>_<.

#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>

typedef int(*p2func)(char*);

int open_plugin(void** plugin_handle, char* plugin_name);
int close_plugin(void* plugin_handle);
p2func import_function(void* plugin_handle, const char** error);

int main(int argc, char** argv) {
	int res;
	void* plugin_handle;
	const char* error;
	char hello_message[] = "HelLO wOrLD\n";
	p2func converter;
	
	if(argc == 1) {
		printf("hello_plugin upcase.so or downcase.so\n");
		return 1;
	}

	printf("ORIGINAL MESSAGE : %s\n", hello_message);
	
	printf("LOAD PLUG-IN ... ");
	res = open_plugin(&plugin_handle, argv[1]);
	if(res) {
		fprintf(stderr, "\nplug-in load error : %s\n", dlerror());
		return 1;
	}

	converter = import_function(plugin_handle, &error);
	if(error) {
		fprintf(stderr, "\nplug-in load error : %s\n", error);
		close_plugin(plugin_handle);
		return 1;
	} else {
		printf("success!\n");
	}

	printf("\tconverting message using plug-in\n");
	converter(hello_message);
		
	printf("\nCONVERTED MESSAGE : %s\n", hello_message);

	close_plugin(plugin_handle);
	return 0;
}

int open_plugin(void** plugin_handle, char* plugin_name) {
	*plugin_handle = dlopen(plugin_name, RTLD_NOW);

	if(*plugin_handle == NULL) {
		return 1;
	}

	return 0;
}

p2func import_function(void* plugin_handle, const char** error) {
	p2func func;

	// dlsym() is return NULL if there is no symbol in DL library.
	// If symbol has a NULL as it's value. We can not determine calling dlsym()
	// is success or not. So, We are using dlerror()
	*error = dlerror();						// clear error code

	func = dlsym(plugin_handle, "conv");
	*error = dlerror();
	if(*error) {
		return NULL;
	}

	return func;
}

int close_plugin(void* plugin_handle) {
	return dlclose(plugin_handle);
}

int conv(char* str) {
	char *ptr;

	ptr = str;
	while(*ptr != '\0') {
		*ptr = toupper(*ptr);
		ptr++;	
	}

	return 0;
}