user can modify these rules any time Something like a configuration file but not sure how to do it.
A friend of mine told me to use function pointers and then use a shared object or DLL to specify the external functions. Then the config file could tell the code where the DLL is and what the corresponding function names are.
I have come up with this code to read from shared library
pro.c
include <dlfcn.h>
#include <stdlib.h>
#include <stdio.h>
typedef int (*simple_demo_function)(int);
int main(void) {
const char *error;
void *module;
simple_demo_function demo_function;
/* Load dynamically loaded library */
module = dlopen("rules.so", RTLD_LAZY);
if (!module) {
fprintf(stderr, "Couldn't open rules.so: %s\n",
dlerror());
exit(1);
}
/* Get symbol */
dlerror();
demo_function = dlsym(module, "hello");
if ((error = dlerror())) {
fprintf(stderr, "Couldn't find hello: %s\n", error);
exit(1);
}
/* Now call the function in the DL library */
(*demo_function)(10);
/* All done, close things cleanly */
dlclose(module);
return 0;
}And this is rules.c
#include <stdio.h>
int hello(int a)
{
return a*10;
}This is my script
#!/bin/sh
# Shared library demo
# Create shared library's object file, rules.o.
gcc -fPIC -Wall -g -c -o rules.o rules.c
# Create shared library.
.
gcc -g -shared -Wl,-soname,rules.so.0 \
-o rules.so.0.0 rules.o -lc
# At this point we could just copy rules.so.0.0 into
# some directory, say /usr/local/lib.
# Now we need to call ldconfig to fix up the symbolic links.
/sbin/ldconfig -n .
# Set up the linker name.
ln -sf rules.so.0 rules.so
# Compile pro program file.
gcc -Wall -g -c pro.c
# Create program pro.
gcc pro.c -o pro -L. -lrules
# Execute the program. Note that we need to tell the program
# where the shared library is, using LD_LIBRARY_PATH.
LD_LIBRARY_PATH=.
./proBut I can force it to work
